Unknown beach beetle
July 17, 2009
These beetles were discovered during horseshoe crab spawning season on Pickering Beach, Delaware. I’ve yet to find a good match in any of our bug books. We did collect one that looked very dead, but it crawled inside a crab carcass and hasn’t been seen since. Can you help with an ID?
I’ve been visiting periodically since last July when I identified and observed a grapevine beetle from July through the end of November.
Pickering Beach, Delaware
Were it not for the antennae on the individual on the far left, we would say that these are Carrion Beetles, more specifically, the Northern Carrion Beetle, Thanatophilus lapponicus. BugGuide has several images including some mounted specimens. One photo of a specimen from Alberta Canada is a dead ringer, but for the antennae. The individual in your photo on the far left most certainly has lamellate antennae which Comstock in our 1940 edition on page 41 defines as “the segments that compose the knob are extended on one side into broad plates.” On page 487 of the same volume under the family Silphidae, he writes: “The segments near the tip of the antennae form a compact club, which is neither comblike nor composed of thin movable plates; sometimes the antennae are nearly filiform.” Finding these beetles during the spawning of the horseshoe crab might be significant. Since Carrion Beetles are attracted to putrefying flesh, and since there is probably a bit of carnage during the mating, the presence of Carrion Beetles makes sense. Since we have pretty much decided that this if probably NOT a Northern Carrion Beetle, based on the antennae alone, we are stumped. The lamellate antennae are often found in the Scarabidae, but we aren’t happy with that ID either. We are forwarding this mystery to Eric Eaton to clean up. As a side note, we are thrilled that your photo includes what would seem to be a mating pair in the center, which qualifies this image for our Bug Love page.
Immediately upon posting we decided to do additional research. We backtracked to the superfamily Scarabaeoidea that includes both Scarab Beetles and Carrion Beetles. There we found the family Trogidae, the Hide Beetles. We found our match, antennae and all, and now we need to try to determine the genus. Our frontrunner is Omorgus scabrosus, based on the drawing of the scutellum by Phil Harpootlian on the family page on BugGuide. That would make this a Hastate Hide Beetle. Since they are found on carrion in the late stages of decomposition, all that we stated earlier regarding the presence at the Horseshoe Crab spawning holds true. Since our archiving taxonomy is sketchy at best, we will be filing this with the Carrion Beetles.