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Excerpts from Jim Conrad's
Naturalist Newsletter
from the June 14, 2009 Newsletter, issued from the Siskiyou Mountains west of Grants Pass, Oregon:
A LONGHORN BEETLE'S SPECTACULAR AEDAEGUS
Once again I didn't know I'd taken a great picture until after it came onto my computer screen. See if you notice what's so spectacular about it in the above picture.
Look at what's issuing from the top beetle's rear end. When I saw that my first thought was that I hadn't known that beetles have penises. But, can that really be a penis?
With Bea in Ontario posting my picture on Bugguide.net where some experts helped out, I learned that the beetles are Dimorphic Flower Longhorns, ANASTRANGALIA LAETIFICA. With a little browsing I learned that the slender, cylindrical, wormy thing connecting the two beetles is an "aedeagus."
The aedeagus is a hardened, ringed sheath at the tip of which is a less hardened area, the "internal sac," which actually delivers sperm to the female. In the picture the internal sac is inside the female so all you're seeing is the aedeagus. When not copulating, the aedeagus and internal sac reside inside the male beetle but in preparation for sex the aedeagus "everts," or turns inside out, exiting the body to be what you see. Other insects possess aedeagi in different shapes and sizes; longhorn beetles in general have spectacular ones, and among the many species of longhorn beetles aedaegus sizes and shapes vary a lot.
But, is it a penis? Most specialists refrain from calling it that, but a few do. It depends on how you define what a penis is.
From the relative lack of information on Dimorphic Flower Longhorns and the few pictures of them on the Internet, I'd guess that they are relatively uncommon and of limited distribution.