American Burying Beetle

The American burying beetle (Nicrophorus americanus)—which belongs to the Phylum Arthropoda, Class Insecta, Order Coleoptera, and Family Silphidae—is a carnivorous beetle that feeds on and requires carrion to breed. It is the largest North American carrion beetle. In July 1989, it was placed on to the federal Endangered Species List; the International Union for Conservation of Nature (IUCN) currently lists the species as critically endangered. However, the U.S. Fish and Wildlife Service has proposed to downlist N. americanus from endangered to threatened under the Endangered Species Act. In the few states in which it is found, including Arkansas, it is ranked S1 (critically imperiled) by NatureServe. The decline of N. americanus has been attributed to habitat loss, alteration, and degradation, and they now occur over less than ten percent of their historic range. One author stated that this species’ case “must represent one of the most disastrous declines of an insect’s range ever to be recorded.”

The American burying beetle is between 25 to 45 mm (0.98 to 1.8 in.) long and is easily identified by its striking, distinctive coloration. The body is mostly glossy black, and on its wing coverings (elytra) are four scalloped, orange-red markings. Most notably, there is an orange-red marking on the large shield-like area just behind the head, the pronotum. This beetle also has orange facial markings and orange tips on its large antennae. The males have a large rectangular area of red marking on their clypeus (facial wall), while the females have a reduced, triangular red marking. The age of adults is determined by the intensity of appearance in coloration. After emerging from pupation, usually in spring or summer, young beetles are brighter and appear more uniform in color, while their exoskeleton is softer and in general more translucent. The pronotum of an early-summer, mature adult tends to be darker than the markings on its elytra, with the former appearing dark orange to red and the latter appearing orange. Mature, post-breeding (senescent) beetles have pale elytral markings and appear to be more scarred. They often have pieces missing from the margin of the pronotum or elytra, have defects in the exoskeleton, and/or are missing important appendages such as antennae, legs, or tarsi.

Historically, previous records reveal that N. americanus once occurred in at least 150 counties in thirty-five to thirty-seven states of the United States; in the District of Columbia; and in the Canadian provinces of Nova Scotia, Ontario, and Quebec. The historical range of this species included Alabama, Arkansas, Connecticut, Delaware, the District of Columbia, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, and Wisconsin. Collection records indicate that, east of the Appalachians, the American burying beetle declined in a generally north-to-south direction, and the decline was well underway, if not complete, by 1923. The decline occurred later west of the Appalachians. In the Midwest, the decline appears to have proceeded generally from the center of the range outward, with all collections since 1960 occurring at the peripheries of the range.

As of 2020, however, natural populations are known to occur in only six states and at least one Canadian province as follows: western Arkansas, southeastern Kansas, central and south-central Nebraska, eastern Oklahoma, Rhode Island (Block Island only), south-central South Dakota, and Ontario. South-central Nebraska has one of the largest metapopulations of N. americanus remaining in North America. Attempts to reintroduce N. americanus into Ohio and Massachusetts from a laboratory colony at Boston University are ongoing, and preliminary data suggests they will be successful in re-establishing them.

It is unknown why N. americanus has declined or outright disappeared from so many states. There are perhaps fewer than 1,000 individuals in the only remaining population east of the Mississippi River, and the Arkansas and Oklahoma populations (currently under study) are of uncertain size. The cause for the decline of the species is complex and difficult to discern. However, in order to implement an effective recovery program and to locate additional populations, it is necessary to understand the possible factors influencing the decline. It is suspected that widespread use of pesticides may have caused local populations to disappear, although the dramatic disappearance of this beetle from many areas took place before the widespread use of DDT. In addition, changes in land use have reduced the quantity of carrion of small to medium-sized birds and mammals used by N. americanus for reproduction. However, the prevailing theory explaining the disappearance of the American burying beetle involves habitat fragmentation. Fragmentation of large stretches of natural habitat changed the species composition and lowered the reproductive success of prey species required by N. americanus for optimum reproduction. Most importantly, not only do fragmented habitats support fewer or lower densities of indigenous species that historically may have supported burying beetle populations, but there is also now a great deal more competition for those limited resources among the “new” predator/scavenge communities.

The primary ecology of adult beetles includes a nocturnal lifestyle that includes searching widely as a strong flier for carrion. This particular beetle is remarkably proficient at detecting the odor of recently dead prey. Using the sense organs of olfaction located on their antennae, they can find a dead rodent (typical specimens weigh 100–200 grams) within one hour of death and from as far away as 3.2 km (2 mi.). After flying to the vicinity of a carcass, they drop to the ground and burrow through the litter to get to it. A male/female pair may move the remains several meters until a substrate soft enough for burial is found. They tunnel under the body, turn over onto their backs, and lift the carcass. However, no one really knows how a pair of beetles can “agree” on a burial site or how they are able to keep the carcass moving uniformly in one direction. They loosen the soil at the burial site by “plowing” through it. As the soil is moved upward and comes apart, and its roots are chewed through, soil from beneath the carcass is displaced to the side, and the carcass settles into the ground and is buried under several centimeters of soil. After burial, the beetles work the mass into a compact ball by stripping away its fur or feathers. Beetles will then “inoculate” the carcass with secretions that preserve the carrion and modify the course of decomposition.

Historical records offer little insight into what type of habitat was preferred by N. americanus. Current information suggests that this species was and still is a habitat generalist, with a slight preference for grasslands and open understory oak-hickory (Quercus–Carya) forests. However, as carrion specialists, they require carrion about the size of a medium-sized bird like a dove or a medium-sized rodent like a chipmunk in order to reproduce. Indeed, carrion availability is more important than the type of vegetation or soil structure and might be the greatest factor in determining where the species can survive. In the twenty-first century, N. americanus appears to be largely restricted to areas most undisturbed by human influence. In Arkansas, for example, work at Fort Chaffee Maneuver Training Center in Sebastian County indicated that this beetle is strongly associated with oak woodlands and native prairies, which are both priorities for habitat conservation and restoration in the state.

In terms of conservation efforts, the immediate goal is to reduce the threat of extinction of N. americanus by creating captive and wild populations. As part of this ongoing research, and in an attempt to establish another beetle population, biologists have released laboratory-raised N. americanus on historical habitats of the insect, such as Penikese and Nantucket islands in Massachusetts. Scientists return each year to both islands to study the survival and growth of this beetle population.

The life history of this insect is unusual in that it is one of the few species of coleopteran to exhibit parental care. Both the male and female take part in raising the young. Following winter, when temperatures are above 15°C (60°F), beetles emerge from the soil and begin reproductive activities. Males often initially locate carcasses and then attract a mate. Individuals usually fight over the carcass, often with the largest males and females winning. The victors then bury the carcass, the pair mates, and the female constructs a short chamber in an adjacent tunnel for egg deposition. Brood size usually averages twelve to fifteen, but ranges from one to thirty young. Returning to the carcass, the female prepares a conical depression on top of it. Both parents regurgitate droplets of partly digested food into the depression. The fluid accumulates as food for the larvae that hatch in a few days. Following egg hatching, the larvae develop, and both parents feed and tend to their young by regurgitating more food to begging larvae. The larvae grow rapidly and are soon able to feed themselves. The adults continually tend the carcass, removing fungi and covering the carrion ball with an antibacterial secretion. Sometimes the size of the brood is too large to be successfully reared on a small carcass, and both adults have been known to cannibalize their own small larvae. The larvae spend about one week feeding off the carcass then bury themselves in nearby soil to pupate and emerge as mature adults forty-five to sixty days after their parents initially bury the carcass. Beetles overwinter in the adult stage, and their life span is about one year.

The ecologically important task of carrion beetles and a vast host of scavengers like N. americanus is to recycle carcasses, ultimately returning valuable nutrients and recycling decaying materials back into the ecosystem. In addition, this beetle could serve as an “indicator species,” or one that reveals whether its environment is healthy. Understanding why its populations have decreased so drastically could provide indications of potential problems with both its habitat and the environment.

When the genetics of five N. americanus populations—collected from Arkansas, Nebraska, Oklahoma, Rhode Island, and South Dakota—were examined, results indicated that there were no diagnostic alleles for any of these five populations. This suggests that reintroduction of the American burying beetle to any state from another locality would probably not threaten the genetic makeup of any undiscovered local populations.

Although N. americanus forages widely and can be found in a variety of habitats, viable populations in Arkansas and Oklahoma could be limited to sites having deep, loose soils and surface litter, particularly mature forests. The habitat in these regions includes oak-pine and oak-hickory woodlands, open fields and grasslands, and transition zones. In one study testing this hypothesis, breeding pairs of beetles placed in a forest were more successful in burying prey and produced more offspring than pairs placed in a grassland. Recent collections in Arkansas and Oklahoma have generally been from level areas with relatively loose, well-drained soils, and a well-formed litter layer of previous years’ vegetation.

In Arkansas, N. americanus was rediscovered in 1992. It is considered the only endangered insect in the state. This beetle occurs in west-central and south-central Arkansas in eight counties: Clark, Crawford, Franklin, Johnson, Logan, Scott, Sebastian, and Yell. Two Arkansas Natural Heritage Commission sites that are part of the Arkansas System of Natural Areas (both in Franklin County) support populations of N. americanus: Cherokee Prairie and H. E. Flanagan Prairie. Since September 1992, N. americanus has been captured on four ranger districts of the Ouachita National Forest in western Arkansas and eastern Oklahoma. Most of these collections were found in the Tiak Ranger District in McCurtain County in Oklahoma, and in the Cold Springs Ranger District in Logan and Scott counties in Arkansas.

For additional information:
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Lomolino, Mark V., and J. Curtis Creighton. “Habitat Selection, Breeding Success and Conservation of the Endangered American Burying Beetle (Nicrophorus americanus).” Biological Conservation 77 (1996): 235–241.

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Szalanski, A. L., Derek S. Sikes, R. Bischof, and M. Fritz. “Population Genetics and Phylogenetics of the Endangered American Burying Beetle, Nicrophorus americanus (Coleoptera: Silphidae).” Annals of the Entomological Society of America 93 (2000): 589‒594.

Thomas, Brett. “Bugging the Oil and Gas Industry: The American Burying Beetle in Oklahoma.” Oil and Gas, Natural Resources, and Energy Journal 1 (2015): 221–240.

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Chris T. McAllister
Eastern Oklahoma State College