A worm is not classified as an insect because it does not contain the characteristics defined by the scientific classification system for insects. Worms are tubular and do not contain legs or properly segmented bodies, two characteristics needed for an insect classification.
The scientific classification system defines an insect as having:
- Three pairs of legs
- A segmented body in three parts (head, thorax and abdomen)
- One pair of antennae
- Often, a pair of wings
Some insects have adopted the worm name including inchworms, glowworms and silkworms, but they do not have the characteristics of an actual worm.
A commonly known worm is the earthworm, which is found in gardens and most backyards. Its tubular body and lack of legs, antennae or proper body segments is descriptive of all types of worms, although some worms do have mouths.