A brief explainer
The word insect derives from the Latin word insectum, meaning “with a notched or divided body”, literally “cut into sections”, from the fact that insects’ bodies have three parts. Pliny the Elder created the word, translating the Greek word ἔντομος (entomos) or insect (as in entomology, which was Aristotle’s term for this class of life), also in reference to their “notched” bodies.
Insects are the most abundant multicellular organisms on planet Earth and are thought to account for more than 70% of all species. Insects are also among the most diverse groups of organisms in the history of life. Insects have been in existence for at least 400 million years, making them among the earliest land animals. Although, about one million species have been classified and named, their actual number is believed to range from 2.5 and 10 million.
Insects are a class of animals within the arthropod group that have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and two antennae. They are among the most diverse groups of animals on the planet: there are more than 1 million described species, which is more than half of all known living organisms. The total number of species is estimated at 6–10 million, and the class potentially represents over 90 percent of the differing animal life forms on Earth.
Insects may be found in nearly all environments, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.
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