Insects, examples and characteristics of which we will present today, are the largest group of all creatures that inhabit our planet. It includes about 80% of the total number of animal species. More than 1,000,000 species have such a group as insects. Examples known to science are far from all species that exist in nature. Perhaps as much remains to be discovered. Many fossils and living primitive forms are described that clarify the evolution of the modern 29 orders into which insects are divided. Examples of modern species will be discussed in this article. Most fossil forms belong to the Lower Carboniferous (345 million years ago). At this time, extensive swampy forests were already inhabited by winged insects.
Ubiquitous animals
Even insects live in the sea. Examples of such species, however, are not numerous. Some of them stay on the surface, others live on the littoral, and one species lives even on the seabed. But wherever any other animals penetrate, insects certainly appear there either either as free-living forms or as parasites of other organisms. Insects are undoubtedly the dominant life form from the Arctic to the equator. Some of them live under snow and ice, others in the deserts, and others in salt lakes and hot springs. The world of insects is very diverse. In southern California, there is even a fly (Psilopa petrolei) that spends part of its life in pools of oil. One of the main reasons for the prosperity of insects is their ability to fly.
Ability to fly
With the exception of a number of primitive forms, most insects move freely in the air, which allows them to develop new habitats, elude predators, find partners and find food with greater ease than their wingless invertebrate relatives can do. Some of them even catch prey in the air. Although insects owe their prosperity to flight, the ratio of their body weight to wing area is such that theoretically they should not be flying. In fact, the muscles of their wings generate and realize energy with great speed. High sweep frequency compensates for insufficient lift.
The size of insects and their role in evolutionary prosperity
The size of insects also played an important role in their evolutionary prosperity. When they just appeared, about 350 million years ago, the conditions of existence were already reminiscent of the current. Insects have mastered until then ecological niches. This explains their relatively small sizes (although fossil dragonflies with a wingspan of up to 76 cm are known): they can survive and reproduce under conditions unfavorable for larger animals.
Primitive insects
It is believed that insects came from ancestors similar to millipedes, from which they differ mainly by the presence of only three pairs of limbs. Each pair is attached to one segment of the chest (middle body). The most primitive of modern species are those wingless insects, examples of which belong to four orders, united under the name Apterygota. All others have wings and are designated as Pterygota. Nail tails and beckless descended, probably, from creatures similar to two-tails, but both groups developed in different directions. The nails are characterized by a special fork on the abdomen, acting like a spring and allowing these animals to jump well. The bezyszagovye have no antennae, and part of their functions are the forelimbs.
Main groups and orders of winged insects
An important stage in the evolutionary formation of insects was the development of wings and ability to fly. Two squads - mayflies and dragonflies, whose representatives cannot fold their wings on their backs during rest, are combined into the Palaeoptera (Ancient winged) group. Insects with this ability form the Neoptera group (newwing). Seven units are considered the most primitive of the Neoptera. They are characterized by a fairly simple oral device. In addition, these are mainly herbivorous insects. Examples: earwigs (in the photo above), termites, cockroaches, praying mantises, etc. The springtime squad is a side branch with many archaic features. Squads of bug-like insects demonstrate a gradual improvement in the oral apparatus. It is primitive and non-specialized in hay eaters (pictured below) or developed stitching and sucking in bedbugs.
The remaining insect orders (Neuropteroidea) gained significant advantages over their more primitive relatives by improving the development cycle.
Incomplete and complete insects
Typically, all species from Palaeoptera and Neoptera are divided into two groups, depending on the development cycle. Insects with incomplete transformation (examples of them relate to Hemimetabola and Apterygota) are characterized by the fact that the hatching from eggs (juvenile nymphs) resembles adults. Later, after going through a series of links, nymphs become fully-formed adults. In insects with complete transformation (Holometabola), the larva hatched from the egg does not at all look like an adult.
This stage (caterpillar or vermiform larva) usually feeds on completely different food. The larva turns into a chrysalis, which can remain dormant for many months, and then through metamorphosis (tissue remodeling) turns into an adult insect. Differences in lifestyle between her and an adult allow them to use completely different habitats. 84% of the total number of insect species belongs to Holometabola, and many of them are of great economic importance.
Hymenoptera
Hymenoptera - an extensive squad representing the world of insects. They are characterized by the fact that the basic plan of their structure remains practically unchanged. However, these animals are significantly different from other insects with complete conversion. This is a rather isolated group, but according to the nature of larval development and metamorphosis, it draws closer to scorpion women.
Environmental adaptation
Coleoptera - the largest detachment in the animal kingdom - is characterized by the development of hard elytra, covering the rear pair of membranous wings, which are used for flight. The strength of the external skeleton and the adaptive capabilities of the basic plan of the structure turned out to be the leading factors in the development by adults of various habitats. The remaining insects with complete transformation are grouped around the once vast detachment of scorpion.
Butterflies are recognized by flake-covered wings and specialized mouth parts adapted for feeding nectar. The evolution of this detachment and some representatives of the diptera detachment proceeded in close connection with the evolution of flowering plants.
Caddis flies branched off from the butterflies, acquiring hair-covered wings and a chewing oral apparatus. Larvae lead an aquatic lifestyle. Two-winged flies fly with the help of the front pair of wings, and the second is turned into a ground beetle, playing the role of balance organs in flight. Diptera larvae exhibit greater adaptive specialization than other insects. Many adults feed on blood, which is due to their role in the transmission of infectious pathogens. Fleas are close to dipterans, they have no wings and the body is flattened from the sides. Together with a detachment of lice, this group is one of the ectoparasites of warm-blooded animals.
The problem of insect pests
Many evolutionarily advanced forms of insects from Holometabola often cause significant damage to humans. They can destroy crops or spread dangerous diseases. Among Hemimetabola such insects are not numerous. Examples (pests) are lice and locusts. But they cause great harm to humans. Only one species - desert locust (Schistocerca gregaria) - can cause hunger for more than 10% of the world's population. This insect (in the photo below) multiplies rapidly after heavy rains and, suddenly spreading widely, eats any greens in its path.
However, it must be said that basically insects are almost harmless. Moreover, they play their irreplaceable role in nature.
So, we examined such an interesting and large group of animals as insects. Examples, names, classification and characteristic features of them were presented in the article. We hope you enjoy reading it.