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