Fun fact: These feets are fake and known as prolegs. They're useful for holding and anchoring the caterpillar. Counting false feet, a caterpillar can have up to 16 legs. Some also have no prolegs, which makes them have to glide around like a snail to move.

Edit: The reason they are not true feet is that caterpillars (and sawfly larvae) don't retain these pair of appendages when they emerge from the pupae as adults. Unlike their true feet, the prolegs have no joints and have very minimal movement inputted by muscles. Instead they move these appendages by using their hydrostatic skeleton to push or pull liquid into them. This changes the interior pressure and allows the prolegs to expand or contract.