American Burying Beetle Nicrophorus americanus

This Bug’s for You
By Dave Thompson

This past April, Fossil Rim hosted a meeting of the Conservation Centers for Species Survival, of which it is one of five founder member institutions. Among the tasks undertaken by the participants of this meeting was a finalization of the species selected by the group for intense conservation efforts. Not surprisingly, the list contained larger animals like cheetahs, North African desert antelope and Attwater’s prairie chickens. Not all the animals discussed were of that scale. One of them was an insect. While not immediately engendering the charismatic appeal of the big guys, if you are fascinated by interesting life styles, this bug’s for you.

The American burying beetle, Nicrophorus americanus, is about 1.5 inches long and has a black, shiny carapace with bright orange markings on its back, wing coverts and head. Strong pincers equip the beetles as fierce fighters among their own kind and allow them to rip flesh into manageable pieces.

Incredibly sensitive antennae can pick up the scent of a mouse or quail within as little as an hour after it has died and from as far away as two miles. Once the beetle has detected the scent of the fresh carrion, it must get to it in all haste to avoid such possibilities as another scavenger taking the carcass, or of it being spoiled by flies laying their eggs upon it. Several beetles may converge on the dead animal, and, in that case, the battle for the precious resource is on. Males fight only other males and females fight only females until just a pair, usually the largest combatants of each gender, are left.

The triumphant pair then must bury their prize. If the soil is soft enough where the carcass lies, they will bury it there. If a more suitable burial site is needed, the beetle pair crawls under the carcass, flip over on their backs and, in tandem, lift the carcass with their legs. It is believed that the beetles are able to thus judge the weight of their prize. Ideally, the carcass should be somewhere within the 2-7 ounce (50-200 grams) range. To move such dead weight, which far exceeds the combined weight of the beetle couple, for a considerable distance, as much a 100 yards away, requires some incredible team work. With the carcass still suspended by the beetle pairs’ powerful legs, they move it a fraction of an inch by using their legs as a miniature, short run conveyer belt. They repeat the process over and over again until they have reached their destination.

After arriving at a suitable burial spot, the beetle pair begin digging the soil out from under the carcass until it has settled completely below the ground. Working underground, the beetles next roll the carrion into a ball, and embalm it with secretions from their mouths and anuses that will help strip away fur or feathers and help “embalm” the carcass.

With the carrion in place and properly processed, the beetle pair will now mate and the female will lay up to 30 eggs in the soft soil mixed with the fur or feathers of the corpse. Ideally, the process of moving and burying the future food of the young beetles is carried out at night, when the temperatures are cooler and there are fewer flies about that might spoil the prize by laying their own eggs on the carcass. To aid in the care of the carcass, the beetles have an interesting relationship with tiny mites that live on their bodies. After the carcass is buried, the mites hop off the beetles’ bodies and eat whatever fly eggs may have been deposited on the carcass. The adult beetles continually tend the carcass, removing any fungus that might grow and by covering the carrion with a special antibacterial secretion.

Within a few days, the eggs hatch and the emerging larva begin to beg for food by tickling the parents’ jaws. The parents’ respond by ripping chunks of flesh from the embalmed carcass and feeding it to their young. This process will be repeated many times over the next week until the young have consumed the entire corpse, save for the bones. If the couple’s fecundity has the prospects of exceeding the projected food supply, the adults will consume a portion of the larva, sacrificing a few of their own young so that the majority will have enough food to survive. The surviving young then pupate for another month, after which they emerge from the combination tomb and nursery as fully developed adults. Their parents die soon after emerging form the underground chamber.

Although the American burying beetle is not the sole example of providing such devoted parental care to its young (think bees, wasps, termites and ants), the beetles are unique among all known insects in that they do this not as social insects, but as a lone couple.

The American burying beetle was once found throughout the United States, east of the Rockies, thirty-five states in all. They were also found in southern Ontario, Quebec, and Nova Scotia. Today, they naturally occur only on Block Island, off the coast of Rhode Island and in a few tiny isolated patches in the mid western states of Oklahoma, Arkansas, Kansas, Nebraska and South Dakota. No one is sure what caused the beetles’ population crash. Possibilities include habitat fragmentation, light pollution or the reduction of larger predators such as wolves, bears and pumas which allowed foxes, raccoons and skunks to become the primary predators within the range of the burying beetle. These smaller predators would choose and consume the same animals, some of which, otherwise dying of natural causes, would provide potential for sources of food items for the beetles’ young. An interesting speculation involves the demise of the passenger pigeon which once numbered in the billions and lived in the same region. That many birds produced a large number of young that did not survive the period from hatching to fledging. The dead squabs would have fallen within the ideal weight range of the carcasses preferred by the beetles.

The American Burying beetle is a rather unique part of the biodiversity of the Midwest. Unfortunately, it is almost gone. The species was listed as endangered in 1989. It is estimated that the total number of the species still surviving in the wild may be as low as two thousand. Why should the average person care? Altruisms of protecting all forms of life aside, we know very little about the antibiotics that the adult beetle secrete to protect carcasses for their young. For all we know at present, that substance might hold some promise in the efforts to provide an addition to the arsenal of the pharmaceuticals we are depending more and more on to preserve our own health standards.

A few AZA members are working on giving the American burying beetle a helping hand. The Roger Williams Park Zoo in Rhode Island has developed successful techniques to produce the beetles and has been releasing the progeny to the wild. Fossil Rim’s fellow C2S2 member, the Wilds near Cumberland, Ohio, has pledged resources to the same goals. Look for an American burying beetle initiative at Fossil Rim in the near future.