This Insect Has an Unfathomable 4,000 Muscles. See How it Moves.

What you see here isn’t an animation from Pixar’s A Bug’s Life. This is a close-up of a swallowtail caterpillar, taken by @schwalbenschwanz.schweiz photography. This macro shot of the caterpillar shows its tiny little legs in action, which you might find surprising. Instead of having feet, caterpillars move by gripping their legs in this undulating motion. However, they also have hidden legs that you don’t see.

Caterpillars Have Complicated Limbs

From a distance, you’d never be able to tell that this caterpillar has such a complex leg system. Its movements are small and subtle, akin to snakes squirming across the ground. It’s not until it makes a vertical climb that you can see everything going on beneath that bulbous body. In this video, you can see several pairs of leg-like appendages known as prolegs. These tiny “feet” are responsible for most of their movement, which most caterpillars use on the ground and plants. Depending on the species, these tiny legs extend downward from the caterpillar’s abdomen and can range from two to five pairs. Caterpillars use these prolegs like you might climb a wall: by moving one hand first, then the other, then one foot, and then your other. As one pair of prolegs detaches, another attaches, functioning as built-in carbines.

In addition to these prolegs, caterpillars also have six true legs. While these don’t help with regular movement, they are used as suction cups when climbing. A swallowtail caterpillar such as this one uses its true legs to secure itself to various surfaces. Once secured, it can do things like eat, rest, or drink. You’d never guess it, but caterpillars have more body muscles than you think. Each insect has 4,000 muscles that it uses to move, with each segment having 70 muscles alone.

Prolegs Are Lost During Metamorphosis

When a caterpillar undergoes metamorphosis, it sheds its prolegs in favor of wings. Its legs are shed with the rest of its round body, and true legs grow in their place. While much of metamorphosis is still a mystery to scientists, what happens physically inside a pupa is not. As the caterpillar sheds its former body, it and its prolegs become mushy within the chrysalis. As time passes, this substance regrows into the butterfly that eventually emerges.

For this swallowtail, the process could take weeks to months, depending on environmental conditions. The butterfly takes less than a minute to emerge from its chrysalis. While its wings are fully developed, a swallowtail can’t fly immediately and must wait several hours for its wings to harden. By the time it’s ready to take off, it will have become familiar with the six legs that have replaced its prolegs.