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Insects and other arthropods

What is an insect?

English
Dorsal view: The elytra, or hardened forewings, of this firefly cover part of the thorax and abdomen.
Photo: Insectarium de Montréal (Mélanie Riverin)

At the adult stage, insects’ bodies are divided into three parts: the head, thorax and abdomen. It has three pairs of legs and often has wings. If you keep these characteristics of insects in mind, it’s easy to tell them apart from other arthropods.

However, the insect world is full of exceptions – some species don’t have wings, others have no eyes… As well, an insect’s larval stage and its adult stage can be very different.

A strange way of breathing

Insects do not have a nose and lungs for breathing. Air enters through a series of small holes on the sides of their body called stigmata. Air circulates through their bodies via a network of rigid tubes called tracheas.

Free circulation

An insect’s heart is shaped like a long tube with tiny openings. Insect blood is called hemolymph. This liquid is often clear, yellowish or greenish, and circulates freely through the insect’s body. Insects do not have veins.

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