The Carlisle Mosquito Online

Friday, September 28, 2007


Burying beetle

This burying beetle was interrupted at Towle Field during its work on a dead starling. (Photo by Kay Fairweather)
Among nature's many niches is the protein-rich food source of an animal carcass. Crows, raccoons and turkey vultures are well-known as scavengers but insects, too, compete for carrion and help keep the neighborhood clean. Several species of flies and beetles have evolved to take advantage of this niche. Burying beetles have developed an unusual strategy to improve their chances of survival. This is their story.

Name. Burying beetles, also known as Sexton beetles, are members of the genus Nicrophorus. There are 15 species in North America and two of these were represented at the edge of the Towle Field parking lot on September 21 to 23. There were three beetles present: a pair of N. tomentosus and a solitary N. orbicollis.

Identification. Burying beetles are black with orange markings. The orbicollis was just over an inch long and the tomentosus just under. N. tomentosus is differentiated by the light-colored hairs on its thorax. Both species have club-shaped antennae. Burying beetles typically carry several round reddish-colored mites. Sometimes they have so many mites you can hardly see the beetle.

Some of you may not look very closely at the dead critters you come across. Those who do are more likely to see carrion beetles which don't have the orange bands on the wing covers. They are also wider, relative to their length, than the comparatively slender burying beetle.

Burying beetles can also be recognized by their behavior — they will be burying a rodent or a bird or scouting for such an item. A friend in Concord saw one flying around a garbage can that contained meat scraps. The ones at Towle Field were burying a starling, which is a bit like you or me trying to bury a school bus.

A pair of beetles buries a mouse (the furry blob at the right) in Kay Fairweather's back yard in 2001.The circle on the beetle at the top marks of the mites commonly found on burying beetles. (Photo by Kay Fairweather)
Competitive strategy. Burying beetles can't reproduce without first finding a small vertebrate carcass that their larvae will feed on. This is a prized resource which the beetles attempt to conceal from other carrion seekers by burying it. They use their legs to scrape the soil from under the carcass so it sinks into the ground and is less accessible to competitors. They typically work in pairs for speed (12 legs are better than six), but even so it is likely that flies will already have laid eggs in the carcass — so onto the next part of the strategy.

The mites that were hitching a ride to the carcass restaurant disembark and repay the favor by eating fly eggs. This reduces the fly larvae population and leaves more food for the beetle larvae. If the mite-fly balance is not right, the mites may also eat the beetle eggs. Adult burying beetles have yet another way, rare in the invertebrate world, to help ensure the health of their offspring. They stay around until their eggs hatch and tend to the young. They remove feathers or hair from the carcass and pre-chew pieces into nutritious snacks which they feed to the larvae.

This handsome Great Blue Heron was spied on Buttrick Pond. (Photo by Mollie McPhee Ho)

References. Kaufman Field Guide to Insects of North America, Eric R. Eaton & Kenn Kaufman; Insects, Their Natural History and Diversity, Stephen A. Marshall. Both books are fairly new. Kaufman is excellent for anyone looking for an all-purpose insect field guide. The Marshall book is a photographic guide with 4000 pictures of insects of eastern North America — a heavy book — not for the field.

Submissions for the Biodiversity Corner are encouraged from everyone. What are you finding? Send a note to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to

2007 The Carlisle Mosquito