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Insects and other arthropods

What is an arthropod?

Woodlouse, Québec, Canada.
Photo: Insectarium de Montréal (Claude Pilon)
Woodlouse, Québec, Canada.
  • Woodlouse, Québec, Canada.
  • Archispirostreptus gigas.
  • Hadrurus arizonensis, United States.
  • Poecilotheria regalis, India and Sri Lanka.
  • Phyllium sp., Philippines.
  • Snail, Québec, Canada.
  • Earthworm, Québec, Canada.

For many people, all tiny creatures such as slugs, worms, millipedes, woodlice, ladybugs or ants all fall into one category – bugs! However, when we take a closer look, we learn that they are not all the same. Some are insects, others are not. With just a little knowledge, it becomes easy to recognize them.

Like woodlice, millipedes, spiders and scorpions, insects belong to a very large group of animals called arthropods. They are called arthropods because they have articulated legs in the adult state (arthropod means “articulated foot”). And, like other arthropods, the species that belong to the insect class have an exoskeleton, or external skeleton. The exoskeleton is a sort of shell that protects against shock, injury and dryness. Arthropods are part of the group of invertebrates because they have no spinal column.

Other tiny animals are not arthropods. Earthworms have bodies composed of many segments, but have no legs. They belong to the phylum Annelidae. Snails, whose bodies are not segmented, are mollusks.

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