Beautiful, Bizarre Burying Beetles Act as Nature’s Undertakers
I don’t often shake down my cat for a dead mouse, but I did think it was fair, considering that he is always shaking me down for his cat food. I wasn’t going to eat his mouse. I needed it as bait, to see if I could catch a burying beetle.
Burying beetles, or sexton beetles, are nocturnal, and they spend much of their lives underground. You’re most likely to find them under small dead animals, such as moles or mice, in a field, that is if you get there before the crows, raccoons, ants, worms or bacteria do.
I first encountered burying beetles in the mid-1980s, while working on a master’s thesis on Block Island, off the Rhode Island coast. This is where I also met Andrea Kozol, a Boston University student who was studying the giant, very rare American burying beetle (Nicrophorus americanus). We spent many an evening catching insects with low frequency light, and I would occasionally visit her trap lines.
Twenty-five years later, she’s a university professor and a world authority on the restoration and protection of the American burying beetle (still thriving on Block Island, thanks in part to her work) and I’m living in Vermont, stealing dead mice from my cat so I can catch some local specimens, and tell you why they’re so cool.
Burying beetles — there are some 19 species in the genus Nicrophorus — are one of nature’s most efficient undertakers. Some are generalists, while others are attracted specifically to the carcasses of particular animals, such snakes, birds, mammals and fish.
On a warm summer night, a pair of burying beetles might bury a recently expired bird or mouse 6 to 8 inches deep. This is no small feat. Most burying beetles are roughly ½ to 11/2 inches long. Think of a pair pygmies burying an elephant, and you get the idea of the scale involved.
How do they do it? Their physical adaptations include hyper-sensitive chemo-receptors on the ends of their antennae. They use these to find carrion, sometimes traveling miles on the scent trail at night. Once they find the right sized carcass, they use specialized structures on their legs to excavate a chamber. After the body is buried, they go to work coating it with chemical agents that work as anti-bacterials and fungicides. These retard decomposition. The beetles lay their eggs under the carcass, and when the eggs hatch, the meat provides a feast for their developing young.
Burying beetle parenting behavior is equally, well, parental. They hang around to feed and protect the developing larvae after the eggs hatch. The dead animal becomes a type of family bed. According to Kozol, this level of parental care is found in the social insect groups — ants and bees — but is highly unusual in beetles. The adults also manage pest control — they feed on fly larvae, and carry with them mites that have co-evolved to feed on fly eggs in the burial crypt.
In order to catch burying beetles, I dug a pitfall trap in the garden, and placed a Ball jar in it. Then I fashioned a rough roof out of sticks and a piece of cardboard to keep the rain out. I put the dead mouse in the bottom of the jar, and I went back into my house to wait.
It didn’t take long. In the morning I had a pair of burying beetles. Were they a breeding pair? Quite possibly. One was noticeably larger. (Mysteriously, the mouse was gone. I suspect the skunk that lives nearby.) My burying beetles had four telltale dabs of orange-red roughly in the shape of w’s on their backs. Under closer magnification, I could see that each beetle was carrying mites. The antennae were especially impressive up close: segmented like the rattle on a rattlesnake, and pointed — like NASA remote sensing arrays. The legs were, surprisingly, less paddled than I thought they’d be. They were much more refined, sculpted with long narrow hooks on the ends, feathery widened places below, bladed like sweeps on a dory. The legs looked like they had to leverage small rocks as well as move dirt: maybe that’s part of the job description, living on glacial till.
What’s the take home of taking a close look at burying beetles? For me it was the reminder that nature is both beautiful and bizarre.
Tim Traver is an author and freelance writer. Previously, he served as executive director of the Upper Valley Land Trust and co-directed the social service organization COVER Home Repair. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: firstname.lastname@example.org