The Necrophorus beetle, also known as the burying beetle or the sexton has a very strange job in nature.
When a small animals die, the smell attracts these black-and-orange beetles. After finding the carcass (most usually that of a small bird or a mouse), beetles fight amongst themselves (males fighting males, females fighting females) until the winning pair (usually the largest) remains.
If a beetle finds a carcass and has no partner, then it will wait for one. Single males do so by releasing a pheromone from the tip of their abdomens. Females can raise a brood alone, fertilizing her eggs using sperm stored from previous copulations. The carcass must be buried by the beetle(s) to get it out of the way of potential competitors, which are numerous.
The probable parent beetles begin their task. The male beetle lies on its back beneath the corpse and moves it to a certain burial site. Then with the help of the female, it digs a hole below the carcass into which the it slowly subsides. While doing so, and after removing all hair from the carcass, they cover the dead animal with antifungal and antibacterial oral and anal secretions. This slows decomposition and prevents the smell of the rotting flesh from anticipating intruders or competition.
The female lays eggs in the soil around the crypt. The larvae hatch after a few days and move into a pit in the carcass which the parents have created
When the eggs hatch, the grubs feed on meat from the scavenged body till they themselves hatch, grow and become adults. Although they are capable of feeding themselves, both parents feed the larvae in response to begging, by reguirgitating liquid food for the larvae to feed on. This speeds up the development of the larvae.
The burial process can take around 8 hours. Several pairs of beetles may cooperate to bury large carcasses and then raise their broods communally.
It is also thought the parent beetles can produce secretions from head glands that have anti-microbial activity, inhibiting the growth of bacteria and fungi on the vertebrate corpse.
At an early stage, the parents may seek to reduce their population by selectively killing. culling their young.
Why is this? This is so that the number of larvae is proportional or matches the size of the carcass so that sufficient food can go around. If there are too many young, then all require to be fed resulting in lesser food for each. They will be underfed and develop at a not-so-fast rate, reducing their chances of surviving to adulthood. If there are too few young, the resulting adult beetles will be large but the parents could have produced more of them. The most successful beetle parents will achieve a good balance between the size of offspring and the number produced. This unusual method of brood size regulation might be the result of the eggs being laid before the female has been able to gauge the size of the carcass and hence how many larvae it can provision.
When these larvae grow to become adult beetles, they go on to continue as nature’s undertakers!