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Class insects unites the most advanced arthropods. More than 1 million species are known. Unlike other arthropods, the body of insects is divided into three sections: head, breast And abdomen. Insects have compound eyes and one pair of antennae, and many have wings. Their oral organs are diverse and specialized. The more ancient type of mouthparts original to insects is gnawing. It consists of an upper lip, a pair of upper jaws, a pair of lower jaws and a lower lip.
In turn, the lower lip and lower jaws bear articulated appendages - palps, which are called chewing. The gnawing apparatus can be sucking, licking, piercing, etc. The chitinized section of the chest is divided into the prothorax, mesothorax, metathorax, articulated motionlessly and thereby providing reliable support for the moving apparatus. Each section bears a pair of walking legs, consisting of a coxa, trochanter, femur, tibia and articulated tarsus. In higher insects, the middle and back of the thorax bear a pair of wings. In insects (orthoptera, cockroaches, beetles), the front wings are modified into hard elytra, which protect the membranous hind wings from damage during flight. In dipterans (flies, mosquitoes), the hind wings have changed into club-shaped organs of balance - halteres.
The abdomen of insects consists of a varying number of segments (from 4 to 10), each of them has a pair of spiracles. Through them, air enters the insect's body. Females often have an ovipositor at the end of the abdomen. The abdominal segments are connected by strips of soft chitin, which ensures its mobility.
With this structure, the entire body of the insect, as well as its limbs, seem to be covered with notches. This is where the name comes from: insects, or "notched".
The digestive system of insects begins with the oral cavity, into which the ducts of the salivary glands open. In many insects they are specialized and play not only a digestive role. In some larvae of butterflies and hymenoptera, they secrete a protein substance from which threads are formed and the cocoon is made. The oral cavity is followed by a muscular pharynx. It serves not only as an organ for pushing food, but often also as an organ for suction. Next is the esophagus in the form of a tube. A number of insects, such as bees, have an enlarged esophagus - goiter where food accumulates. From the esophagus, food enters the muscular stomach, where it is ground by chitinous outgrowths. After this, the food is pushed into the midgut, where its final digestion and absorption occurs. At the border between the midgut and hindgut, excretory organs - thin Malpighian tubules - flow into the intestine. Undigested food remains accumulate in the hindgut and are thrown out through the anus.
Respiratory organs typical of insects - trachea. These are thin tubes, inside of which there is a spiral chitinous thread. It does not allow the walls of the tubes to collapse, which ensures the unhindered penetration of air into the insect’s body. The trachea gradually branches, penetrates all organs and tissues, and brings air to them without the participation of the circulatory system. The latter is responsible only for transporting digested food substances to the cells and tissues. In this regard, the circulatory system of insects does not receive much development. It is not closed and consists of one long dorsal vessel - hearts. Blood enters it from the body cavity and pours out between the organs.
From the blood, harmful substances (decomposition products) penetrate the Malpighian tubules, through them they enter the hind intestine and are excreted.
A characteristic feature of insects that ensures their prosperity on Earth in our time is the good development of the nervous system and sensory organs. The nervous system of insects consists of a large suprapharyngeal paired nerve ganglion, which plays the role of brain; peripharyngeal ring and ventral nerve cord. The nerves to the limbs and wings arise from the nodes of the thoracic chain. Insects have varied sense organs. The skin has formations in the form of hairs, inside of which there are receptors; very sensitive to mechanical stimuli - the organs of touch, air movement - the organs of hearing. Smell receptors are located on the antennae, taste receptors are located on the mouthparts. The organs of vision - the eyes - are built like those of crustaceans. Many insects can distinguish colors. For example, a honey bee can distinguish all the same colors as a human. Unlike humans, it also detects ultraviolet rays.
Insects are dioecious animals. Males and females often differ noticeably in external characteristics: size, color, etc. In the ancient silkworm butterfly, males are winged, and females are wingless. In the winter moth, females have greatly shortened wings.
The ovaries of females, as a rule, consist of thin oviducts, from which mature eggs enter the oviduct. The females of many insects have a special organ called spermatheca. It preserves for a long time the fertilizing fluid received by the female at the time of mating. Thus, the queen bee mates once in her life and then stores viable sperm in the seminal receptacle for three years.
When the egg passes through the oviduct, it is fertilized by this sperm. The females of some insects, such as locusts, have accessory glands that secrete mucus that coats the laid eggs. The mucus hardens, and the clutch of eggs in the ground receives reliable protection. Such a clutch of locusts, protected by hardened mucus, is called an egg capsule.
Insect development occurs with complete or incomplete transformation. In some insects, fertilized eggs produce larvae that differ sharply in structure and lifestyle from adult insects. After a series of molts and changes, they turn into a stationary pupa, from which an adult insect emerges after some time. This development was called development with complete transformation. It is characteristic of beetles, butterflies, flies, silkworms, etc.
Other insects (locusts, grasshoppers, bedbugs) develop with incomplete transformation. Their larvae are basically similar to adult insects, differing only in size and underdevelopment of the gonads.
Adult insects are the most mobile and active invertebrates. Everyone has legs, everyone is able to move, both at low and at great speed. Some units are able to jump using their hind legs, while others can swim on and under water. Insect movement is one of the most fascinating and understudied topics for zoological scientists.
Body structure
A significant portion of adult insects have three pairs of limbs. They are fixed in the lower part of the thoracic segments, a pair per segment. Usually, the legs consist of 5 parts, such as:
- Cox (basin).
- Hip.
- Shin.
- Trochanter.
- Paw.
Representatives of predatory species use such limbs for active hunting, and some individuals prefer to attack the prey by creeping up to it at a close distance. As soon as the distance is too small, the tenacious front legs are thrown out with lightning speed and bite into the victim.
And although such differences do not play a big role, when solving specialized problems they are very important. For example, grasshoppers, which have larger hind legs, have the maximum number of muscles located in the thigh. Noticing danger, they can make jumps several times the height of their body length. At the same time, the mole cricket, which is a close relative of grasshoppers, has slightly elongated forelimbs, which are intended for digging the ground.
Insects that live in water are characterized by a slow speed of movement, although some species are capable of moving very quickly, because they have paddle-shaped appendages made of hairy fringe. In aquatic beetles these appendages are located on the hind legs, while in the combing bug they are on the front legs.
The dragonfly larva is generally distinguished by a modified form of locomotion. When faced with danger, a kind of “jet engine” turns on, which throws water out of its abdomen.
Specific modifications
There are species of insects that are not able to use their limbs for their intended purpose. This is due to various modifications that they underwent during their own improvement.
So, in praying mantises, which lead a predatory lifestyle, legs are designed to firmly capture prey. They have special spikes that guarantee a death grip on the victim.
Similar modifications are present in the ranatra water bug. Representatives of the bee family are equipped with special elements for moving pollen from plants to the hive. Various modifications of the legs are not always explained by the specific nutrition. Thus, male swimming beetles have suction cups on their legs to fix the slippery female during mating.
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Bumblebees are social insects. Almost like all bees, they live in families, which consist of: large fertile queens, smaller worker bumblebees, and males. In the absence of a queen, working females can also lay eggs. Typically, a bumblebee family lives only 1 year: from spring to autumn. It is much smaller than a bee, but still has...
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Slide 7 from the presentation "Who are insects". The size of the archive with the presentation is 2568 KB.The world around us 1st grade
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Wing-body articulation
Attachment of wings to the body and their movement
The ability to fly was developed in insects throughout evolution: as is known, the most primitive orders can move only with the help of, since they do not have. Moving through the air is more advantageous in terms of speed, and, moreover, it uses much less energy than walking.
The insect wing can be compared to a double-armed lever. The short arm is represented by its inner part (base), which is hidden under the membrane, and the long arm is located on the outside: in fact, this visible part is considered to be the wing. On the inner surface of the exoskeleton, just below the junction of the wing and the body, there is a dense projection called the pleural column; this structure plays the role of a fulcrum during the swing. (photo)
When an insect is about to straighten, it contracts special muscles () attached to the back. The back will move slightly downward, pressing on the inside of the wing plate. It, in turn, rests on the playral column. In this case, the base of the wing lowers, and its outer part simultaneously goes up. If it is necessary to lower the wing, the backrest rises again, and everything returns to its original position.
Wing interaction during flight
Insects move either with the help of four (beetles, butterflies) or with the help of two. Typically, a pair of wing plates located on one side of the body, when expanded, form a single flight surface. The only exceptions are some representatives of the class. For example, among dragonflies there are both homoptera, in which they move in the same way, and heteroptera, in which each wing moves in its own way. (video)
Flight types
The division of flight into varieties can be carried out from different points of view. For example, depending on its purpose, experts distinguish two main types:
- trivial (ordinary)- flight for the purpose of obtaining food, finding a partner for, etc.
- migration- a flight carried out to search for new habitats.
This gradation is not one of the most successful, since it does not reflect the peculiarities of the functioning of the insect’s wing apparatus in a particular case. Thus, both locusts and butterflies can migrate long distances, but the specific ways in which they do this differ, and this must be taken into account. For this reason, the most convenient seems to be the functional classification of flight into passive and active methods.
Passive flight
- carried out without active muscle work, under the influence of gravity, air currents or kinetic energy accumulated in active flight (force of inertia).It happens:
Active flight
: it is possible thanks to active movements. The insect performs wing strokes, which ensure its movement forward and upward. Active movement is divided into two main types:- flapping flight- carried out using high-amplitude strokes, during which the insect moves relative to the ground.
- standing (quivering) flight- the insect makes small movements, while it hangs in the air, but does not fly forward.
All winged orders have the ability for flapping flight, while standing flight can only be demonstrated by flies, butterflies and some other, rather few, insects. At the same time, while standing still, the tip of the wing describes a figure of eight. If the insect moves forward, this figure “stretches” and the wing “draws” a sinusoid. (video)
Speed and range
It would seem that the lighter the insect, the faster it should fly, but in living nature everything often happens the other way around. The smaller the flyer, the more difficult it is for him to resist the flow of air, and the more effort he must put into moving. Therefore, medium and large flies, butterflies and dragonflies fly the fastest. Beetles are inferior to them in this: with increasing body size, Coleoptera become heavier and clumsier. For example, a hawkmoth butterfly in complete calm can move 15 m in one second (54 km/h) 1046 times per second.
External conditions such as wind and rain greatly affect the ability to fly. Typically, insects try not to take off under unfavorable environmental conditions. However, some have very unusual relationships with natural phenomena. For example, at wind speeds of up to 0.7 m/s, blue blowflies fly very actively - such an intensity of air currents has a stimulating effect on them. However, as soon as the indicator reaches large values, flight immediately becomes an extremely unpopular activity for these Diptera.
During settlement or migration, insects can sometimes make quite long flights, but not all are capable of this. For example, most flies travel a few meters in calm conditions and then sit down to rest. If you deprive them of this opportunity, they will fly a little more than a kilometer, and then get tired and fall. Others are strong enough to fly over much greater distances. For example, dragonflies have been seen in the middle of the Caribbean Sea, more than 500 km from the nearest landmass. Considering that such an insect has a sufficient reserve of strength to return back, it shows fantastic endurance results.
