Mystery Beetles

January 18, 2011 | Gandoca-Manzanillo NWR, Limon Province, Costa Rica

The day I spent in Gandoca-Manzanillo National Wildlife Refuge, I encountered many beetles like the one above. They were always crawling around on large leaves. I didn’t observe them feeding or see any obvious damage from possible feeding in their vicinity. Rather, I spotted what I assume are both males and females, possibly coming together for mating. I didn’t actually see any mating though.

I suspect the one above is a male, based on those antennae. Here’s what I figure is a female. There’s also a bit of its frass there (confirmed from another image).

Female?

There’s some variability in the coloring as well. Here’s another male, with less black on the head and pronotum.

Another male, with less black

I wished I could say more about their identity. My initial impression was Lycidae. Doesn’t seem quite right though, with no obvious latticework of veins on the elytra and such an exposed head. I looked through my North American beetle references, but nothing seemed like an obvious fit. Elateridae? Eucnemidae? Pyrochroidae? Hopefully a beetle expert will be able to at least place these in a family for me.

Here’s one more view of those antennae from the same individual as the lead photo.

Another view of those antennae