September 20, 2013

Addendum to the Cat Post!

This week we've seen and photographed some more cool caterpillars and a couple of things seemed worthy of posting. 

In my last blog entry I showed several swallowtail caterpillars: Black, Spicebush, Giant and Pipevine. One of the most interesting things about swallowtail cats is that when disturbed, they extrude (I think that "evert" is actually the proper term) a weird  fork-shaped organ from their head that not only looks scary but smells terrible--I told you it was weird!  This defensive organ is called the osmeterium, and the foul-smelling compounds vary from species to species. 

Until this week we had never seen this, but the other day we got a few shots of a very annoyed Black Swallowtail caterpillar. Here is a series of pictures, showing the caterpillar going from placid to really mad:

A bird or other predator not only gets the scary visual, but gets a whiff of really bad smelling chemicals.

The same day when we were out at Siebenthaler Fen we finally saw the caterpillar of the Eastern Tiger Swallowtail. A sharp-eyed friend that we were with spotted it on an ash leaflet, and the color of the caterpillar perfectly matched the color of the leaflet. Eastern Tiger Swallowtails are relatively common, but we had never seen the larva. Talk about a strange looking animal!

That eyespot is just a marking and not its actual eye. In contrast to the other swallowtails, Eastern Tiger Swallowtails feed on a wide variety of plants, including tuliptree, ash, and wild black cherry and several others. Earlier instars of this caterpillar are bird-dropping mimics, while this later form is thought to resemble a snake. In any event, I'm glad we were able to see and photograph it. I sort of wish we had been able to see it evert its osmeterium, but repeated photographs were probably enough disturbance for one day!


  1. New Verb: To evert an osmeterium.... learning something new all the time from you! Thanks.

  2. Ha! It is certainly new vocabulary for me too! It is so fun to think of all these critters going about their business in such strange and varied ways!