Subject: Nightime beetles
Location: Pátzcuaro, Michoacán, México
May 14, 2014 9:47 am
These small brown beetle-like bugs vanish during the day, but are out after dark by the hundreds, merrily chewing the leaf margins on various plants. Their favorites seem to be oregano, honeysuckle, rose, the tender flowers of cana lillies, and avocado. They seem to prefer young leaves. Often they are stacked one atop another as if they are mating. They only appear at our house in late April, early May. We are in Pátzcuaro, Michoacán, México, at an altitude of about 7,200 feet. May is the dry, warmest month of the year (before the cooler rainy season begins), with daytime temperatures in the low 80s. Several locals we asked call them “cumbos” but that doesn’t translate into anything that makes sense.
I’d like to have them identified so I could research their behavior, life cycle and possible control mechanisms. Hand removing them by flashlight is taking about an hour every night and getting tedious.
I took the accompanying photos last night. They very much alive, though perhaps a bit dazed from being unceremoniously interrupted in the middle of their favorite activities — eating and mating.
Thanks for any help you can provide.
Signature: Mark B Emmer
These are Scarab Beetles in the family Scarabaeidae, and they are most likely May Beetles in the subfamily Melolonthinae, but we are unable to provide you with anything more specific at this time. Perhaps a coleopterist, an entomologist who specializes in beetles, will write in and provide us with a genus or species identification. Meanwhile, you can read more about the subfamily on BugGuide.
Wow! Thank you. From the photographs on that page, it appears that Phyllophaga rubiginosa is a dead ringer for what we have. I’ll look closer at ours with a 10 power loope now that I have something to compare it to.
The links I found say the source is grubs in our lawn. I will go have a look now that I have some information on their life cycle.
Again, thank you for your help.
Pátzcuaro, Michoacán, México