meloidae

I am impressed. Several of you* figured out the mystery behavior: reflex bleeding, a defensive response employed by some arthropods with especially nasty hemolymph to deter predators. A couple of you even pegged the identity of the mystery arthropod, a blister beetle in the genus Epicauta. Here's the uncropped photo: An Epicauta blister beetle reflex bleeds when grasped with forceps. Five points each to Tim, Ainsley, Neil, and Dave. And, ten points each to Pete and TGIQ. So. Um. Don't spend them all in one place... Posing on a mesquite flower. *what's up with all the guessers-of-mysteries…
Nemognatha Blister Beetle, California. Some of the oddest blister beetles in western North America are in the genus Nemognatha.  Their mouthparts have become elongate to form a proboscis- a common trait among other groups of insects- but rare among the beetles.  They are commonly seen on flowers feeding on nectar. Nemognatha with associated Notoxus beetles, Nevada. photo details: Canon MP-E 65mm 1-5x macro lens on a Canon EOS D60 ISO 100, 1/200 sec, f/13, flash diffused through tracing paper
Epicauta pardalis - spotted blister beetle Tucson, Arizona Here's a beetle so toxic it can kill a horse. The horse doesn't even need to ingest the beetle, it just needs to ingest something that the beetle bled on.  Blister beetles produce the defensive compound cantharadin- the active ingredient of the aphrodesiac Spanish Fly- which they reflex-bleed out their joints when threatened: photo details (top) Canon 100mm f2.8 macro lens on a Canon 20D f/13, 1/250 sec, ISO 100, indirect strobe in white box. (bottom) Canon MP-E 65mm 1-5x macro lens on a Canon 20D f/13, 1/250 sec, ISO 100, flash…