Which of the following is NOT an insect?

The correct answer is that a slug is not an insect. Slugs belong to the class Gastropoda, which includes snails and slugs. They are mollusks, characterized by a soft body and lack of a hard shell, unlike insects, which are classified under the class Insecta. Insects are defined by their three-part body structure (head, thorax, abdomen), a pair of antennae, and typically three pairs of legs, features that slugs do not possess.

On the other hand, crickets, centipedes, and earwigs all fall under the category of arthropods. Crickets are insects, known for their jumping ability and distinctive chirping sounds. Centipedes, while not classified as insects, are still arthropods under the class Chilopoda, known for their elongated bodies and many legs. Earwigs are also insects, characterized by their pincher-like appendages at the rear. This distinction helps clarify why the slug is the only choice that does not belong to the insect category.