According to UNH professor of zoologyMichelle Scott, that stiff competition (please pardon
the pun) explains why burying beetles do what they do. Commonly found throughout the northern
hemisphere, these shiny black-and-orange insects are extremely sensitive to the odors of
decomposition, so they are often the first creatures on the scene after an animal dies. The beetles
can't defend their find from all of the competition, so they have to hide it--fast.
Typically, one male and one female beetle join forces to bury the animal, quickly excavating a
grave and maneuvering the carcass into it. If more than one beetle of the same sex turns up, there
is usually a fight, with the bigger beetle driving off the smaller one. Occasionally, a male and
female will allow additional beetles to help them bury a large carcass, like a chipmunk, which the
pair would not be able to handle alone.
A buried carcass is, in effect, the beetles' trust fund for the next generation. "Once the
carcass is buried about four inches below the surface, the beetles construct a brood chamber,"
Scott explains. "They mate as they're working on the chamber, and within two days the female lays
30 or more eggs in a side tunnel. Three or four days later, the eggs hatch and the larvae climb to
the top of the carcass, where both parents will regurgitate food to them."
The
larvae grow rapidly, increasing their weight tenfold each day, and are soon feeding on their own.
"When the young are three or four days old, one parent, usually the male, leaves," Scott says. "By
the time the young are eight or nine days old, they have polished off the carcass, leaving only the
largest bones. The larvae disperse to pupate in the soil, and the female's work is done."
This degree of parental care is quite unusual in the insect world. With the exception of social
insects like ants and bees, few invertebrates pay any attention to their young. Their general
policy is to produce as many young as possible and hope that some will survive. Why are burying
beetles different? It was to answer that question that Scott started studying them 17 years ago.
The key to the puzzle is that precious resource, the dead mouse. "Burying beetles are an
exception because they must find an unpredictable but very valuable resource in order to
reproduce," Scott says. "Probably an individual has only one or two chances to reproduce in a
lifetime, so each opportunity is tremendously important." A beetle's best bet for passing on its
genes, therefore, is to stick around and do everything it can to ensure the survival of the brood
it has already produced.