Insects are animals typically recognized by their six legs and two pairs of wings. Despite a remarkable diversity of shapes, colours, and adaptations, their bodies are always divided into three parts: the head, the thorax, and the abdomen.
The insect world, however, is full of exceptions: some species have no wings, others have no eyes… And an insect in its larval stage can look completely different from the adult.
As arthropods, insects have jointed legs and are covered by an exoskeleton, which protects them from impacts and prevents desiccation (dehydration).
The insect: a three-part body
Despite their often tiny size, insects have a remarkably sophisticated body plan.
The head: A centre of perception
The head of an adult insect varies in complexity, but it generally includes three main components: the eyes, the antennae, and the mouthparts.
The compound eyes, made up of a large number of ommatidia (light-sensitive receptors), often take up much of the head. These receptors allow insects to detect even the slightest movements. One eye alone may contain several thousand ommatidia. Many species also have two or three simple eyes, called ocelli, which are often the only type of eyes found in larvae.
The heads of adult insects also bear a pair of antennae, whose shape and size vary among species. Antennae are used to perceive smells, vibrations, and other environmental cues.
The mouthparts, usually located on the underside of the head, differ greatly from one group of insects to another, depending on their way of life.
The thorax: the insect’s power centre
The thorax is made up of three segments, each bearing a pair of legs. The second and third segments also carry the wings, whose shape, size, and texture vary across insect groups and orders.
Most species have four wings, but some, such as silverfish, fleas, and lice, lack them entirely. Flies, meanwhile, have only two.
The abdomen: a vital core
In most insects, the abdomen is the most flexible part of the body, allowing it to expand during feeding. It contains essential organs, including the digestive system, the heart, part of the respiratory system, and the reproductive organs.
An ingenious anatomy
Every part of an insect’s body (the head, thorax, and abdomen) performs essential functions that allow it to see, sense, move, feed, breathe, and reproduce. This remarkably efficient architecture helps explain the evolutionary success of insects, the most diverse group of animals on Earth.
An unusual way to breathe
Insects have neither noses nor lungs. Instead, air enters their bodies through a series of tiny openings along the sides of the abdomen called spiracles. From there, it travels through a network of rigid tubes known as tracheae, delivering oxygen to even the smallest corners of the body.
An open circulation system
An insect’s heart is shaped like a long tube lined with tiny openings. Its blood, called hemolymph, is often clear, yellow, or greenish and flows freely throughout the body.