The approach of Halloween may bring to mind bats, crows, toads and spiders, but there is another creature that fits in with the holiday’s theme: the burying beetle, aka sexton beetle (Nicrophorus defodiens). It’s aptly named, as a sexton is a person who maintains a church’s buildings and churchyard, and whose duties once included digging graves. The adult beetles are strikingly and Halloween-ishly colored, shiny black with large splotches of orange or red. They have distinctive clubbed antennae that help them detect the scent of dead small vertebrates such as rodents and birds. Several weeks ago, I found a dead shrew in the garden with a beautiful burying beetle actively working on it. So why do these beetles want to locate little corpses?
Burying beetles will seek out a small, recently deceased vertebrate, such as the aforementioned shrew, and bury it by digging a hole underneath it, so that the carcass appears to be slowing sinking into the ground. The next step in this undertaking is to clean and process the shrew. The beetles remove the shrew’s fur and then apply their own secretions (let’s call them beetlejuices) to the carcass. These beetlejuices include antimicrobial substances that inhibit bacterial and fungal growth, helping to preserve the carcass until the beetles’ eggs hatch. The larvae and their parents then consume the shrew, with the larvae also begging food from the adult beetles. The parents regurgitate semi-liquid shrew, which is thought to be more nutritious than plain shrew and help the larvae to grow faster. Going from egg to adult takes several weeks and both parents protect the larvae until they pupate.
The period between the shrew’s death and the arrival of scavengers is critical because the first to arrive often get to consume the whole animal. It is most often a competition between flies that immediately lay eggs on the corpse (and then leave) and burying beetles who must undertake to bury, clean and preserve the shrew before laying eggs (and then stay with the corpse). If flies get there first and riddle the dead with their eggs, the maggots will get to consume the carcass at the expense of the burying beetles.
There is another challenge for the burying beetles. The adult beetles are usually infested with “large” Poecilochirus mites that are phoretic, meaning they catch a ride on the beetles, treating them like flying transportation or perhaps a Volkswagen, er, Beetle. These mites aren’t parasitic on the beetles but merely use them for rides from corpse to corpse. Upon arrival at their destination, the mites immediately disembark the beetle and disperse into the shrew’s fur. Poecilochirus mites are a mixed bag for the burying beetle. They sometimes cover the adult beetle’s body, interfering with walking and flying, and they also feed on the carcasses, directly competing with the beetle for food. But the mites also eat fly eggs, which reduces maggot competition for both the adult and larval burying beetles. The beetle-mite relationship, though fraught, seems to be stable: When scientists paired different species of burying beetle with the “wrong” species of Poecilochirus mite in a lab environment, both beetle and mite suffered.
With their conspicuous coloring, large size and awkward flight, burying beetles are easy to catch. However, you probably shouldn’t try, unless you are close to soap and water. Or unless you are planning to be a zombie for Halloween. Even from a distance, burying beetles smell rank and that rank smell will transfer to your hands.
Pete Haggard (he/him) and Jane Monroe (she/her) are the coauthors of Rewilding: Native Gardening for the Pacific Northwest and North Coast, available now from The Press at Cal Poly Humboldt and in local bookstores and nurseries.
This article appears in Red-Light Women, Part II.