Danaus plexippus - day 4

I was reading a bit about caterpillar anatomy, so I got the little critters out and tried to spot some things. I'll throw out a few terms.

Here you can see two little knobs on the cat's head. At first I thought they were little spines, but they are actually the beginnings of the cat's front tentacles - simple sense organs. The back tentacles are even less obvious at this early stage.

In this photo it is possible to distinguish between the 3 pairs of "true legs" on the caterpillar's thorax, and the 5 pairs of "prolegs" on the abdomen. You can barely possible see, on the body segments holding the first couple of prolegs, the tiny holes called "spiracles" through which the caterpillar breathes.

The dark setae covering the caterpillar can be seen pretty clearly in this photo. If you compare them with those present on the older (by 2 days) cat in one of the images above, it appears that they become shorter as the cat gets older. The cats are all so small right now that it is virtually impossible to make out any other details on the head.


My source for terms, etc and a fantastic resource about Monarch cats is "A Field Guide to Monarch Caterpillars (Danaus plexippus)" by Karen Oberhauser and Kristen Kuda - Illustrations by Kristen Kuda, Department of Ecology, Evolution and Behavior; University of Minnesota; 1987 Upper Buford Circle; St. Paul MN 55108. It's available online as a pdf - a quick search should turn it up. There's quite a bit of useful info crammed into 16 pages.