Arthropods - insects
insects are arthropods;
they can be identified based on three pairs of segmented legs;
insects pollinate flowers, allowing the formation of seeds.
identify an unknown organism as a representative of insects;
describe their adaptation to the environment and lifestyle (based on body observation);
describe the way of breathing, feeding and breeding of insects;
compare complex development with complete and incomplete metamorphosis;
assess the importance of insects in nature.
Insects
Insects account for 90% of species of all animals. They are also the most diverse group. Like other arthropods, they have their bodies covered with a chitinous cuticle and segmented legs, as well as segmentation marks in the structures of the thorax and the abdomen. The vast majority of these animals live on land and have wings thanks to which they can fly. Some insects, such as ants, cockroaches, fleas, do not have wings but move quickly, running or jumping. Few insects, such as some water beetles and bugs, live in water.
Insects’ bodies are divided into heads, thorax and abdomen. On the head there is a mouth organ and sensory organs: 1 pair of antennaeantennae and eyes. Antennae are segmented, thread‑like or finger‑like processes that are used to receive tactile, olfactory and sound stimuli. On the body of insects there are 3 pairs of crotch legs and usually 2 pairs of wings.
Describing the structure of an Indian stick insect and its adaptation to the living environment.
Observation‑what‑it will be needed
adult stick insect,
magnifying glass.
Observe the external structure of the stick insect through the magnifying glass and then present it in a schematic drawing. Reproduce exactly the shape of the body and its proportions.
Determine the part of the body the arthropod legs grow from, the number of segments that make up the arthropod legs, the number of segments that makes up the abdomen, the location of spiracles.
Observe the behaviour of the stick insect in a terrarium. Determine its adaptation to life on land.
Sign individual parts of the body in the drawing.
The structure of the stick insect is in line with the insect structure plan. Adaptations to the land environment concern, among others, colour and shape of the body, the structure of feet (claws) and the covering of the body protecting against drying.
Mouths of insects
The structure of insect mouthsmouths depends on the type of food they eat, and the method of its collection and grinding. In the biting mouth there are strongly developed serrated mandibles and jaws. This type of mouth is found both in herbivorous insects such as grasshoppers, locusts and herbivorous beetles, as well as in predatory insects such as dragonflies, mantis. Bees and bumblebees have a biting‑and‑licking mouth. Its elements are strong mandibles that allow biting and flattening food or other substances (e.g. wax), and a long, hairy tongue used to suck nectar and collect water. The suction mouth is found in butterflies and consists of a long, thin, spirally coiled suction proboscis used to collect liquid nectar.
Parasites such as mosquitoes, fleas, lice and aphids have a piercing‑and‑sucking mouth. It consists of a scissor‑like element (labella) that allows piercing the tissues of the host's body, as well as a suction and saliva tubes (labium) used to suck up liquids, e.g. blood, vegetable juices. The licking mouth of a fly is used for wetting and licking food. It consists of a tube ending with a tongue.
Legs and wings of insects
The legs of insects reflect their lifestyle. Cursorial legs are elongated and thin, usually ended with claws, sometimes pads that allow moving on flat, slippery surfaces (house fly). In grasshoppers, fleas and lice, the rear pair of thorax legs is adapted for jumping. Jumping legs are characterized by a strong elongation, a broad, muscular upper part and a relatively thin, slender lower part. Raptorial legs are found in mantis and dragonflies. They are always front, elongated, massive legs with a serrated inner surface, and are used to hold a prey. Some insects have very flattened legs. In a mole cricket, the front pair of legs is very wide and resembles a shovel. Additionally, they are equipped with numerous spikes and cloves, which are useful when digging underground corridors (digging legs). In water beetles and bugs, the rear legs are flattened. On their surface there are hairs that increase the surface of the legs and make them similar to a fin, which makes the insects swim well (swimming legs).
In crickets and grasshoppers, mainly in males, there is a vocal organ on the hindlimbs. Its rubbing allows making sounds. Explain the purpose of this action.
Wings allow insects to move in search of food and escape from predators. They are membranous skin folds that are a flight organ. In beetles and bugs, the first pair of wings is transformed into massive wing covers that have protective functions. Wings grow out of the thorax and usually occur in 2 pairs (butterfly), sometimes one (fly) or none (wingless insects). They are made of a membrane stretched over a network of tubes that give them their shape and stiffen them. Their colour can be defensive.
How do insects breathe?
Insects breathe using tracheatrachea – tubes of various diameters, which branch out, form a spatial system inside the body that also penetrates into the wings. From the inside, trachea are reinforced with chitin spirals that provide them with rigidity and maintain a constant patency of the entire system. The air enters them through spiraclesspiracles – small holes arranged on the sides of the body, and then goes inside the animal. Most insects pump the air into the trachea by rhythmically moving the abdomen. The trachea have closed ends filled with fluid in which respiratory gases dissolve. This is where the gas exchange takes place.
Sense organs
Insects most often have eyes composed of straight eyes, the number of which can reach up to 30,000. Each, regardless of the other ones, registers the intensity of light. The image is created in an insect’s brain as a result of the connection of signals coming from individual eyes. Hence, images that insects see do not have clear outlines and highlighted plans. Insects receive changes in light intensity, movement and colour in a wider range than the human eye. For example, they see an invisible part of the spectrum of light – ultraviolet. Insects with excellent eyesight, such as dragonflies, have short antennae that are mainly organs of the chemical sense: smell and taste, but also touch. The more branched they are, the more receptors they can fit, allowing an insect to receive odours from long distances. The male can sense the smell of a female from a distance of up to 10 km.
Reproduction and development of insects
Insects are dioecious.
Insects undergo complex development in which there are several larval stages. The larvae gradually transform into an adult (imagoimago). In some insects (grasshoppers, dragonflies, mantises or lice) the larvae resemble an adult form. However, they are smaller, usually have no wings and are not sexually mature. In their case we deal with incomplete metamorphosis. In the vast majority of insects (butterflies, beetles, bees, wasps, flies and fleas) the development proceeds with complete metamorphosis. Their larvae are not similar to the adult form. They eat a lot and often moult, stepping up the size of the body. After reaching the appropriate size, they are transformed into motionless chrysalischrysalis. In many insects, the chrysalis can be surrounded by a cocoon – a structure made of thin threads that are formed in special silk glands of the larvae. Inside the chrysalis, the larva transforms into an adult. This involves a complete re‑structuring of the body. Adult insects usually do not live long. They breed, sometimes take care of their offspring, and then grow old and die.
The butterfly caterpillar is a very ravenous larva. Within 20 days, it can increase its mass up to 10,000 times. Explain why it eats so much.
Find out which insects have and what are the differences between larvae such as caterpillar, maggot and grub.
The importance of insects
Insects are of great importance in nature. Many species of these animals, such as bees, bumblebees and flies, can pollinate most flowering plants, including crops important to humans. Without their help, these plants would not be able to produce fruit and produce seeds. Insects are also a source of food for many animals, mainly vertebrates, but also arachnids and other insects. Many of them feed on dead organic matter (e.g. many species of flies), manure of animals (e.g. dung beetle) or carrion (e.g. various species of beetles), which contributes to cleansing of the environment.
Herbivorous insects are usually perceived negatively by humans, because they cause huge losses in plant crops (e.g. cabbage periwinkle, potato beetle). Some species also eat stored food (flour millweed and grain weevil). Certain beetles, aphids and moths are plant parasites, and fleas, lice and bedbugs feed on animals and humans.
Many insects carry microbes that cause deadly diseases: mosquito – malaria, human louse – typhus, and tse‑tse fly – African coma. A human may also die as a result of a sting of a bee, a wasp or a hornet, if the person is allergic to venom.
Some insects provide valuable resources for humans. Bees produce honey, beeswax and putty, and mulberry silkworms spin cocoons from which silk is produced.
Insects that feed on other insects can be very useful for humans. Explain what they are used for.
Organize the development stages of the stick insect starting from the earliest one.
- egg
- imago
- larva
Assign the names of stick insect construction elements to the functions they perform.
excretion of manure, laying eggs, protection against water loss and injury, feeding, movement, receiving visual impressions, the place from which the crotch legs grow, the place where the most senses are embedded, receiving tactile sensations, taste, smell
| carapace | |
| legs | |
| atennae | |
| eyes | |
| mouth | |
| head | |
| thorax | |
| abdomen |
Summary
Insects are the largest group of animals.
Insects are arthropods that have a body covered with a chitinous cuticle, divided into a head, a thorax and an abdomen, 3 pairs of segmented legs, one pair of antennae and (in most cases) wings.
The structure of insects depends on the environment, lifestyle, type and manner of feeding.
Insects usually breathe using trachea.
Insects reproduce sexually, undergo complex development with complete or incomplete metamorphosis.
In the development with complete metamorphosis there is a still pupa and movable larva unlike imago.
Insects are an element of almost all food chains.
Keywords
arthropods, insects, larva
Glossary
aparat gębowy – przekształcone odnóża gębowe owadów przystosowane do pobierania pokarmu.
czułki – nitkowate, ruchome narządy zmysłów występujące u zwierząt bezkręgowych.
imago – postać dorosła owada.
poczwarka – nieruchome stadium rozwojowe owadów, które przechodzą przeobrażenie zupełne; poprzedza postać dorosłą; czasami pokryta jest kokonem z nici przędnych wyprodukowanych przez larwę.
przetchlinka – otwór w nieprzepuszczalnej powłoce umożliwiający wymianę gazową; występuje u niektórych stawonogów i roślin.
tchawka – system rureczek o różnej średnicy występujący we wnętrzu ciała owadów, pełniący rolę narządu oddechowego.