Moved from Anise Swallowtail.

The younger caterpillars (early instars) are colored presumably as bird droppings, though we don't know if anyone figured out a way to test that! The older instars take on the familiar green and black bands. Swallowtails generally lay only a few eggs at a time and scatter them about. You may be seeing the progeny of several different females who deposited eggs at different times. So you get to see all the various ages of the caterpillars at the same time. Every time they've eaten enough to grow, they need to shed their old exoskeleton, and the new one is a different color or form. Will be interesting to see if you get the opportunity to see any of them shed.