Insects are currently the most prosperous group of animals on Earth.
The body of insects is divided into three sections: head, thorax and abdomen.
On the head of insects there are compound eyes and four pairs of appendages. Some species have simple ocelli in addition to compound eyes. The first pair of appendages is represented by antennae (antennae), which are organs of smell. The remaining three pairs form the oral apparatus. The upper lip (labrum), an unpaired fold, covers the upper jaws. The second pair of oral appendages forms the upper jaws (mandibles), the third pair - the lower jaws (maxilla), the fourth pair fuses and forms the lower lip (labium). There may be a pair of palps on the lower jaw and lower lip. The oral apparatus includes the tongue (hypopharynx), a chitinous protrusion of the floor of the oral cavity (Fig. 3). Due to the way they feed, mouthparts can be of different types. There are gnawing, gnawing-licking, piercing-sucking, sucking and licking types of mouthparts. The primary type of oral apparatus should be considered gnawing (Fig. 1).
rice. 1.
1 - upper lip, 2 - upper jaws, 3 - lower jaws, 4 - lower lip,
5 - main segment of the lower lip, 6 - “stem” of the lower lip, 7 - mandibular palp,
8 - internal chewing blade of the lower jaw, 9 - external
chewing lobe of the lower jaw, 10 - chin,
11 - false chin, 12 - sublabial palp, 13 - uvula, 14 - accessory uvula.
The chest consists of three segments, which are called prothorax, mesothorax and metathorax, respectively. Each of the thorax segments bears a pair of limbs; in flying species, there are a pair of wings on the mesothorax and metathorax. The limbs are articulated. The main segment of the leg is called the coxa, followed by the trochanter, femur, tibia and tarsus (Fig. 2). Due to the way of life, the limbs are walking, running, jumping, swimming, digging and grasping.
rice. 2. Structure diagram
insect limbs:
1 - wing, 2 - coxa, 3 - trochanter,
4 - thigh, 5 - lower leg, 6 - paw.
rice. 3.
1 - compound eyes, 2 - simple ocelli, 3 - brain, 4 - salivary
gland, 5 - goiter, 6 - front wing, 7 - hind wing, 8 - ovary,
9 - heart, 10 - hindgut, 11 - caudal seta (cerci),
12 - antenna, 13 - upper lip, 14 - mandibles (upper
jaws), 15 - maxilla (lower jaws), 16 - lower lip,
17 - subpharyngeal ganglion, 18 - abdominal nerve cord,
19 - midgut, 20 - Malpighian vessels.
The number of abdominal segments varies from 11 to 4. Lower insects have paired limbs on the abdomen; in higher insects they are modified into an ovipositor or other organs.
The integument is represented by the chitinous cuticle, hypodermis and basement membrane, protects insects from mechanical damage, water loss, and is the exoskeleton. Insects have many glands of hypodermal origin: salivary, odorous, poisonous, arachnoid, waxy, etc. The color of the integument of insects is determined by pigments contained in the cuticle or hypodermis.
rice. 4. Longitudinal section through
black cockroach head:
1 - mouth opening, 2 - pharynx,
3 - esophagus, 4 - brain
(suprapharyngeal ganglion),
5 - subpharyngeal nerve ganglion,
6 - aorta, 7 - salivary duct
glands, 8 - hypopharynx, or
subpharyngeal, 9 - preoral
cavity, 10 - anterior section
preoral cavity, or
cibarium, 11 - posterior section
preoral cavity,
or salivary.
Insect muscles, according to their histological structure, are striated; they are distinguished by their ability to contract at a very high frequency (up to 1000 times per second).
The digestive system, like that of all arthropods, is divided into three sections, the anterior and posterior sections are of ectodermal origin, the middle is of endodermal origin (Fig. 5). The digestive system begins with the oral appendages and the oral cavity, into which the ducts of 1-2 pairs of salivary glands open. The first pair of salivary glands produces digestive enzymes. The second pair of salivary glands can be modified into arachnoid or silk-secreting glands (caterpillars of many types of butterflies). The ducts of each pair unite into an unpaired canal, which opens at the base of the lower lip under the hypopharynx. The anterior section includes the pharynx, esophagus and stomach. In some species of insects, the esophagus has an extension - a goiter. In species that feed on plant foods, the stomach contains chitinous folds and teeth that facilitate grinding of food. The middle section is represented by the midgut, in which food is digested and absorbed. In its initial part, the midgut may have blind outgrowths (pyloric appendages). The pyloric appendages function as digestive glands. In many insects that feed on wood, symbiotic protozoa and bacteria settle in the intestines, secreting the enzyme cellulase and thereby facilitating the digestion of fiber. The posterior section is represented by the hindgut. At the border between the middle and posterior sections, numerous blindly closed Malpighian vessels open into the intestinal lumen. The hindgut has rectal glands that suck water from the remaining food mass.
rice. 5. Structure diagram
digestive system
black cockroach:
1 - salivary glands, 2 -
esophagus, 3 - goiter, 4 -
pyloric appendages,
5 - midgut,
6 - Malpighian vessels,
7 - hindgut,
8 - rectum.
The respiratory organs of insects are the trachea, through which gases are transported. The tracheae begin with openings - spiracles (stigmas), which are located on the sides of the mesothorax and metathorax and on each abdominal segment. The maximum number of spiracles is 10 pairs. Often stigmas have special closing valves. The trachea look like thin tubes and penetrate the entire body of the insect (Fig. 6). The terminal branches of the trachea end in a stellate tracheal cell, from which even thinner tubes extend - tracheoles. Sometimes the trachea forms small expansions - air sacs. The walls of the trachea are lined with a thin cuticle, having thickenings in the form of rings and spirals.
rice. 6. Scheme
buildings
respiratory
black systems
cockroach
The circulatory system of insects is of an open type (Fig. 7). The heart is located in the pericardial sinus on the dorsal side of the ventral body. The heart has the appearance of a tube, blindly closed at the posterior end. The heart is divided into chambers, each chamber has paired openings with valves on the sides - ostia. The number of cameras is eight or less. Each chamber of the heart has muscles that provide its contraction. The wave of heart contractions from the posterior chamber to the anterior provides one-way forward movement of blood.
Hemolymph moves from the heart into a single vessel - into the cephalic aorta and then pours into the body cavity. Through numerous openings, hemolymph enters the cavity of the pericardial sinus, then through the ostia, with the expansion of the cardiac chamber, it is sucked into the heart. Hemolymph has no respiratory pigments and is a yellowish liquid containing phagocytes. Its main function is to supply the organs with nutrients and transfer metabolic products to the excretory organs. The respiratory function of the hemolymph is insignificant; only in some aquatic insect larvae (larvae of bell-bellied mosquitoes) the hemolymph has hemoglobin, is colored bright red and is responsible for the transport of gases.
The excretory organs of insects are the Malpighian vessels and the fat body. Malpighian vessels (up to 150 in number) are of ectodermal origin, flowing into the intestinal lumen at the border between the middle and hind intestines. The excretion product is uric acid crystals. In addition to the main function of storing nutrients, the fat body of insects also serves as a “storage kidney.” The fat body contains special excretory cells that are gradually saturated with sparingly soluble uric acid.
rice. 7. Structure diagram
circulatory system
black cockroach:
1 - heart, 2 - aorta.
The central nervous system of insects consists of paired suprapharyngeal ganglia (brain), subpharyngeal ganglia and segmental ganglia of the ventral nerve cord. The brain includes three sections: protocerebrum, deutocerebrum and tritocerebrum. The protocerebrum innervates the acron and the eyes located on it. Mushroom-shaped bodies develop on the protocerebrum, to which nerves from the visual organs approach. The deutocerebrum innervates the antennae, and the tritocerebrum innervates the upper lip.
The abdominal nerve chain includes 11-13 pairs of ganglia: 3 thoracic and 8-10 abdominal. In some insects, the thoracic and abdominal segmental ganglia merge to form the thoracic and abdominal ganglia.
The peripheral nervous system consists of nerves extending from the central nervous system and sensory organs. There are neurosecretory cells, the neurohormones of which regulate the activity of the endocrine organs of insects.
The more complex the behavior of insects, the more developed their brain and mushroom bodies are.
The sensory organs of insects reach a high degree of perfection. The capabilities of their sensory apparatus often exceed those of higher vertebrates and humans.
The organs of vision are represented by simple and compound eyes (Fig. 8). Compound or compound eyes are located on the sides of the head and consist of ommatidia, the number of which in different insect species varies from 8-9 (ants) to 28,000 (dragonflies). Many insect species have color vision. Each ommatidia perceives a small part of the visual field of the entire eye, the image is composed of many small particles of the image, such vision is sometimes called “mosaic”. The role of simple ocelli has not been fully studied; it has been established that they perceive polarized light.
rice. 8.
A - compound eye (ommatidia are visible on the section), B - diagram
structure of an individual ommatidium, B - diagram of the structure of a simple
eyes: 1 - lens, 2 - crystal cone, 3 - pigment
cells, 4 - visual (retinal) cells,
5 - rhabdom (optic rod), 6 - facets (external
surface of the lens), 7 - nerve fibers.
Many insects are able to make sounds and hear them. The hearing organs and organs that produce sounds can be located in any part of the body. For example, in grasshoppers, the hearing organs (tympanic organs) are located on the shins of the front legs; there are two narrow longitudinal slits leading to the eardrum, connected to receptor cells. The organs that produce sounds are located on the front wings, with the left wing corresponding to the “bow” and the right wing to the “violin”.
The olfactory organs are represented by a set of olfactory sensilla located mainly on the antennae. The antennae of males are more developed than those of females. By smell, insects search for food, places for laying eggs, and individuals of the opposite sex. Females secrete special substances - sexual attractants that attract males. Male butterflies find females at a distance of 3-9 km.
Taste sensilla are located on the jaw and labial palps of beetles, on the legs of bees, flies, and butterflies, and on the antennae of bees and ants.
Tactile receptors, thermo- and hygroreceptors are scattered over the surface of the body, but most of them are on the antennae and palps. Many insects perceive magnetic fields and their changes; where the organs that perceive these fields are located is still unknown.
Insects are dioecious animals. Many insect species exhibit sexual dimorphism. The male reproductive system includes: paired testes and vas deferens, unpaired ejaculatory duct, copulatory organ and accessory glands. The copulatory organ includes cuticular elements - the genitals. The accessory glands secrete a secretion that dilutes the sperm and forms the spermatophore membrane. The female reproductive system includes: paired ovary and oviducts, unpaired vagina, spermatic receptacle, accessory glands. Females of some species have an ovipositor. The genitalia of males and females have a complex structure and taxonomic significance.
Insects reproduce sexually; parthenogenesis (aphids) is known for a number of species.
The development of insects is divided into two periods - embryonic, including the development of the embryo in the egg, and postembryonic, which begins from the moment the larva emerges from the egg and ends with the death of the insect. Postembryonic development occurs with metamorphosis. Based on the nature of metamorphosis, these arthropods are divided into two groups: insects with incomplete transformation (hemimetabolous) and insects with complete transformation (holometabolous).
In hemimetabolous insects, the larva is similar to the adult animal. It differs from it in its underdeveloped wings - gonads, the absence of secondary sexual characteristics, and its smaller size. Such imago-like larvae are called nymphs. The larva grows, molts, and after each molt the wing rudiments enlarge. After several molts, the older nymph emerges as an adult.
In holometabolous insects, the larva is not similar to the imago not only in structure, but also ecologically; for example, the larva of the cockchafer lives in the soil, while the imago lives in trees. After several molts, the larvae turn into pupae. During the pupal stage, the larval organs are destroyed and the body of an adult insect is formed.
rice. 9.
A - open (rider), B -
covered (butterfly),
B - hidden (fly).
The larvae of holometabolous insects do not have compound eyes or wing rudiments. Their mouthparts are of the gnawing type, and their antennae and limbs are short. According to the degree of development of the limbs, four types of larvae are distinguished: protopod, oligopod, polypod, apod. Protopod larvae have only the rudiments of thoracic legs (bees). Oligopod larvae have three pairs of normal walking legs (beetles, lacewings). Polypod larvae, in addition to three pairs of thoracic legs, have several more pairs of false legs on the abdomen (butterflies, sawflies). The abdominal legs are projections of the body wall, bearing spines and hooks on the sole. Apodal larvae do not have limbs (diptera).
According to the methods of movement, the larvae of holometabolous insects are divided into campodeoid, eruciform, wireworm and vermiform.
Campodeoid larvae have a long flexible body, running legs and sensory cerci (ground beetles). Eruciform larvae are a fleshy, slightly curved body with or without limbs (chafer beetles, bronze beetles, dung beetles). Wireworms - with a rigid body, round in diameter, with supporting cerci (click beetles, darkling beetles). Vermiformes - similar in appearance to worms, legless (diptera and many others).
Pupae are of three types: free, covered, hidden (Fig. 9). In free pupae, the rudiments of wings and limbs are clearly visible, freely separated from the body, the integument is thin and soft (beetles). In covered pupae, the rudiments grow tightly to the body, the integument is highly sclerotized (butterflies). Hidden pupae are free pupae located inside a false cocoon - puparia (flies). The puparia is an unshed hardened larval skin.
The skin of insects has a complex, multi-layered structure. First of all, they are divided into outer layer - cuticle And inner layer skin cells - hypodermis. The substance that determines the basic properties of the cuticle is the nitrogenous polysaccharide chitin, which has high mechanical and chemical resistance.
Digestive system of insects
The digestive system is divided into three general sections: the foregut, midgut, and hindgut.
The foregut includes the oral cavity into which the salivary glands open, a pharynx with highly developed muscles, an elongated esophagus, a crop - a reservoir for storing food, well developed in sucking insects, and a compact muscular stomach, grinding food, better developed in gnawing insects.
The main digestion occurs in the midgut under the action of secreted enzymes. The walls of the midgut absorb nutrients. In many insects, the midgut forms blindly closed processes that increase the digestive surface. In the thicker hindgut, excess water with dissolved low-molecular substances are absorbed, and excrement is formed, which is removed through the rectum and anus.
Excretory system of insects
Main excretory organs of insects- Malpighian vessels, tubular tubules (from two to hundreds), the closed ends of which are freely located in the abdominal cavity, with the other ends they open into the intestine at the border of the middle and hind intestines. Liquid metabolic products - excess salts, nitrogenous compounds - are selectively absorbed by the thin walls of blood vessels, concentrated and excreted through the hindgut.
Respiratory system of insects
It is represented by a complex of tracheas - air-bearing tubes with elastic walls containing chitin. Air enters the trachea through the spiracles - small paired openings located on the sides of the segments, in many insects from the mesothorax to the end of the abdomen. The spiracles contain obturator devices that regulate air exchange. Further, the tracheas branch repeatedly down to the thinnest tracheoles, penetrating the entire body and delivering air directly to the organs and tissues.
Insect circulatory system
The circulatory system of insects is not closed, i.e. Blood passes part of its path not through special vessels, but into the body cavity. The central organ is the heart, or dorsal vessel, lying in the upper part of the abdominal cavity and divided into a number (6-7) of homogeneous pulsating chambers. The heart passes into the aorta, which, moving forward, opens into the head cavity. Next, the blood spreads into the body cavity due to the work of the heart and contraction of the diaphragms, entering the vessels of the limbs, antennae and wings. Blood is sucked into the chambers of the heart through holes in the side walls. The blood of insects is called hemolymph. It is usually uncolored and does not contain hemoglobin or similar oxygen scavengers supplied directly by the tracheal system. Hemolymph carries out the transport of nutrients and excreta, as well as immune functions.
Nervous system of insects
The central nervous system is represented by the suprapharyngeal ganglion, or brain, consisting of three pairs of fused nerve ganglia. A peripharyngeal nerve ring extends from it, connected below to a pair of subpharyngeal ganglia. From them in the lower part of the body cavity stretches the abdominal nerve chain. Initially paired in each segment, the nodes in some insects merge in the thoracic region. Connected to the central nervous system is the peripheral nervous system - a set of nerves extending from the nodes to the muscles, and the sympathetic system, extending from the subpharyngeal nodes to the internal organs.
Insect sense organs
Despite their small size, insects have complex, highly sensitive sensory organs. The organs of vision are represented by complex compound eyes and simple ocelli. The compound eye consists of thousands of elementary visual units - ommatidia. Insects have developed color vision, the spectrum of which is somewhat shifted to the ultraviolet region. Simple ocelli apparently serve as additional light-sensitive organs and are capable of perceiving polarized light. Insects exhibit highly developed visual orientation; some of them orient themselves by the sun, taking into account its declination.
The main organs of smell are the antennae, which carry many special sensitive receptors. The acuity and specificity of insects' sense of smell is unusually high. Males of some moths find a female, guided by the smell of sex pheromone, from a distance of 10-12 km.
Only some insects have specially developed hearing organs. Taste receptors are concentrated mainly on the oral appendages - sensitive palps, and in some insects (butterflies and bees) they are even found on the paws. Insects have a highly specific taste, which allows them to accurately identify food objects.
In the skin of insects, in addition to numerous tactile receptors, some receptors record pressure, temperature, microvibrations of the environment and other parameters.
Reproductive system of insects
The reproductive system of insects is represented by the reproductive and accessory glands, excretory ducts and external genitalia. The female reproductive system consists of paired glands - ovaries, consisting of egg tubes. Numerous eggs are formed in them. The excretory ducts are paired oviducts coming from the ovaries, uniting into an unpaired oviduct, which opens with the genital opening. Connected to the oviduct is a chamber for storing sperm - the spermatic receptacle. In the male reproductive system, paired glands are developed - testes, consisting of small lobules that produce sperm. Paired spermatic ducts depart from them, uniting into the ejaculatory canal, passing through the copulatory organ of the male. Fertilization in insects is internal.
The class Insects are the largest and most diverse class of living creatures on Earth. It is believed that at least 10–20 insects live on our planet at any one time. The number of insect species already exceeds 1 million species, and every year entomologists describe about 10 thousand new species.
External building. All insects have a body divided into three sections: head, breast And abdomen. On the chest is three pairs of walking legs, the abdomen is devoid of limbs. Most have wings and capable of active flight.
On the head of insects one pair of antennae(feathers, antennas). These are the organs of smell. There are also insects on the head a couple of difficult(faceted) eye, and in some species, in addition to them, there is also simple eyes.
Insect mouth surrounded three pairs of mouthparts(oral organs), which form the oral apparatus, or, in other words, jaws. The upper jaw is formed by one pair of limbs; in insects it is called mandibles, or mandibles. The second pair of oral limbs forms the mandibles, or first maxillae, and the third pair grows together and forms lower lip, or second maxillae. On the lower jaw and lower lip there may be
a pair of palps. In addition, the composition of the oral limbs also includes upper lip- This is a mobile outgrowth of the first segment of the head. Thus, the oral apparatus of an insect consists of an upper lip, a pair of upper jaws, a pair of lower jaws and a lower lip. This is the so-called oral apparatus gnawing type.
Depending on the method of feeding, oral apparatus can be of the following different types:
Mouth apparatus gnawing type - characteristic of insects that feed on tough plant foods (beetles, Orthoptera, cockroaches, butterfly caterpillars). This is the most ancient, original type of oral apparatus;
Mouth apparatus sucking type - mouthparts of butterflies;
Mouth apparatus licking - in flies.
Mouth apparatus piercing-sucking type - mouthparts of bedbugs, mosquitoes, scale insects, aphids;
Mouth apparatus lapping type – These are the mouthparts of bees and bumblebees.
The insect's thorax consists of three segments: anterior, average- And metathorax. On each thoracic segment there is a pair walking legs. On the mesothorax and metathorax in flying species there are most often two pairs wings.
Walking legs consist of five members which are called basin, trochanter, hip, shin And paw with claws. The leg segments are articulated using joints and form a system of levers. Due to different lifestyles, walking legs are running(cockroaches, ground beetles, bedbugs), jumping(hind leg of a grasshopper or flea), swimming(hind leg of the swimming beetle and water-loving beetle), digging(front leg of the mole cricket), grasping(front leg of the praying mantis), collective(hind leg of a bee) and others.
The abdomen of the most evolutionarily advanced ones is characterized by a decrease in the number of segments (from 11 to 4-5 in Hymenoptera and Diptera). Insects have no limbs on their abdomen, or they are modified to sting(bees, wasps), ovipositor(grasshoppers, locusts) or churches(cockroaches).
Covers of the body. The body is covered with chitinized cuticle. The cuticle is not solid, but has hard plates called sclerites, and soft articular membranes. The sclerites are connected to each other through soft articular membranes, so the cuticle of insects is mobile. Sclerites of the dorsal
Type Arthropods class Insects
sides of the body are called tergites, sclerites of the ventral side – sternites, and the sclerites of the lateral side of the body are playrites. The cuticle protects the body from external influences. There is tissue underneath the cuticle hypodermis, which produces the cuticle. The most superficial layer of the cuticle is called epicuticle and it is formed by fat-like substances, so the integument of insects is not permeable to either water or gases. This allowed insects, as well as arachnids, to colonize the driest areas of the globe. The cuticle simultaneously performs the function exoskeleton: Serves as a site for muscle attachment. Periodically insects molt, i.e. they shed the cuticle.
Musculature insects consists of striated fibers that form powerful muscle bundles, i.e. the muscles of insects are represented by separate bundles, and not a bag like those of worms. Insect muscles are distinguished by their ability to contract at a very high frequency (up to 1000 times per second!), which is why insects can run and fly so fast.
Body cavity. The body cavity of insects is mixed - mixocoel.
Digestive system typical, consists of front, average And rear intestines. The foregut is presented mouth, throat, short esophagus And stomach. The mouth is surrounded by three pairs jaws. Ducts open into the oral cavity salivary glands. The salivary glands can mutate and produce a silky thread, turning into spinning glands (in the caterpillars of many species of butterflies). In blood-sucking species, the salivary glands produce a substance that prevents blood clotting. Some types of insects have an enlarged esophagus - goiter, serving for more complete digestion of food. In species that feed on solid food, there are peculiar chitinous folds in the stomach - teeth, promoting the grinding of food. IN midgut absorption of food occurs. The midgut may have blind outgrowths, increasing the suction surface. Hindgut ends anus. At the border between the midgut and hindgut, numerous blindly closed malpighian vessels. These are the excretory organs.
Many insects have symbiotic protozoa and bacteria in their intestines that can break down fiber. The nutritional spectrum of insects is extremely diverse. Among insects there are omnivorous, herbivorous, and predatory species. There are species that feed on carrion, manure, plant debris, blood, and tissues of living organisms. Some species have adapted to assimilate such low-nutrient substances as wax, hair, feathers, and ungulate horns.
Respiratory system – tracheal system. It starts with holes - spiracles, or stigmas, which are located on the sides of the mesothorax and metathorax and on each abdominal segment. Often stigmas have special closing valves, and air selectively enters the well-developed tracheal system. Trachea These are air tubes, which are deep invaginations of the cuticle. The tracheae penetrate the entire body of the insect, branching into increasingly thinner tubes - tracheoles. The tracheae have chitinous rings and spirals that prevent the walls from collapsing. The tracheal system transports gases. Smallest
Type Arthropods class Insects
tracheoles approach every cell of the insect's body, so insects do not suffer from shortness of breath, i.e. do not suffocate even during the fastest flight. But the role of hemolymph (the so-called blood of arthropods) in the transport of gases is small.
Insects can perform respiratory movements through active expansion and contraction of the abdomen.
Many larvae living in water (larvae of dragonflies and mayflies) develop so-called tracheal gills - external protrusions of the tracheal system.
Circulatory system relatively poorly developed in insects. Heart is in pericardial sinus, on the dorsal side of the abdomen. The heart is a tube, blindly closed at the rear end, divided into chambers and having paired holes with valves on the sides - ostia. Muscles that contract the chambers are connected to each chamber of the heart. Hemolymph from the heart it moves along the aorta to the anterior part of the body and pours into the body cavity. In the body cavity, hemolymph washes all internal organs. Then, through numerous openings, the hemolymph enters the pericardial sinus, then through the ostia, with the expansion of the cardiac chamber, it is sucked into the heart. Hemolymph has no respiratory pigments and is a yellowish liquid containing phagocytes. Its main function is the transport of nutrients to all organs and metabolic products to the excretory organs. The speed of hemolymph flow is not high. For example, in the Cockroach, hemolymph circulates in the circulatory system in 25 minutes. The respiratory function of the hemolymph is insignificant, but in some aquatic insect larvae (bloodworms, bell-bellied mosquito larvae) the hemolymph contains hemoglobin, is colored bright red and is responsible for the transport of gases.
Excretory organs. In insects these include malpighian vessels And fat body. Malpighian vessels- These are blind protrusions on the border between the midgut and hindgut. Malpighian vessels (there are up to 200 or more of them) absorb metabolic products from the hemolymph. Protein metabolism products turn into crystals uric acid, and the liquid is actively reabsorbed (absorbed) by the vascular epithelium and returned to the body. Uric acid crystals enter the hindgut and are excreted with excrement.
Fat body In insects, in addition to the main function of accumulating reserve nutrients, it also serves as a “storage bud”, it has special excretory cells that are gradually saturated with poorly soluble uric acid. The fat body surrounds all internal organs. The yellowish or whitish mass that protrudes from the crushed insect is nothing more than a fat body.
Nervous system. Insects have a nervous system ladder type. The suprapharyngeal nerve nodes (and a pair of them) merged and formed the so-called “ brain" Each thoracic and abdominal segment contains a pair of ganglia ventral nerve cord.
The sensory organs of insects are diverse, complex and very well developed. Insects have compound compound eyes And simple eyes. Compound eyes are made up of separate functional units ommatidia(facets), the number of which varies among different species of insects. In active dragonflies, which
Type Arthropods class Insects
considered the most voracious predators among insects, each eye consists of 28 thousand ommatidia; and in ants, especially in individuals living underground, the number of ommatidia decreases to 8-9 thousand. Some insects have color vision, and color perception is shifted towards short-wavelength rays: they see the ultraviolet part of the spectrum and do not see red colors. Vision mosaic. There may be three or five simple ocelli. The role of simple ocelli has not been fully studied, but it has been proven that they perceive polarized light, with the help of which insects navigate in cloudy weather.
Many insects are able to make sounds and hear them. Hearing organs can be located on the shins of the front legs, at the base of the wings, on the anterior segments of the abdomen. The organs that produce sounds in insects are also diverse.
Olfactory organs located mainly on the antennae, which are most developed in males. Organs of taste are located not only in the oral cavity, but also on other organs, for example, on the legs of butterflies, bees, flies, and even on the antennae of bees and ants.
Scattered over the entire surface of the insect's body sensory cells that are associated with sensitive a hair's breadth. When humidity, pressure, wind blow, or mechanical action changes, the position of the hair changes, the receptor cell is excited and transmits a signal to the “brain”.
Many insects perceive magnetic fields and their changes, but entomologists do not yet know where the organs that perceive these fields are located.
Insects have balance organs.
Reproductive organs. Insects dioecious. Reproduction is only sexual. Many insects exhibit sexual dimorphism- males can be smaller (in many butterflies) or have a completely different color (gypsy moth butterflies), sometimes males have larger feathery antennae, in some species some individual organs are strongly developed (for example, the upper jaws of a male stag beetle look like horns). In males there are in the abdomen pair of testes, from which they depart vas deferens merging into unpaired ejaculatory duct ending copulatory organ at the posterior end of the body. Females have two ovaries, they open into steam rooms oviducts, which connect into an unpaired vagina opening at the posterior end of the abdomen genital opening.
Fertilization internal. During mating, the male's copulatory organ is inserted into the female's genital opening and the sperm enters spermatheca, from where - into the vagina, where fertilization of the eggs occurs. In some species, sperm in the spermatic receptacle remain alive for several years. The queen bee, for example, has a mating flight once in her life, but she lives and lays eggs all her life (4-5 years).
There are known cases in insects parthenogenetic, those. without fertilization, reproduction (this is a variant of sexual reproduction). Throughout the summer, female aphids give birth to larvae from unfertilized eggs, from which only females develop; only in the fall do both males and females emerge from the larvae, mating occurs, and the fertilized eggs overwinter. From parthenogenetic
Type Arthropods class Insects
eggs in social Hymenoptera (bees, wasps, ants) produce haploid (i.e., with a single set of chromosomes) males.
Development insects are divided into two periods - embryonic, including the development of the embryo in the egg, and postembryonic, which begins from the moment the young animal emerges from the egg. Postembryonic development in lower primitive insects proceeds without metamorphosis. For most, development occurs with metamorphosis(i.e. with transformation). According to the nature of metamorphosis, insects are divided into insects with incomplete transformation and insects with complete transformation.
To insects with complete transformation include insects in which the larva differs sharply from imago(adult sexually mature insects are called imago), there is a stage pupae, during which the larva’s body undergoes a restructuring and the organs of an adult insect are formed. A fully formed adult insect emerges from the pupa. Insects that have fully metamorphosed as adults do not molt. Insects with complete transformation include the following orders: Coleoptera, Hymenoptera, Diptera, Lepidoptera, Fleas and others.
In insects with incomplete transformation no pupal stage, emerges from egg larva(nymph), similar to an adult insect, but its wings and gonads are underdeveloped. The larvae eat a lot, grow intensively, molt several times, and after the last molt winged adult insects with developed gonads (sex glands) appear. Insects with incomplete transformation include, for example, the orders: Cockroaches, Mantises, Orthoptera, Lice, Homoptera and others.
The role of insects in nature huge. They are an element of biological diversity. In the structure of ecosystems, they act as consumers of the first order (these are herbivorous insects) and consumers of the second order (predatory insects), decomposers (scavengers, dung beetles). They are a food source for other insectivorous animals - birds, toads, snakes, predatory insects, lizards, spiders, etc. (In other words, insects are carriers of matter and energy through food chains). Insects are useful for humans: they pollinate his agricultural plants, they produce honey for him, they give him aesthetic pleasure, they are his pets, they are the object of scientific research. But insects attack humans and their farm animals for blood sucking, they spoil his supplies and products, they harm cultivated plants, they carry dangerous diseases, and finally, they are simply annoying and annoying.
The first scientific descriptions of the external structure of insects, presented in entomological works, date back to the 16th century. Characteristics of the histological structure by entomologists were given only three centuries later. Almost every representative of the Insect class has its own characteristic structural features, which make it possible to classify different species according to the type of limbs, antennae, wings and mouthparts.
General structure of the body of insects (with diagram and pictures)
The body of insects consists of segments - segments that vary in shape and bear various external appendages and organs. The body structure of insects includes three sections: head, thorax and abdomen. The head contains the main sensory organs and the oral apparatus. Insects have on their heads a pair of elongated segmented antennae (antennae) - organs of touch and smell - and a pair of complex compound eyes - the main visual organs. In addition, many insects have from 1 to 3 small simple ocelli - auxiliary light-sensitive organs. The oral apparatus of insects is formed on the basis of 3 pairs of jaws - modified limbs of the head segments, the third pair of jaws is fused. The chest consists of 3 large segments: prothorax, mesothorax, metathorax - and carries locomotor organs. Each segment contains one pair of jointed legs: front, middle, hind. Most insects have two pairs of wings: the anterior ones, located on the mesothorax, and the posterior ones, located on the metathorax. In a number of insects, one or both pairs of wings may be underdeveloped or even completely lost. The abdomen, consisting of numerous uniform segments, contains most of the internal organs.
Pay attention to the picture - in the structure of the abdomen of insects there are 11 segments, but most insects retain from 5 to 10 segments:
In the 8-9th segments, according to their full composition, the reproductive apparatus is located. V females of some insects (Orthoptera, Hymenoptera) have a special ovipositor organ developed on the underside of these segments. Some insects (mayflies, cockroaches, orthoptera, earwigs) have a pair of cerci on the last abdominal segment - appendages of various shapes and purposes.
Look at the detailed diagram of the structure of insects, where all the main sections are indicated:
Insect head structure
The head is the most compact part of the insect body. The segments included in the structure of the insect's head merge without discernible boundaries. Their integument forms a dense monolithic head capsule. The head has different parts, often separated by sutures. The lower front part of the head is called the clypeus, followed by the front part - the forehead, then the upper part of the head - the crown, divided by a longitudinal suture into two halves. The area behind the crown - the occiput - is located above the foramen magnum. The lateral parts of the head, located below and behind the compound eyes, are called cheeks and temples, respectively.
The main types of pairs of antennae in insects
Basic tactile and olfactory; insect organs - paired articulated antennae (or antennae) are usually movably attached on the forehead, between the eyes, in special articular pits covered with a membrane. The length and shape of antennae in insects is extremely diverse and often serves as a visual indicator for identifying families, genera, and species of insects. The number of segments in the antennae varies among different insects from three to a hundred or more. In the general structure of the antennae of insects, three sections are distinguished: the manubrium - the first segment, the stalk - the second segment and the flagellum - the totality of the remaining segments. Only the arm and leg are equipped with their own muscles and are actively mobile. Inside the leg there is a cluster of special sensitive cells - the Johnston's organ, which perceives environmental vibrations, and in some insects also sound vibrations.
Insects have numerous types of antennas. Setae-like antennae are thin, tapering towards the apex (cockroaches, grasshoppers), and filamentous antennae are thin, uniform along the entire length (ground beetles, locusts), and are also called simple due to their typical shape. The bead-shaped type of insect antennae is distinguished by convex, laterally rounded segments (darkling beetles). The segments of saw-shaped antennae have sharp corners, giving a jagged shape (click beetles and longhorned beetles). The elongated processes have segments of comb-like antennae (some species of click beetles and moths). The type of antennae of insects with the apex thickened due to the expanded last segments is called club-shaped (day butterflies). Antennae with a large, pronounced club are capitate (grave-digger beetles and bark beetles). The antennae of insects with a club consisting of wide lamellar segments are lamellar-clubs (chafer beetles and dung beetles). The spindle-shaped antennae widen towards the middle and are narrowed and pointed at the apex (hawkmoth butterflies). The cranked antennae are bent at the articulation of the handle with the rest of the body (wasps, ants). The geniculate pairs of insect antennae ending in a club or comb are called, respectively, geniculate-clubs (weevils) and geniculate-combed (stag beetles). The segments of the feathery antennae are equipped with densely located thin sensitive hairs (moths, some mosquitoes). The setaceous antennae are always short, 3-segmented, with a sensitive seta (flies) extending from the last segment. Antennae with asymmetrical segments of different shapes are called irregular (blister beetles).
Types of insect mouthparts
Insects, due to the variety of types of nutrition and methods of obtaining food, have developed a variety of mouthparts. The types of insect mouthparts serve as large systematic characters at the order level. Their study should begin with the primary and most common - the gnawing apparatus.
Insects such as dragonflies, Orthoptera, Coleoptera, Hymenoptera, most Hymenoptera and many smaller orders have gnawing mouthparts. It is intended for feeding mainly dense foods: plant, animal or organic residues. The apparatus consists of the upper lip, upper jaws, lower jaws and lower lip. The upper lip is a specialized skin fold of rectangular or oval shape. Covering other oral appendages in front, the upper lip serves as a tactile and gustatory organ. The upper jaws are monolithic, non-articulate, and heavily chitinized. The inner edge has teeth. With their help, insects capture, bite off and begin to chew food. The lower jaws retain segmentation and consist of a main segment attached to the head capsule and a stem extending from it; at the top of the stem there are external and internal chewing blades, the latter equipped with teeth. A 4-5-segmented mandibular sensory palp extends slightly to the side of the stem. The third pair of jaws in insects fuses to form the lower lip. The structure of the lip of the oral apparatus of insects is similar to the lower jaws.
The main part is divided by a transverse suture into the posterior chin and the prechin, which is bifurcated at the apex. Each half of the prechin bears a pair of small chewing lobes: internal - uvulas and external - accessory uvulas, as well as 3-4-segmented lower labial sensory palps.
The piercing-sucking mouthparts are designed to feed on a variety of liquid food hidden under the integumentary tissues of animals or plants. This apparatus is developed in bugs, homoptera (aphids, etc.), fringed pterans (thrips) and part of the order Diptera (blood-sucking mosquitoes). The outer part of the bug's mouthparts is represented by an elongated, articulated, movable proboscis, attached to the anterior edge of the head and folded under the head at rest. The proboscis is a modified lower lip. Inside the hollow proboscis lie modified upper and lower jaws - two pairs of thin, hard and pointed piercing needles or bristles. The upper jaws are simple needles that pierce the integument. A pair of lower jaws are tightly connected to each other and have two longitudinal grooves on the inner surface, forming two canals. The upper one is food - serves to absorb food. Through the lower - salivary - channel, saliva is carried into the nutrient substrate, containing enzymes necessary for the primary processing of food. The small upper lip lies at the base of the proboscis. When feeding, the insect presses its proboscis onto the substrate. The proboscis bends slightly, and a bunch of piercing needles pierces the integument and penetrates the tissue. Next, saliva is pumped and food is absorbed. Insects can damage plants with gnawing and piercing-sucking mouthparts.
The sucking mouthparts are developed in Lepidoptera (butterflies) and are adapted for obtaining nectar from the corollas of flowers. The upper and lower lips in the external structure of the sucking apparatus in representatives of the class Insects are small, in the form of simple plates; on the lower lip there are well-developed palps. The upper jaws are missing. The main part - a long, flexible proboscis that spirals at rest - is formed by modified lower jaws. Connecting with each other, the lower jaws form a tube with a large internal cavity that serves to absorb nectar. The walls of the proboscis contain many chitinous rings, which provide its elasticity and keep the food canal open.
Gnawing-licking mouthparts are found in some Hymenoptera (bees, bumblebees). It is also designed to feed on nectar, but has a completely different structure. The upper lip and upper jaws retain the typical shape of a gnawing apparatus. The main working part consists of the highly elongated, modified and interconnected mandibles and lower lip. In the lower jaws, the outer lobes are especially developed, and in the lower lip there are internal lobes, fused into a long, flexible, tubular tongue. When folded, these parts form a proboscis, which is a system of three channels of decreasing diameter inserted into each other. Through the largest external canal formed by the mandibles and elongated palps of the lower lip, abundant and nearby food or water is absorbed. The second channel - the cavity of the tongue - serves to absorb nectar from the deep corollas. The third, capillary channel, passing in the upper wall of the uvula, is the salivary channel.
A significant portion of dipterans—most flies—have a licking mouthparts. This is the most complex oral apparatus in its structure among representatives of the class Insects. It serves to feed various liquid foods and fine food suspensions (sugar juices, decomposition products of organic residues, etc.). It is a fleshy, mobile proboscis, developed mainly due to the lower lip. The proboscis ends in a pair of semicircular lobes forming an oral disc, in the center of which is a mouth opening surrounded by a row of chitinous denticles. On the surface of the blades there is a developed system of tubules that open into tiny pores. This is the filtering part of the device, absorbing only small dense particles along with liquid. The denticles of the oral disc can scrape food particles from the substrate.
Types of insect legs: structure and main types of limbs (with photos)
The insect leg consists of 5 sections. The first from the base is called the coxa - a short and wide segment, movably attached to the lower part of the segment. The second section, a small trochanteric segment, increases the mobility of the leg. The third section is the thigh, elongated and thickened, containing the most powerful motor muscles. The fourth section is the tibia, connected to the thigh by the knee joint. It is also elongated, but narrower than the hips. The last section in the structure of insect legs is the segmented leg. It usually contains from 3 to 5, less often 1-2 segments. The foot ends in a pair of chitinous claws.
As a result of adaptation to different methods of movement and performance of other functions, insects develop various types of limbs. The two most common types of insect legs—walking and running—have a common structure. The running leg is distinguished by a longer thigh and lower leg, and an elongated, narrow tarsus. The parts of the walking leg are somewhat shorter and wider; at the end of the leg there is an extension - the sole. Running legs are characteristic of fast, agile insects (ground beetles, ants). Most insects have walking legs. Other specialized and modified types of legs are represented in insects, usually in one pair, usually anterior or posterior. Jumping legs are usually hind legs. A distinctive feature of the structure of these insect limbs is a powerful, noticeably thickened thigh, containing the main muscles that act when jumping. This type is common in the orders Orthoptera (grasshoppers, crickets, locusts), Homoptera (leafhoppers and psyllids), fleas and some beetles (flea beetles). Swimming legs, also hind ones, are found in many aquatic insects - swimming and spinning beetles, rowing bugs and smoothies. This type of insect legs is characterized by a flattened, paddle-shaped shape; elastic bristles are developed along the edge of the tarsus, increasing the paddle surface. Digging legs are the forelimbs of some underground or burrowing insects (mole crickets, dung beetles). These are powerful, thick, somewhat shortened legs, the shin is shovel-shaped, widened and flattened, with large teeth. Grasping forelegs are found in some insect predators, most developed in mantises. These legs are elongated and mobile. The thigh and lower leg are covered with sharp spines. At rest, the grasping legs are folded; when prey appears, they are sharply thrown forward, pinching the victim between the thigh and lower leg. Collective legs are the hind legs of bees and bumblebees, which are used to collect pollen. The collecting device is located on the tibia and the large flattened first segment of the tarsus. It consists of a basket - a recess bordered with hairs on the lower leg - and a brush - a system of numerous small bristles on the foot. When cleaning the body, the insect successively transfers pollen to the brushes and then to the baskets of the hind legs, where pollen balls are formed - pollen.
These photos show different types of insect legs:
Main types of insect wings: photo and structure
The wing of an insect is formed by a modified fold of skin - the thinnest two-layer wing membrane, in which chitinized veins and modified tracheal vessels pass.
As you can see in the photo, there are three sides to an insect wing - the leading edge, the outer (outer) edge and the trailing (inner) edge:
Also, the structure of an insect wing includes three angles: the base, the apex and the posterior angle. According to the direction in the wing, the veins are divided into longitudinal and transverse. The basis of venation is made up of large, often branched longitudinal veins that reach the edges of the wing. Small, non-branching transverse veins are located between adjacent longitudinal ones. The veins divide the wing membrane into a number of cells, which are closed, completely limited by the veins, and open, reaching the edge of the wing.
The structure of the wings is considered in two main aspects: venation (the number and arrangement of veins) and consistency (the thickness and density of the wing plate). There are two main types of venation in insect wings. Reticulated is a dense, fine-mesh venation in which, in addition to longitudinal veins, there are many small transverse veins, forming numerous (more than 20) closed cells. Such venation is developed in dragonflies, orthoptera, lacewings and some other orders. Membranous venation - sparse, with a small number or absence of cross veins; the cells are large and few in number. This venation is developed in most orders of insects (Lepidoptera, Hymenoptera, Diptera, Coleoptera, etc.). The venation of the fore and hind wings of insects is always the same.
Based on density, there are four types of insect wings. The most common are membranous wings, formed by the thinnest, transparent wing membrane. Only butterflies have membranous wings that are opaque, since they are covered with a layer of tiny scales. The hind wings of all insects are membranous, and in many (dragonflies, lepidoptera, lacewings, hymenoptera, etc.) both pairs are membranous. In a number of insects, the fore wings are compacted and serve as a protective covering. The front wings of orthoptera, cockroaches, mantises, and earwigs are called leathery. These wings are somewhat thickened, but not hard, opaque or translucent, always colored, and usually retain venation. The front wings of bedbugs are called semi-rigid, divided transversely into a compacted base and a membranous apex with developed veins. Such wings are active in flight and serve as a protective cover. Hard wings, or elytra, are the front wings of beetles. They are strongly thickened and chitinized, often hard, colored, and venation is completely lost. These wings, while providing reliable protection for the body, do not actively work during flight. Some forms of wings are distinguished by the nature of their pubescence, for example, fringed in thrips and scaly in butterflies.
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insect body
The insect's body consists of three parts: the head, thorax and back. On the head, 6 segments have merged together and are not noticeable at all. The chest consists of 3 segments. The back part is usually made of 10, on the sides of which there are breathing holes.
Insect skeleton
Insects are invertebrate animals, therefore the structure of their body is fundamentally different from the body structure of vertebrates, which includes humans. Our body is supported by a skeleton consisting of the spine, ribs, and bones of the upper and lower limbs. Muscles are attached to this internal skeleton, with the help of which the body can move.
Insects have an external rather than an internal skeleton. The muscles are attached to it from the inside. A dense shell, the so-called cuticle, covers the entire body of the insect, including the head, legs, antennae and eyes. Movable joints connect numerous plates, segments and tubes found in the insect's body. The cuticle is similar in chemical composition to cellulose. Protein gives extra strength. Fats and wax are part of the surface of the body shell. Therefore, the insect shell is durable, despite its lightness. It is waterproof and airtight. A soft film forms on the joints. However, such a durable body shell has a significant drawback: it does not grow with the body. Therefore, insects have to periodically shed their shells. During its life, an insect changes many shells. Some of them, such as silverfish, do this more than 20 times. The insect's shell is insensitive to touch, heat and cold. But it has holes through which, using special antennae and hairs, insects determine temperature, odors and other characteristics of the environment.
The structure of insect legs
Beetles, cockroaches and ants run very fast. Bees and bumblebees use their paws to collect pollen into “baskets” located on their hind paws. Praying mantises use their front legs to hunt, pinching their prey with them. Grasshoppers and fleas, escaping from an enemy or looking for a new owner, make powerful jumps. Water beetles and bedbugs use their legs to paddle. The mole cricket digs passages in the ground with its wide front paws.
Although the legs of different insects look different, they have a similar structure. The tarsus in the coxa is attached to the thoracic segments. This is followed by the trochanter, femur and tibia. The foot is divided into several parts. At its end there is usually a claw.
Insect body parts
Hairs- microscopic sensory organs protruding from the cuticle, with the help of which insects come into contact with the outside world - they smell, taste, hear.
Ganglion- a knot-shaped accumulation of nerve cells responsible for the activity of individual parts of the body.
Larva- the early stage of insect development, following the egg stage. Variants of larvae: caterpillar, worm, nymph.
Malpighian vessels- excretory organs of an insect in the form of thin tubes that extend into the intestine between its middle section and the rectum.
Pollinator- an animal that transfers pollen from one flower to another of the same species.
Oral apparatus- organs on the head of an insect specially designed for biting, stabbing or licking, with which they take food, taste, crush and absorb it.
Segment- one of several components of the insect's body. The head consists of 6 practically fused segments, the chest - of 3, the back - usually of 10 clearly distinguishable segments
Shell change- a repeatedly repeated process in the life of an insect; it sheds its old shell in order to grow. In place of the old shell, a new one is gradually formed.
Mustache- thread-like antennae on the insect's head. They perform the functions of sensory organs and serve to obtain olfactory, gustatory, tactile and even auditory sensations.
Compound eye- a complex insect eye, consisting of individual ocelli, the number of which can reach several thousand.
Proboscis- the oral apparatus of piercing-sucking or licking-sucking insects, such as bedbugs, mosquitoes, flies, butterflies and bees.
Exuvia- the old shell of an insect, which it sheds when hatching.