KNOCK KNOCK, WHO'S THERE? DEATH

In England, in a time when people died at home, family members would remain at the side of their loved ones through the night.  In the silence, a tapping could be heard.  This was storied to be Death, tapping his fingers, waiting… In reality, it was a wood-eating beetle looking for love.

Southern England is the home of Xestobium rufovillosum, a small beetle that feeds on decaying wood.  During its life cycle, eggs are laid on wood (often with a fungi already present), the eggs hatch and the larva feeds on the wood.  The larva may remain, chomping away for up to 15 years, causing tremendous damage to furniture and homes.  The larva will then pupate and emerge as an adult.  The beetle is now ready to look for love.  The male will pound his head onto wood, making a knocking noise.  If a female is present, she will knock back.  They will continue this awkward form of “Marco Polo” until they meet.  Cue the romance sound track!

But wait!  Females are picky and will not settle for just any head banger.  First, she must size him up.  It turns out that females choose heavy males to mate with.  Presumably the heavier the male, the better.  The researchers who determined this applied blue tack (like you used to stick posters to your dorm walls) to males to make them artificially heavier and then presented them to the females.  Females consistently went with the heavier males, even if they were “skinny” blue, and tacky dudes.  Apparently, males donate an average of 13.5% of their body weight to females during mating (Goulson et al 1993).  What does this mean?  Well, that would be equal to a 200lb male human delivering 27lbs of sperm.  Clearly, the deathwatch females think more is better.  So now you know the rest of the story.  It wasn’t Death knocking at your door.  It was a wood-eating beetle looking for love in an old, decaying house.

Goulson D., M.C. Birch and T.D. Wyatt.  1993. Paternal investment in relation to size in the deathwatch beetle, Xestobium rufovillosum (Coleoptera: Anobiidae, and evidence for female selection for large mates.  Journal of Insect Behavior.

(Did anyone else think the name of the first author of the research paper was hilariously appropriate?)