Mystery Exuvia

January 20, 2011 | Armonia Nature Preserve, Limon Province, Costa Rica

What do you make of this exuvia? I found it just like this, sticking out of a large downed tree spanning a small creek.

Not sure if you can tell, but there’s a few small horns on the side and then one larger forked horn extending out from the bottom. Whatever left it squeezed out through a split on the top.

It measured 10mm in diameter, and there’s about 18mm extended out of the tree. I carefully pulled the rest out, and it measured 45mm long overall.

The whole thing

Even the rear end is somewhat bizarre looking.

Rear end

Ever seen anything like it? Any guesses as to what left it? A beetle perhaps?

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4 Responses to Mystery Exuvia

  1. As far as I can tell, all or nearly all beetles have exarate pupae – this highly modified form suggests maybe Diptera? I’ve seen tabanid and mydid fly pupal exuviae protruding from dead tree trunks with weird spikes and spines on the front end.

    • Troy Bartlett says:

      Thanks for the tips, Ted. I had to look up “exarate”, but now I understand what you mean. I hadn’t considered Diptera. I skimmed the Diptera section of “How to Know the Immature Insects”, but I didn’t see anything similar. I’ll keep digging. The large size and odd appearance of this exuvia really have me intrigued.

  2. Fernando Carvalho Filho says:

    It is a timber fly (Pantophthalmidae)puparium. The larvae feed by boring into living wood.

    • Troy Bartlett says:

      That’s awesome, thanks! Hopefully, I’ll get an opportunity someday to photograph an adult, described elsewhere on the web as “large and robust”. Indeed!

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