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 each have a little claw on the end.

Many caterpillars also have 5 pairs of prolegs, like Psalidostetha banksiae pictured above. The prolegs are not segmented, but are cylindrical stumps. 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. With 3 pairs of true legs and 5 pairs of prolegs, these caterpillars walk with a sort of ripple movement.

The larvae of other species of insects such as wasps and flies can have more than 5 pairs of prolegs.

full set of 3 pairs of true legs but with 7 pairs of prolegs :- Larva of a Sawfly, HYMENOPTERA (not a true caterpillar) Photo: courtesy of Jenni Horsnell, Wagga Wagga

Some species in different families have caterpillars with fewer prolegs. The number of prolegs is a constant throughout its life as a caterpillar, depending only on the species. These caterpillars move in a looper motion.

only 4 pairs of prolegs Caterpillar of Anomis flava, EREBIDAE

only 3 pairs prolegs Caterpillar of Chrysodeixis eriosoma, NOCTUIDAE

only 2 pairs prolegs Caterpillar of Scopula perlata, GEOMETRIDAE

Some have no prolegs at all, and move in a slug-like motion.

upside down Caterpillar showing no prolegs at all of Doratifera vulnerans, LIMACODIDAE

In the metamorphosis, in the pupa, all the prolegs disappear. However, the six true legs on the thorax are retained through pupation, and are transformed into the legs of the adult for most families of butterflies and moths.

butterfly with 6 legs
Troides euphorion : the Cairns Birdwing, PAPILIONIDAE

But, over the millenia of evolution, one pair of true legs has atrophied for the butterfly species in the family NYMPHALIDAE, so that they have only four legs, for example:

butterfly with only 4 legs
Danaus plexippus : the Wanderer Butterly, NYMPHALIDAE

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Caterpillar FAQS

Australian Lepidoptera

Australian moths

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(updated 11 April 2013, 23 November 2018, 26 May 2020)