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How many legs is enough?

January 19, 2023

There are creepy crawlies out there with many legs. Centipedes (from the Latin centi meaning hundred and pedis meaning foot) and millipedes (from the Latin milli meaning thousand) do not literally live up to their names, but they certainly have many pairs of legs.

But how many legs does a caterpillar have (see photos)? Being insects caterpillars have six legs but appear to have a lot more. The six ‘true’ legs are those situated on the thorax near the head. The other leg-like appendages are called prolegs and are used for walking and clinging.

Most caterpillars have a pair of anal prolegs (known as claspers) at the end of their bodies and several pairs of medial prolegs half way down their bodies. Each proleg contains a series of hooks. When the caterpillar is moving fluid is pumped into the proleg to expand the hooks. Once the proleg hits the surface the fluid pressure is released and the hook closes attaching the caterpillar to the surface.

For caterpillars the difference between a ‘true’ leg and a proleg is that the former is jointed into five segments whereas the proleg is a fleshy structure with minimal musculature.

Other insect larvae also have prolegs. The larvae of sawflies (called spitfires) have prolegs on each abdominal segment, a minimum of six pairs.

Imagine tying your shoe-laces.

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