Subject: strange beetle?
Location: Portland Or.
May 26, 2012 12:24 am
I took this photo today in Selwood Or. near Portland close to the Willamette River. When I got home and looked it looked like it was sunning it’s self after moulting…
This is a Longhorned Borer Beetle in the family Cerambycidae and we believe it is Synphaeta guexi, sometimes called the Spotted Tree Borer according to this BugGuide posting. It does appear from your photo that the beetle might have just metamorphosed and that the pupal exuvia is to the left of the beetle. If that is the case, we are very curious to get the opinion of an expert. We thought that the metamorphosis occurred in the pupal chamber within the wood and that the adult then chewed its way to the surface. The larvae of Longhorned Borer Beetles are found in wood and they are often very specific about the trees that they bore into. Do you happen to know what kind of log this was? Also, do you have a dorsal view that might help confirm the identification. This comment is also posted on BugGuide: “this is indeed an uncommon beetle that seems to consistently evade experienced insect enthusiasts: ALL of its images we have on BG to date have been posted by first-time contributors!” We will try to get an opinion from Eric Eaton.
Unfortunately that is the only image I captured. I meant to mention that it was almost 2 inches long which is why I noticed it. It was on a very old bit of railing on a footbridge so if it was a specific kind of wood I have no idea. I would like to think I could go back the next day but I am sure it is gone now. If there is any more info I can provide I would be happy to do that.
Thanks for the update Jamie. If it was found on a bridge, then that tends to discount that the pupal exuvia is the object to the left of the beetle. That might just be some random tree debris. Our belief that the metamorphosis occurs beneath the surface and that the adult chews its way to the surface can persist unchallenged.
Eric Eaton confirms identification.
Yes, it is. The beetle may have been struggling to free itself from the pupa as it also worked its way out of the log.