Caterpillars of different families have different numbers of legs. The number of legs is a constant throughout its life, depending only on the species. All Caterpillars have 3 pairs of true legs attached under the thorax. The true legs are segmented, with joints like our knees and ankles. They have a little claw on the end.

close-up of Opodiphthera eucalypti caterpillar,
showing claws on true legs, and crochets on prolegs,
(Photo: courtesy of Jan MacDonald, Finch Hatton, near Mackay, Queensland)

Most caterpillars also have up to five pairs of prolegs. The prolegs are not segmented, but are cylindrical. They are used for walking and clinging, as they have a set of microscopic hooks on the base (crochets). The last pair of prolegs on the anal abdominal segment are usually called claspers.

So in all, they have 16 legs: they are hexadecapodal.

full set of six true legs and ten prolegs :- Caterpillar of Danima banksiae, NOTODONTIDAE

The larvae of other species of insects such as wasps and flies can have more than 16 legs.

full set of six true legs and fourteen prolegs :- Larva of a Sawfly, HYMENOPTERA (not a true caterpillar) Photo: courtesy of Jenni Horsnell, Wagga Wagga

The Caterpillars of some species have atrophied prolegs, and appear to only have 8, 6, or 4 prolegs, or even no legs at all.

	only eight prolegs:- Caterpillar of Anomis flava, NOCTUIDAE
	only six prolegs:- Caterpillar of Chrysodeixis eriosoma, NOCTUIDAE
	only four prolegs:- Caterpillar of Scopula perlata, GEOMETRIDAE
	no legs at all:- upside down caterpillar of Doratifera vulnerans, LIMACODIDAE

The 6 true legs on the thorax are retained through pupation and are transformed into the legs of the adult. However, in the metamorphosis, the all prolegs disappear. Also, one pair of true legs may disappear, so that many butterfly species have only four legs, for example:

butterfly with only 4 legs
Danaus plexippus : the Wanderer Butterly, NYMPHALIDAE
(Photo : courtesy of Fred Swindley)

Link to
Frequently Asked Questions about Caterpillars

Australian butterflies

Australian caterpillars

Australian moths