Bug tracker, at your service.

Okay, I might as well make it official.  Ever since my book, Tracks & Sign of Insects and Other Invertebrates, was published, people have been sending me photos of strange and wonderful things and asking me what they are.  I thought it would be nice to have these exchanges in a public place, so that everyone can benefit from whatever I’m able to figure out.  Here is my favorite so far, from William Lee, who found this object attached to a leaf in a forest in Singapore:

A mysterious cocoon from Singapore, photographed by William Lee.

Another view of the same cocoon.

And my response:

What a beautiful structure this is. I have not seen this before, but I can tell you a few things about it: In the top photo, the skin of a caterpillar is visible at the bottom of the cocoon, so that is who constructed it. The cocoon appears to be made largely, if not entirely, of the caterpillar’s hairs, rather than of silk. When I zoom all the way in, I can make out the little barbs on the hairs, which no doubt help to hold the cocoon together. In North America, the caterpillars that do this are in the family Erebidae–either tiger moths (Arctiinae) or tussock moths (Lymantriinae). However, I don’t know of any that make a perfect square mesh structure like this. Normally, collecting a cocoon and waiting to see what emerges is a good way to find out what made it, but that wouldn’t work in this case: the object suspended in the middle is the puparium of a parasitoid fly (probably a tachinid). The fly larva developed inside the caterpillar, then devoured it once the cocoon was finished, and it is now transforming into an adult fly within the shelter of its host’s cocoon.

If anyone has any more information about this cocoon, please chime in!  And if you have a mystery of your own you’d like me to take a crack at, please send it my way!