Caterpillar Anatomy

Swallowtail caterpillars have an organ just behind the head called an osmeterium. When it is bothered, the caterpillar turns a sort of pocket inside out, and these orange "horns" are pushed out and then withdrawn again.

The horns emit a real stink (reminding me of marigolds). Apparently this lets birds know that the caterpillars taste bad. One of our books (Anna Comstock's Handbook of Nature Study has a unit on the Black Swallowtail) states that this protection is why they don't hide under leaves.

I've been trying to get a good photo of this phenomenon, but had no luck until today. Becca found a caterpillar outside in the parsley patch (the one that escaped during cleaning?) and we poked it a bit...for educational purposes, of course.

There was some discussion of bringing this guy into the habitat, but we've got several making chrysalises already (posting tomorrow I hope), so I decided not to be greedy. Besides, it will be fun to see if we can find this one's chrysalis outside in a few days--a real nature hunt.