Sexton or Burying Beetles

The undertakers of the insect world . . . . . .

Sexton or burying beetles belong to the family of beetles called Silphidae (Carrion Beetles). There are several species found in the British Isles, and apart from the black sexton beetle, Nicrophorus humator (top left), which is entirely black except for its red tipped antennae, all have distinctive red-orange markings on the wing-cases, as in the other example illustrated and appropriately called the banded sexton beetle, Nicrophorus investigator (bottom left).

Sexton Beetles are found on carrion and often bury small dead animals (rodents, birds, etc.) as a food store for themselves and their offspring. The beetles can fly long distances to locate carrion, presumably attracted by smell. When the beetles find a small carcass, they creep underneath and excavate the soil below, pushing it to the sides and using their jaws to cut away obstacles, such as grass roots. In this way the dead mouse or bird slowly sinks into the earth until it is completely buried. The female beetle lays her eggs in the soil, close to the buried carcass, and remains there until the eggs hatch. There appears to be some degree of parental care, in that the female beetle regurgitates a brown liquid of partly digested food for the young larvae, until they are large enough to eat the carrion on their own. The fully grown larvae burrow into the soil to pupate, away from the remains of the carcass (if any), and eventually emerge as new adult beetles to start the cycle over again. Thus, sexton beetles are beneficial as scavengers by helping to clear away the corpses of dead animals.

These beetles are frequently infested by tiny reddish-brown gamasid mites (Gamasus species), which cluster between the body segments, under the wing-cases and anywhere else that the beetle cannot easily reach with its legs to dislodge them (see below). The mites are thought to suck fluid from the beetles but this activity seems relatively harmless and many of them may be just 'hitching a ride' as the beetles fly off to new habitats in search of carrion. The same or similar mites are also associated with many of the large flying scarab or dung beetles and heavy infestations are often found on the young queens of some bumblebees.

Banded Sexton Beetle (Nicrophorus investigator) infested with gamasid mites
 
Photos: J. A. Weir ©