Beetles and Parental Care

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.

(Schuster & Schuster, 1985)

Squeaky Beetles

Bess beetle (Passalidae) on decaying wood.

My labmate Paul brought me a box of bess beetles (family Passalidae) left over from a live insect lab.  I love these little squeakers, so I was pretty pleased.  I am not the only one who thinks the beetles are adorable.  BugGuide attributes the common name “bess beetle” to the French word baiser, “to kiss,” apparently due to the squeaky “kiss” noise these beetles make when disturbed.  This stridulation is produced by rubbing the top of the abdomen against the hind wings.  In fact, bess beetles produce at least fourteen distinct acoustic signals (Schuster 1983), giving them a pretty complex repertoire for an insect.

Less cute story:  when I was a kid, my brothers and I caught one of these for somebody’s science class.  We put it in a jar with some acetone and had to take it out again because it sounded like it was screaming.  (Anybody seen the Fly?)  Now that I’ve shared that adorable story, let me go back to talking about my awesome new pets.

Bess beetle chewing dead wood.

Bess beetles employ a fairly elaborate vocabulary because these beetles are subsocial.  Adults excavate galleries in the dark recesses of rotting wood where they live together in family groups, cooperatively caring for their brood.  Larvae are fed pre-chewed wood by the adults.

There’s an extra twist.  Unlike termites, bess beetles don’t have endosymbionts in their guts to digest wood for them.  Instead, they process the wood and excrete it, wait for microflora to further digest the wood, and then eat it again.  (Rabbits, as ruminants, employ a similar “eat it twice” tactic.  If I have destroyed your image of bunnies, I apologize.)  Both adults and larvae starve if they are not allowed feces as part of their diet.  Yum yum!