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American Burying Beetle
Nicrophorus americanus
Family: Silphidae
Description: The American burying beetle is the largest member of its genus (Nicrophorus) with individuals ranging in size from 1-1.5 inches (2.5 - 3.5 centimeters) in length. The body of this beetle is shiny black with two orange-red markings on each elytron (hard outer coverings over wings). The pronotum (area between head and wings) is flattened at the margins with a raised central portion. A key feature used in distinguishing the American burying beetle from other burying beetles is the large orange-red marking on the raised portion of the pronotum, a feature not found on any other burying beetle in North America. The antennae are large, orange at the tip, and clubbed.
| Status: |
Federally Listed Endangered (July 13, 1989) Global Rank: G1 State Rank: S1 |
Distribution: Historically, the American burying beetle occurred across most of the eastern and central United States (35 states), as well as Ontario and Nova Scotia, Canada. It is estimated that the distribution of the American burying beetle has been reduced to 10% of its former range and 1% of its original occupied habitat. Extant populations are widely scattered and the status (population density) of many of these populations is uncertain.
At present, extant populations are known only from Arkansas, Kansas, Oklahoma, Nebraska, South Dakota, and Block Island off the coast of Rhode Island. In Arkansas, extant American burying beetle occurrences are limited to five counties in the western part of the state. Most of these occurrences are from federal lands, such as Fort Chaffee Military Reservation and the Ouachita National Forest. Historical occurrences are also known from four other Arkansas counties. However, American burying beetles have not been observed in those counties since those historical collections.
Habitat: Surveys conducted on Fort Chaffee Military Reservation have collected American burying beetles from open habitats (open oak-hickory forests, grasslands). On the Ouachita National Forest, individuals have been collected from mature oak-hickory forests and pine stands. Large numbers of American burying beetles have also been collected from tallgrass prairie sites in Franklin County. Some studies have suggested that the American burying beetles is a relative generalist when it comes to use of habitat for feeding, moving over large areas and through diverse habitats in search of carrion. However, recent evidence seems to indicate that American burying beetles, at least those in the small populations that remain, have some affinity with open grassland habitats.
Diet: Adults and larvae feed primarily on the tissue of vertebrate (mammals, birds) carcasses. Adults may also prey upon other insects.
Reproduction: The location of suitable carrion is critical for American burying beetle reproductive success. Research has indicated that American burying beetle fecundity is highly correlated with carcass weight. Optimal carcass weight ranges between 3-6 ounces (100-200 grams). Reproductive activities take place at night, generally between April and August. Adult American burying beetles may move an average of 1 mile/night (1.23 kilometers/night) in search of carrion.
Once a suitable carcass is located, adult males may broadcast pheromones to attract females. Male and female American burying beetles will compete for the carcass with the largest pair of adults generally winning out. The established pair will then bury the carcass, typically before morning. As the carcass is buried, a brood chamber will be formed that houses the carcass. In this brood chamber, the adults will remove all fur/feathers from the carcass, form the carcass into a ball, and cover it with anal and oral secretions to retard decay. The pair mates and the female deposits her eggs in an exit tunnel adjacent to the brood chamber. Average number of eggs laid ranges from 12-15. Both the male and female may stay with the eggs until they hatch a few days later.
Parental care of the developing larvae appears to be critical to their survival. Larvae will remain in the tunnel for about a week, being fed regurgitated food by both the male and female parent. Larvae then move to the brood chamber to feed directly on the carcass. Eventually, the larvae pupate in the soil near the brood chamber and emerge as adults within 45-60 days. Emerging offspring will overwinter and breed the following year.
Conservation Status: The actual factors behind the decline of the American burying beetle are not well known. However, it is thought that habitat fragmentation and increased competition for suitable carrion resources may have played a significant role in this species initial decline. As their name implies, American burying beetles bury the carcasses of dead animals to rear offspring. As the largest member of their genus, American burying beetles tend to utilize larger carcasses than other burying beetle species, typically with an optimum weight between 3 to 6 ounces (100 to 200 grams). Smaller carcasses can be used, but can result in reduced reproductive success.
It has been suggested that fragmentation of large, continuous areas of natural habitat, that supported high densities of native species, lead to the reduction of appropriate-sized carrion resources for this species. For example, the loss of the Passenger Pigeon, once numbered in the billions and within the appropriate size range for the American burying beetle, might have had a concomitant effect upon this beetles decline.
Along with reducing native species within the optimum size range for American burying beetles, habitat fragmentation may have also lead to increased competition for limited carrion resources. As blocks of natural habitat are broken up, edge habitat is increased. Such habitat alterations can lead to increased densities of vertebrate scavengers such as raccoons, opossums, and crows, all of which compete for carrion resources. Other factors implicated in this species decline include spraying of pesticides and artificial lighting (parking lots, streets) which can reduce numbers of nocturnal insects.
Protection of areas containing extant populations is vital if this species is to survive. Along with protecting known populations, it is critical that surveys be conducted to locate additional remnant populations of this species. Captive populations of the American burying beetle have been established for the purposes of reintroduction into areas of historical occurrence. Reintroductions using captive bred stock have been conducted on two islands (Peniske and Nantucket) off the coast of Massachusetts with some success. American burying beetles have also been collected from populations at Fort Chaffee, Arkansas and released into suitable habitat in Ohio in an effort to reintroduce the species there.
