Last fall, the future of the American burying beetle on Nantucket looked bleak.
“I thought we might have lost our population,” said Lou Perrotti, who has been working to preserve the beetle on the East Coast as the director of conservation programs at the Roger Williams Park Zoo in Providence.
Once found in a majority of states across the country, the endangered beetle, about the size of a wine cork, is found naturally in only one place east of the Mississippi: Block Island. In 1994, to try and create an insurance policy should a disaster fall upon the Block Island bugs, the zoo, the U.S. Fish and Wildlife Service and the Maria Mitchell Association worked to build a second population on Nantucket. That work is still ongoing, making it the longest-running introductory effort of an endangered invertebrate.
The Nantucket population steadily increased from 2004 until 2011, with help from conservationists. But after 2011, when the team looking after the beetles pulled back some of their help to see if the beetles could be self-sustaining, the population counts plummeted.
In 2011 there were an estimated 212 beetles on Nantucket. That was the population’s peak. Last fall, beetle trappings were in the single digits.
“We were scared,” said Perrotti, who has studied the beetles for 24 years.
But the beetles seem to be on the rebound. After the late summer collection, 93 beetles have been caught, according to Perrotti.
“I was shocked,” he said. The American burying beetle is a somewhat mysterious bug. It’s one of the rare insects in that both the male and the female take care of their larvae. To mate, the male and female find a dead animal, usually about the size of a rat, and bury it in the ground. The carcass, which can be anything from a bird to a bunny, is called a carrion.
The beetles go underground with the carrion and lay eggs in an adjacent tunnel. Once hatched, the whole family feasts on the carcass.
On Nantucket, scientists gave the beetles a head start by burying them with a “provisioned” quail carcass. As the population grew, experts started to rein in aid to the beetles to see if they could survive on their own. Once such provisions were scaled back in 2011, it was clear the beetles still needed a lifeline.
This spring, Perrotti and the Maria Mitchell Association created nine broods, giving them a bird and a hole about a foot deep and as wide as a dinner plate.
After their breeding period, the scientists planned to catch the beetles to try and estimate how many were left.
“We really didn’t expect to catch any,” said Emily Goldstein Murphy, the director of natural science at the association. But by June, they had caught 20. “I mean, to expect zero and get 20, that’s fantastic.”
Last year’s shockingly low numbers may have been because of the dry summer, Perrotti said, but it could also be because it’s hard to get an exact count of nocturnal insects that spend time underground.
“I know we are not getting every beetle. It’s a really hard thing to measure,” he said. “A lot of what we know about this species we learned in a lab.”
Some of these 93 beetles could have been ones that Perrotti and Murphy didn’t know about last year. They hope to get a clearer picture of the population breakdown.
That’s where Purdue University comes in.
The zoo has partnered with Purdue to help them figure out exactly what individual beetles eat. That information hopefully will separate which beetles are zoo-bred and provided with carcasses, and which ones are finding their own dead animals.
Brandon Quinby, a doctoral student at the university, can tell what the beetles have eaten by using a stable isotope analysis. By studying wing clippings from the beetles, he can find the ratio of nitrogen and carbon that will identify a food source.
“You are what you eat,” he said.
The beetles eat only birds or mammals that weigh between 80 and 120 grams. So Quinby has taken samples from animals that fit that bill on Nantucket. All of those animals have a signature nitrogen and carbon ratio and those signatures will show up within the beetles.
The analysis will not only allow scientists to learn the food preference of Nantucket beetles, but also reveal which beetles ate Perrotti’s quails and which have been eating others animals.
Quinby has used this technique previously with lab-reared beetle colonies from Oklahoma and Arkansas and it is commonly used outside of the insect world.
The swell in trappings this year and the future findings of Quinby’s analysis gives Perrotti hope to continue growing the Nantucket population. More broods will be introduced next year and provisions will continue under a five-year plan.
There is still much to be learned from the beetles, Quinby said, and the investment to saving the insects could have positive effects on the environmental and other benefits.
The carcasses that the beetles break down return nutrients into the soil, stimulating plant growth. The beetles’ secretions, which prevent their carrions from decaying and infection, are being studied for possible medical applications in wound care.
Understanding why the beetle numbers have decreased also may give officials indications to other problems with the environment, according to the U.S. Fish and Wildlife Service.
“We feel it’s worth putting the resources into the Nantucket population,” Perrotti said.