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.


  1. Caroline,
    I'm so disappointed, we have not had a single butterfly in our garden this year and I have only seen one humming bird. Where are they? I'm glad that you are able to enjoy them. :-)--Randy

  2. Randy, we've had more caterpillars than butterflies and we've only had two hummingbirds. Perhaps it's too hot for the hummingbirds to hang around here. We usually get butterflies later in the summer.

  3. Very interesting post. I try to keep fennel around for the butterflies--the caterpillars have mowed it to the ground this year!

    I think we have the areas hummers in our garden! I have counted 8 all vying for the same feeder! Yesterday one staked his claim on it, sitting on it and chasing away all the others. More fun than watching TV!

  4. I have several on my parsley plant and must heck which stage they are at. I would love to see them pupate. Thanks for the information.