Recognising a caterpillar is not always straightforward: many insect larvae look similar but are not caterpillars. The word caterpillar refers exclusively to the larval stage of butterflies and moths (Lepidoptera). Maggots are fly larvae, “white grubs” are beetle larvae, and some myriapods (millipedes) can also be confusing at first glance. To identify a true caterpillar with certainty, the simplest and most reliable criterion is the number of legs.
The main criterion: the number of legs
A caterpillar has:
- 3 pairs of true legs near the head (as in all insects),
- up to 5 pairs of prolegs (suction‑cup–like false legs), with the last pair often slightly separated from the others.
Diagram of caterpillar legs (3 true + 5 false).
The exception: geometer caterpillars
Caterpillars of the geometer family have only 2 pairs of prolegs instead of 5. They move by looping their body, which gives them the nickname inchworms or loopers.
Geometer caterpillar — only 2 pairs of prolegs.
What looks like a caterpillar… but isn’t one
Several larvae are often mistaken for caterpillars. Here is how to tell them apart:
__Chafer or rose‑chafer larvae:__ white curved body, short legs near the head, no prolegs.
__Millipedes (myriapods):__ many pairs of legs along the entire body.
__Sawfly larvae:__ similar to caterpillars but belong to the Hymenoptera. More than 5 pairs of prolegs.