At this point our 89 caterpillars are in all stages of larval development. Like people, they grow at their own rate and in their own time; the entire process from egg to adult butterfly taking about a month. As the caterpillars grow and become too big for their own skin they molt, much like a snake does. Between molts, the phases are called instars. Monarch caterpillars have 5 instars in total.
Because they quickly eat their shed skin (it is a rich source of vitamins) before further munching on Milkweed, it is hard to tell when caterpillars have moved into a new stage, but there are other indicators. For example, their color becomes deeper and more rich through each adjustment, they grow thicker antennae to help them find food (although they have 6 pairs of simple eyes their sight is still poor), and more established prolegs, or feet, to better help them grip the Milkweed leaves. Time in each instar stage can range between 1 and 5 days, although it varies with the temperature and light availability. We expect ours to take a little longer to develop because they are being reared in our cooler office climate! At this point we have transplanted the largest of the bunch into a rearing net as they get ready to move into their pupa stage. Check them out in their new digs!