After 4 to 10 days inside the egg, a tiny caterpillar hatches out. The hatchling is only about 2mm long.
The hatchling starts out tiny, but, over the next 9 to 20 days, the caterpillar grows to many times that size – up to about 4cm long! To grow so much, it has to eat – and they sure can eat! As the caterpillar eats and grows, it gets too big for its skin. It sheds its skin to reveal a new skin underneath. Each time it sheds, it starts a new stage called an instar.
The tiny hatchling is a first instar caterpillar. Often, its first meal is the shell of the egg it just hatched out of. Then it starts to eat the leaf it is sitting on, nibbling at the surface of the leaf. The first instar is quite pale – its stripes are barely visible.
After 2-4 days, it sheds its skin the first time, and the caterpillar becomes a second instar, with more noticeable stripes and tentacles at each end of its body. It now tends to eat the swan plant leaves along the edges.
A few days later, it sheds its skin again to become a third instar, and so on. Each time, the caterpillar gets bigger and hungrier!
The fifth instar is an eating “machine”! It can gobble 5 or more swan plant leaves a day. If you have a lot of fifth instar caterpillars on your swan plants, your plants can get eaten very fast. The fifth instar caterpillar is the one that forms a chrysalis. It eats a lot to store up energy for turning into a butterfly.