How to Manage Pests

How to distinguish insect larvae

A larva is the immature stage of an insect that develops through complete metamorphosis, those with an egg, larva, pupa, and adult life stages. Larvae of many types of insects can easily be confused. However, caterpillars (larvae of butterflies and moths, Lepidoptera) that feed or occur openly on foliage generally can be distinguished from openly feeding larvae of beetles (Coleoptera), larvae of sawflies (a type of wasp, Hymenoptera), and true flies (Diptera) by the number and arrangement of prolegs (leglike appendages) on the abdomen and whether true legs (three pairs on the thorax) are present.

Identification

• Sawfly larvae that feed openly on foliage have pairs of prolegs on six or more abdominal segments.
• Caterpillars have proleg pairs on five or fewer abdominal segments and three pairs of true legs.
• Beetle larvae such as those of leaf beetles have no prolegs, but they do have true legs.
• Fly larvae lack true legs, as illustrated here by a predatory syrphid. They have fleshy protuberances on their abdomen or on both the abdomen and thorax.

Caterpillar-like larvae found feeding openly on foliage can generally be distinguished by the number and location of prolegs (leglike appendages, or fleshy stubs) on the abdomen and whether true legs are present.