The family Silphidae is home to a number of species that are all specialized, in one way or another, to utilize decaying animal carcasses for food and shelter. The genus Nicrophorus (burying or sexton beetles), for instance, is known for working quickly in pairs to excavate soil under small, dead animals and encase them in earth. This both prevents them from drying out and keeps competitor insects from laying eggs in the carcass that would compete with the carrion beetles’ own larvae. They are even known to have a symbiotic relationship with tiny mites they harbor on their bodies, which eat fly eggs that have already been laid in the carcass. Carrion beetles in other genera, such as Necrophila, however, avoid this complication by specializing on older, drier carcasses that rarely harbor fly larvae. There are many genera of carrion beetles, comprising about 46 species in North America. Many carrion beetles have incredibly specific callings—Nicrophorus tomentosus, for example, is found primarily on small dead animals suspended in the air; N. marginatus specializes on dead snakes; Silpha bituberosa (unusually) feeds on spinach, beets, and squash, among other vegetables.
Adult N. americana reproduce in late May through mid-July, laying their eggs on carrion of many varieties. Although both the adults and larvae have been observed to feed on decaying flesh near soft parts and excretions, the larvae seem to feed primarily on dried sinew, hide, and skin left behind after the dipterous larvae have vacated the carcass. Development from eggs to adults is completed in 10-12 weeks, and the first brood of larvae emerges as adults in late July or early August. These beetles overwinter in as adults and mate the following spring, such that only one generation of N. americana occurs every year. In addition to carrion, adults also feed on larvae of other species, further reducing the competition their own offspring face.
The adults are broad, distinctive beetles 13.8-20 mm in length. They have a yellow thorax typically marked with an irregular central black spot. In females, the apical tips of their black, rough elytra are usually brushed with yellow. It is thought that N. americana mimics Psithyrus ashtoni, a cuckoo bumblebee, as a defensive mechanism; the two are found in similar habitats at the edges of fields and forests. Fisher and Tuckerman (1986) wrote that “our attention was drawn to the similarities between females of Psithyrus ashtoni and adults of Necrophila americana during the spring of 1982, when one of us, while looking for Psithyrus females, mistakenly chased an adult N. americana.” The two have similar morphologies in flight, overlapping ranges, coinciding flight periods, extremely similar flight patterns. The authors note that this is one of many instances of apparent mimicry between carrion beetles and bumblebee species.
This larva was found in the grass behind the laundry; the adult male was found in the powercut across Rt. 613. Neither were apparently near any carrion.
- Fisher, Richard M, and Robert D Tuckerman. "Mimicry of Bumble Bees and Cuckoo Bumble Bees by Carrion Beetles (Coleoptera: Silphidae)." Journal of the Kansas Entomological Society 59.1 (1986): 20-25.
- Marshall, Stephen A. Insects: Their Natural History and Diversity. Firefly Books Ltd., 2006.
- White, Richard E. A Field Guide to the Beetles of North America. Boston: Houghton Mifflin Company, 1983. Peterson Field Guides.