Monarch caterpillar with head capsuleThe Monarch caterpillars are munching away on milkweed at the Youth Services desk.

When they arrived they were the length of a fingernail. Now they’re over an inch long. Their main job right now is to grow. As their bodies get bigger, they molt, or shed their skin. They will do this five times. The time in between molts is called an instar. Our caterpillars are probably on their third and fourth instars. By the time the caterpillars are fully grown, they will be 3,000 times bigger than when they hatched!

This photo shows one of our caterpillars soon after molting. The stripped black oval is its head capsule, the skin it just shed from its head. The caterpillar’s new skin is soft. It will harden up to provide support and protection. As it hardens, the familiar yellow, white, and black strips will return.

We expect that the caterpillars will be nearing their pupa (chrysalis) stage by the beginning of next week.

Our caterpillars love visitors! Please stop by for a visit the next time you’re in the library.