The variety of insects is enormous. There are those whose sizes are given in micrometers and whose body length is greater than that of dogs or cats. Because they are among the earliest animals to emerge, they have adapted to life in almost any environment. Millions of years of evolution have separated them so much that they share only a few anatomical features.
1
Insects are invertebrates classified as arthropods.
They are the most numerous group of animals in the world and may constitute up to 90% of this kingdom. To date, more than a million species have been discovered, and there may still be 5 to as many as 30 million undescribed species.
2
They share several anatomical features that allow them to be easily distinguished from other animal groups.
Each insect has a body composed of three segments (tagmas): head, thorax, and abdomen. Their body is covered with a chitinous carapace. Insects have three pairs of legs, compound eyes and one pair of feelers.
3
The oldest insect fossils date back 400 million years.
The greatest flourishing of insect diversity occurred in the Permian (299 - 252 million years ago). Unfortunately, the vast majority went extinct during the Permian extinction, the largest mass extinction ever to occur on Earth. The exact cause of the extinction is unknown, but we know that it lasted about 60,000 to 48,000 years. It must therefore have been a very rapid process.
4
The insects that survived the late Permian extinction evolved in the Triassic (252 to 201 million years ago).
It was in the Triassic that all orders of currently living insects arose. Today's insect families developed mainly in the Jurassic (201 - 145 million years ago). In turn, representatives of the genera of today's insects began to form during the dinosaurs' extinction period 66 million years ago. Many insects from this period are well preserved in amber.
5
They live in many different environments.
Insects can be found both in water, on land, and in the air. Some live in droppings, carrion or wood.
6
Insect sizes vary widely, ranging from less than 2 mm to more than half a meter.
The record holder, measuring 62.4 cm (24,5 in), is a representative of Spectra order. This specimen can be admired in the Chinese museum in Chengdu. Spectras are among the largest insects on Earth. In contrast, the smallest insect is the parasitic dragonfly Dicopomorpha echmepterygi, whose females (and they are more than half the size of the males) measure 550 μm (0.55 mm).
7
The size of currently living insects seems "just right" to us. However, if we moved back in time about 285 million years, we might get a shock.
At that time, the Earth was inhabited by giant dragonfly-like insects, the largest of which was Meganeuropsis permiana. This insect had a wingspan of 71 cm (28 in) and a body length of 43 cm (17 in). A fossil specimen can be seen in the Museum of Comparative Zoology at Harvard University.
8
Insects breathe using tracheae, to which air is supplied through spiracles.
Tracheae are protrusions of the insects' body walls that branch into a system of tubes inside the body. At the ends of these tubes are liquid-filled tracheae through which gas exchange occurs.
9
All insects have compound eyes, but some may have additional simple eyes.
There may be a maximum of 3 of these, and they are capable of recognizing light intensity but incapable of projecting an image.
10
The blood system of insects is open.
This means they have no veins, but hemolymph (which functions as blood) is forced by arteries into the body cavities (haemocoels) surrounding the internal organs. There, gas and nutrient exchange occurs between the hemolymph and the organ.
11
Most insects reproduce sexually and by laying eggs.
They are fertilized internally using external genitalia. The design of the genitalia can vary significantly between species. The fertilized eggs are then laid by the females using an organ called an ovipositor.
12
There are also insects that are oviparous.
Examples of such insects are the beetle Blaptica dubia and the fly Glossina palpalis (tse-tse).
13
Not all insects undergo a complete transformation.
There are three developmental stages of an incomplete transformation: egg, larva and adult (imago). In the complete transformation, there are four stages: egg, larva, pupa and adult. Complete transformation occurs in hymenoptera, caddisflies, beetles, butterflies and flies.
14
Some insects have adapted to living alone while others form huge communities, often hierarchical.
The most common solitary insects are dragonflies, less commonly beetles. Insects that live in groups include bees, wasps, termites, and ants.
15
No insect can kill a person with its bite, but this does not mean that such a bite will not be unbearable.
The most venomous insect is the Pogonomyrmex maricopa ant, which lives in the southwestern United States and Mexico. Twelve bites from this ant can kill a 2 kg rat. They are not fatal to humans, but their bite causes extreme pain lasting up to four hours.
16
The most numerous insects are beetles.
More than 400,000 species of these insects have been described so far, making up about 40% of all insects and 25% of all animals. The first beetles appeared on earth between 318 and 299 million years ago.
17
At least 66 species of insects have gone extinct in modern times (since 1500).
Most of these extinct species inhabited oceanic islands. The factors posing the greatest threat to insects are artificial lighting, pesticides, urbanization, and the importation of invasive species.
