Recovering a Strange, Elusive Gravedigger

by Hayley Dikeman

The American burying beetle (Nicrophorus americanus) is a large, vividly marked insect named for its practice of burying its food – carrion – for later consumption. Sometimes referred to as "nature’s gravedigger," this oddly colorful scavenger is a natural recycler, ridding the surface of dead animals and returning them to the food web.

Historically, American burying beetles were found over most of eastern North America, including 35 states and a portion of Canada. Since the turn of the century, the species has disappeared from over 90 percent of its former range. By the late 1980s, it was known only from two locations in two states—Latimer County, Oklahoma, and Block Island, Rhode Island. In 1989, the Fish and Wildlife Service listed the American burying beetle as endangered. Although the species is still at risk, populations are now known from 55 counties in eight states. In addition, there are three captive populations, two in zoos (Saint Louis Zoo in Missouri and Roger Williams Park Zoo in Providence, Rhode Island) and one at the University of Ohio.

Biologists often refer to the American burying beetle by the nickname ABB. The prevailing theory for the decline of this species is the loss, degradation, or fragmentation of its habitat. Land use changes result in increased competition from other scavengers, such as raccoons and foxes, for carcasses of the size beetles can bury. The numbers of these vertebrate scavengers formerly were controlled by higher predators, such as wolves and large cats. Developed areas also tend to create different assemblages of carrion species, which may be fewer in number and composed of carcass sizes not favored by the ABB. It has even been suggested that the passenger pigeon (Ectopistes migratorius), which once numbered in the billions, was an important food source for the beetle until this bird became extinct in the early 20th century. Lastly, the increase in artificial light can disrupt populations of nocturnal insects such as the ABB, reducing habitat suitability.

Feeding and Breeding

American burying beetles feed and breed on a variety of dead animals. Because carrion is a scarce and ephemeral resource in nature, the beetles must traverse large areas in search of it, aided by antennae that contain chemoreceptors (chemical sensors). By necessity, the beetles are strong fliers capable of covering substantial distances overnight. One-day movements of marked ABBs have been recorded at up to 3.72 miles (5.99 kilometers). On average, though, they move 0.8 miles (1.29 km) per day. Carrion selected by the ABB tends to be larger than that used by other burying beetles. Preferred sources are dead birds and mammals with an optimum weight of 3.5 to 7 ounces (99 to 198 grams).

For reproduction, a pair or group of ABBs will congregate on an appropriately sized carcass. Once the dominant pair is determined, it may move the carrion laterally for up to 3 feet (0.9 meter) before burial. So, how does a pair of insects bury such a large carcass? The beetles crawl under the carcass and dig the soil out from under it, slowly lowering the carrion into the soil. Then the ABBs cover the carcass with the excavated soil and create a chamber around it for rearing their brood.

The ABBs remove fur or feathers from the animal and secrete preservatives that retard bacterial and fungal growth. The female then lays eggs on or near the carcass. In a few days, a brood of three to 31 individuals hatch. Both parents typically remain with the carcass and larvae, feeding their offspring with regurgitated meat until the larvae are capable of feeding themselves. Eventually, the larvae burrow a short distance from the now-diminished carcass to pupate. New adults emerge from pupation within 30 to 45 days. Generally, the ABB produces only one brood per year, and these newly hatched adults overwinter to reproduce the following year.

Captive Conservation, Research, and Outreach

Because the American burying beetle is so rare and difficult to find in the wild, many recovery efforts have focused on learning about what conditions the beetle prefers and on growing populations in captivity for reintroduction into the wild. The Roger Williams Park and Saint Louis zoos have established the "recipe for beetle love," as the Saint Louis Zoo refers to the successful captive propagation of beetles. Zoo keepers fill a bucket with dirt and place a dead quail or rat on top, then put a male and female beetle in the bucket and let nature take its course. Once the next generation emerges, they are placed in a clear plastic box. Twice a week, they receive mealworms and wax worms to eat.

Since 1995, the Roger Williams Park Zoo has reared multiple generations of beetles and, working with the Service, has released over 1,000 pairs on the island of Nantucket, Massachusetts. In addition, the zoo has developed educational programs to spread the important message that conservation should not discriminate, and that all creatures deserve respect. The Roger Williams Park Zoo has been featured on the Discovery Channel, the children’s show "Arthur," and the syndicated show "Wild Moments," as well as in such publications as Wildlife Conservation magazine. More information about the zoo’s work with the beetle can be found at http://www.rwpzoo.org/conservation/beetlerecovery.cfm.

The ABB is the first terrestrial insect with an Association of Zoos and Aquariums-sponsored Species Survival Plan. This is a significant achievement. Louis Perrotti of the Roger Williams Park Zoo, in cooperation with the Service and other zoos and experts, developed this plan to maximize the beetle’s breeding success. To track individual beetles, each adult is given an identification number and its parentage is recorded. This ensures that each beetle does not breed with another beetle closer than a second cousin. Zoo keepers guide beetle breeding with a complicated formula based on each beetle’s age and genetic factors.

The Saint Louis Zoo has developed a Center for Conservation of the American Burying Beetle. The zoo has produced more than 1,000 ABBs, contributed stock for reintroduction into the wild in Ohio, and conducted surveys to determine if this species survives in the wild in Missouri. (Unfortunately, their surveys so far have not resulted in locating any wild ABBs.)

George Keeney with Ohio State University, in cooperation with the Service, maintains a captive breeding colony for release of beetles within the state. (See the following story.)

Conservation in the Wild

In Oklahoma, research into the ABB’s preferred reproductive microhabitat, specifically soil parameters, is being conducted by Dr. Amy Smith and Dr. Craig Clifford of Northeastern State University, in conjunction with Camp Gruber National Guard Training Center and the Service’s Oklahoma Ecological Services Field Office. In coordination with this research, the Oklahoma Department of Wildlife Conservation is working with Northeastern State University to expand this study. The Oklahoma Department of Wildlife Conservation has awarded Endangered Species Act section 6 funds to expand the microhabitat research to the Cherokee Wildlife Management Area, which is adjacent to Camp Gruber National Guard Training Center. This provides a large research area allowing for a large sample size. Preliminary findings should be available soon.

In Nebraska, Dr. Wyatt Hoback, with the University of Nebraska, is conducting multiple research projects regarding the ABB and other Nicrophorus species, including the effects of eastern red cedar encroachment, artificial lighting, and water loss.

Other agencies, such as the Federal Highway Commission and the Oklahoma Department of Transportation, are working with the Service to conserve ABB habitat and reduce impacts from transportation projects. The Ozark and Ouachita National Forests each developed a conservation plan with the goal of maintaining and increasing ABB populations on their respective forests.

The knowledge gleaned from better understanding this unusual creature can be applied to conserving additional invertebrates that provide nutrient recycling, pollination, and other important ecosystem services.

Hayley Dikeman, a fish and wildlife biologist in the Service’s Oklahoma Ecological Services Field Office, can be reached at hayley_dikeman@fws.gov or 918-382-4519.