A bess beetle tends larvae in the interior of a rotting log (Photo courtesy Paul Lenhart).
A few weeks back I did a post on bess beetles, and their fascinating social structure. These beetles live together in family groups, communicate via an elaborate vocabulary of squeaks, and cooperatively care for the developing brood. Paul Lenhart recently snagged this awesome photo of an adult beetle with a group of larvae and was kind enough to let me share it with y’all here at 6legs. I thought I’d take the opportunity to do a bit more research and elaborate on what I learned last time.
Initially, a male or female beetle finds a rotting log, and begins hollowing out a tunnel. Later the beetle will accept a mate, following an elaborate courtship ritual complete with specific acoustical signals. The mated pair then cooperates on the tunnel and defends it fiercely from intruders. A clutch of about 30 eggs is laid in a nest of finely ground wood in the tunnel. When the eggs hatch into larvae, the parents cooperate to feed them specially prepared food–specifically wood which has been pre-chewed, passed as feces, and partially digested by microorganisms. When the larvae pupate, the adult beetles construct protective pupal cases around them out of wood debris and feces.
Interestingly, young adult beetles cooperate with the parents to help care for their siblings. The mated pair can have several clutches of eggs over the course of a year, and will often court and mate again in the nest when the initial brood has pupated. Newly eclosed young adults require several weeks or even months for their adult exoskeletons to fully harden and darken to black. These young adults are called “teneral” or “red” beetles, and remain in the tunnel, feeding larvae, helping to construct pupal cases, and defending against intruders. Evidence suggests they may sometimes remain even after reaching full adulthood, assisting their parents and siblings. Eventually, these beetles migrate from the log to join a mate and start their own family.
6legs2many 
Two things come to mind:
The larvae are much thinner than related scarab grubs, so they may not have the same amount of cellulouse-digesting bacterial flora and may operate on less bulk because of their preprocessed food.
The larvae must develop rather quickly if the parents are still around and reproducing when the kids reach adulthood. Lets wait a couple of million years to see the first social beetle hives evolve.
Good points!
Eusocial beetles actually do exist, although they’re not well known or well studied! The ambrosia beetle Austroplatypus incompertus lives deep in the heartwood of eucalyptus and has reproductive division of labor, overlapping generations, and cooperative brood care. One interesting factoid: The beetles apparently practice a sort of “foot-binding,” removing the tarsi of unfertilized female offspring, thus making them unable to move easily outside the gallery.
Loved your blog! I work with ants and had never heard of eusocial beetles! This is really good information! Deepest congrats! By the way, loved your post on the fire ants, I do the same flooding manoeuvre every month…
Thanks! I only heard of them because I found them in my colonies. Hands on learning! 🙂
WOW! That’s my beetle! I found one and was trying to get more info. Thanks. Please come check him out.
Can you see tracheal tubes in the larvae? They look like they might be pretty transparent.
I’m afraid I’ve only ever seen this picture. I could ask Paul?