Tuesday, June 30, 2009
I've been reading up on swallowtail caterpillars. Did you know there are five different caterpillar stages (called instars)? I didn't. I knew there were four developmental stages going from egg-caterpillar-pupa/chrysalis-butterfly, but I didn't know there were five sub-stages within the caterpillar stage. I kept wondering how all the different-looking caterpillars I found through Google Image Search could be the same species!
During the first and second instar stages, swallowtail caterpillars are dark brownish-black with yellow-orange spots, black spines and a white band around their middles. I saw some of these, but didn't get any pictures. I hope I get another chance to show them to you.
In the third, fourth and fifth instars, the caterpillars turn various shades of yellow, cream and green. I suspect the photos from yesterday are third instar caterpillars and today's photo is a fourth instar. Fifth instar is a pre-pupa stage, just before they form a chrysalis.
How do caterpillars go from first to fifth instar? They molt (shed their skins), just like a snake! Birdchick has some great information on her blog, including a video of a molt and pictures of caterpillars in various instar stages.