Roundneck Sexton Beetle

Naming

Nicrophorus orbicollis Say 1825

Distribution

''Nicrophorus orbicollis'' adults are active in the early spring with the first adult beetles emerging in late May. Reproduction occurs from June to August and teneral adults appear from late July to early August. This species spends the winter as an adult and is found mainly in open and forested habitats.

Adults of the species are nocturnal. ''N. orbicollis'' is multivoltine with adults that care for their offspring during larval development. ''N. orbicollis'' is distributed from southeastern Canada to the southern tip of Florida and to East Texas; it has also been discovered as far west as Nebraska and as far north as North Dakota. ''N. orbicollis'' is the most frequently collected silphid species in the eastern United States.

Adults can be collected from February to October but are most commonly found during the summer months from June to August as a result of their efficient activity in warm weather. Most ''N. orbicollis'' have been collected in mesic forest habitats on human and carnivore feces as well as on rotten fruit and carrion.

Behavior

''Nicrophorus orbicollis'' males will search for small bodies of animals such as chipmunks, rabbits, and toads in which to attract a mate. Once a body is located the male will proceed to climb onto the carcass and emit a pheromone to attract a mate.

If another male enters the area, the two males will fight to the death and the winner will claim the carcass. Some males have been known to try to attract a mate without providing a carcass. These males will simply emit the pheromones even when they have not located a body.

If females are attracted they will mate, but then continue to search for a mate that does have a carcass. Females are more likely to lay eggs fertilized by the most recent mate, so the males that have a carcass are more likely to actually pass on their genes. Once a male attracts a female, the pair will proceed to bury the animal carcass together, equally sharing the workload.

If the carcass is too big for one pair, then it is acceptable for multiple pairs to work together to bury the carcass. Eggs are laid and buried very close to the carcass to provide a nearby source of nourishment. Unlike most beetle species, ''N. orbicollis'' parents will provide both food and protection for the larvae until pupation. It has also been observed that if one parent is killed the other parent will double up on the feeding and protection duties so the larvae do not suffer.

Without parental care the larvae cannot usually survive until the point of pupation.''Nicrophorus orbicollis'' is an endopterygote with complete metamorphosis; the life cycle consists of an egg, larval, pupal, and adult stage. Male and female beetles are attracted to carrion for reproduction and feeding. Male ''N. orbicollis'' attract females by emitting pheromones but they will only do so when a carcass is present. After mating, the female will lay her eggs from about 12–48 hours after discovering a suitable carcass.

Eggs hatch around 56 hours after oviposition. Once larvae complete development they pupate in the soil in 6–8 days. The size of a carcass affects the time span an egg is laid to when the larvae disperse and so also affects the time frame the parent beetles spend taking care of their young. In general, the time spent from egg burial to larval dispersal is less on smaller carcasses. ''N. orbicollis'' males will also spend less time taking care of their offspring when on small carcasses.

Larvae of most silphid species are dependent upon parental feeding but can sometimes feed directly from a carcass. ''N. orbicollis'' larvae, however, are extremely dependent upon their parents for feeding and will die before they develop to the second instar without parental care. Offspring mass is positively correlated with longer maternal care. ''N. orbicollis'' is nocturnal and must compete with dipterous larvae for oviposition locations on carcasses.

Reproduction

Larval ''N.orbicollis'' differ from other Silphidae by widely separated labial palpi. They also contain ten abdominal segments with the sternum separated into sclerotized sternal units called sternites.

''Nicrophorus orbicollis'' depends on small vertebrate carcasses to supply their young with an adequate food requirement. ''N. orbicollis'' mates mid-June to early August and is mostly active after sunset. First, the male attracts the female by producing pheromones.

Competition occurs between other burying beetles and other carrion competitors to secure a carcass for mating. It is commonly seen that N. orbicollis will compete with N. defodiens. The larger in size the beetle, the more likely it is to outcompete smaller beetles in acquiring a carcass.

Once the carcass has been secured and buried, the female lays her eggs in the soil surrounding the carcass. The larvae typically hatch 5–7 days later. Both the female and male have important roles as their larvae mature. Preservation of the carcass, protecting the larvae from predators and feeding the larvae are all roles taken on by the adults. The males then disperse from the carcass once the larvae have reached the final instar. The females will stay until the larvae disperse into the soil to pupate, usually 17 days after carcass burial.

Depending on the size of the carcass, the parents can control the number of offspring through a process called filial cannibalism. The parents do this to allow more space on a smaller carcass.

Burying beetles Nicrophorus orbicollis (Coleoptera: Silphidae) secure and bury small vertebrate carcasses as a food resource for their offspring and themselves. Burial may take place at the point of carcass discovery or at some distance from that site. Burying beetles were tested to determine if they discriminate between different substrates when burying a carcass.

Three substrates were presented simultaneously. Substrate one contained soil from typical beetle habitat; substrates two and three contained 2:1 and 5:1 ratios, respectively, of soil and a senescent prairie grass (Panicum virgatum), which added a bulk structural component to the soil. Beetles generally moved and buried the carcass within 24 hours. Results for both paired and individual trials suggest that burying beetles discriminate between substrates, preferring substrates with added bulk over those without.

Uses

''Nicrophorus orbicollis'' have not been found to have a direct effect on the economy. This species does, however, play a very important role in recycling. These beetles take a decomposing carcass and turn it into nutrients for their larvae. They do this by burying a carcass and feeding it to their young by regurgitation. These beetles secrete an antibiotic to delay decomposition in order to keep the competition away from the carcass so they will be able to feed their young.

There is little known about the medical importance of ''N. orbicollis''. Their ability to recycle dead, decomposing matter plays an indirect role in the health of the areas it inhabits. Natural antibiotics secreted by this beetle could potentially be medically beneficial in the future but currently nothing is known about the method of secretion.