One of the world’s best insect undertakers is making a comeback.
Populations of the American burying beetle, North America’s largest carrion beetle, have been decimated due mainly to habitat loss and dwindling wildlife species. Once abundant in 35 states and three Canadian provinces, the American burying beetle is now found only in small pockets in 10 states.
But new data show that the beetle’s abundance increased over the last decade in southwestern Nebraska’s Loess Canyons. It’s the first regional increase since the insect was listed under the Endangered Species Act in 1989, researchers report in the January Biological Conservation.
“This is the holy grail of threatened and endangered species conservation,” says Caleb Roberts, a research ecologist with the U.S. Geological Survey’s Arkansas Cooperative Fish and Wildlife Research Unit in Fayetteville. “You don’t get many comeback stories with teeny species, especially at this scale.”
The increase in carcass-eating beetles in the Loess Canyons is a good sign for the prairie as a whole, Roberts says. The giant insects are indicators of how grassland ecosystems are faring.
American burying beetles (Nicrophorus americanus) clean up dead bodies. The five-centimeter-long beetles bury vertebrate carcasses. Then, the beetles embalm each carcass with secreted anal and oral fluids to feed themselves and their babies (SN: 10/15/18). While the insects aren’t picky about what kind of dead animal they eat — anything from a lizard to a rat to a bird will do — they are picky about its size. To successfully feed their larvae each summer, the beetles need a carcass that weighs 100 to 200 grams, about the size of a small rabbit.
But available bodies have been dwindling (SN: 12/22/23). For instance, now-extinct passenger pigeons were a perfectly sized prey for American burying beetles. Same with prairie dogs and bobwhites, which have disappeared from much of North America’s grasslands. The beetles also need moist soils not covered by dense leaf litter or vegetation for burrowing, which can be harder to find as America’s grasslands are plowed for crops or invaded by trees.
From 2007 to 2019, the Nebraska Game and Parks Commission sampled American burying beetle populations across the 130,000-hectare Loess Canyons landscape by baiting five-gallon buckets with dead laboratory rats. Analyzing that data, Roberts and colleagues found that the total beetle population across all traps during the study period increased by 17 percent, from 168 beetles to 196.
Next, the team modeled beetle population trends based on different types of land cover in the Loess Canyons. Models show that burying beetles strongly prefer Nebraska’s native grasslands free from eastern red cedar. If perennial grasses cover roughly three-quarters or more of the Loess Canyons, beetle populations are predicted to double, the new data show. However, once tree cover reaches more than about 10 trees per hectare or when just 0.1 percent of native grasslands are plowed for planted crops, beetle abundance plummets to nearly zero.
The reason behind this first upward trend in American burying beetles echoes what’s been documented in previous studies, says entomologist Wyatt Hoback of the Oklahoma State University in Stillwater.
More cedar trees invading historically tree-free prairies equal fewer burying beetles. Fire suppression efforts have allowed the fast-growing red cedar to outcompete native perennial grasses throughout the Great Plains, which displaces wildlife like these beetles (SN: 12/6/23). Nebraska, in particular, is losing about 2 percent of its grasslands each year to encroaching eastern red cedar trees, says Thomas Walker, a wildlife biologist with Nebraska Game and Parks Commission.
But beetles are booming in the Loess Canyons thanks to a coalition of more than 100 private landowners who reintroduced fire to restore their prairie pastures. In partnership with Nebraska Game and Parks, the U.S. Department of Agriculture’s Natural Resources Conservation Service, Pheasants Forever and others, landowners have burned more than a third of this vast landscape since 2002, reducing tree cover in some places back to historic levels of less than 10 percent.
Reintroducing fire and controlling eastern red cedar in the Loess Canyons has created more diverse prairie habitat, which supports more wildlife species. This, in turn, gives beetles more food options.
“It’s been very rewarding working with these landowners,” Walker says. “Ultimately, they’re the ones that are leading the success on all of this.”