This cemetery is swarming with 5.6 million bees

The soft ground of the dead in upstate New York is buzzing with swarms of the living—the largest group of ground-nesting bees ever recorded worldwide. 

“It’s a massive aggregation of bee nests,” says Bryan Danforth, an entomology professor at Cornell University.

These roughly 5.6 million bees—discovered recently in a cemetery in Ithaca—have expanded researchers’ knowledge of the types of habitats that native bees prefer. The discovery also reveals the pollinating engine that helps produce apples at Cornell University’s nearby apple orchard.

“These [old cemeteries] are really good sites for ground-nesting bees,” Danforth says. “The bees and the people like this soil for the same reasons.”

These bees, known as regular mining bees (Andrena regularis), typically emerge from their burrows to mate in the spring. But despite their large numbers, their nests have remained hidden from scientists’ awareness—until someone stumbled upon them.

Solving a 10-year pollinator mystery

Danforth has been surveying bees in New York state for years. About a decade ago, he worked on a team that found that regular mining bees were the third most common bee species in apple orchards across the state. But in Cornell’s apple orchard, they were more common than any other bee species. Just the same, Danforth never knew where so many mining bees came from.

Then, one day in the spring of 2022, Rachel Fordyce, a technician in Danforth’s entomology lab, found herself surrounded at the peak of a mining bee bacchanalia. She often parked her car for free across Cornell’s campus, cutting through a cemetery on her route to Danforth’s entomology lab.

At the cemetery, Fordyce saw males “pouncing on females” and females disappearing with cargo loads of pollen and nectar into their nest holes on the ground. She captured a few in a jar to bring to the lab. The team returned to see “a cloud of bees” in a “frenzy of activity,” Danforth describes.  “It’s fun to watch, it’s one of the coolest things to see.”

The East Lawn Cemetery was about half a mile from the apple orchard—not too far for a mining bee. “Rachel’s discovery kind of solved this mystery that had lingered in my mind for about 10 years,” Danforth says.

The team later walked the perimeter of the nesting site, noting that most of the nests were in an area measuring about 1.5 acres in total. They then waited for the next spring, when they could conduct a proper bee census at the site.

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Two giraffes worth of bees

While the bee nesting site is dense, this aggregation is more of single-home neighborhood than a packed hive like those of honeybees. Regular mining bees typically each dig their own holes for their eggs. “The females are very good diggers, they build with their mandibles and their legs,” Danforth says.

In a vertical shaft that goes down 6-10 inches, they dig out a side passage and create a brood cell—a small enclosed compartment lined with waterproof secretions. They place a ball of pollen and nectar inside and lay a single egg upon it before sealing the brood cell and backfilling the passage. They do this day after day, laying roughly 6-8 eggs in different side passages of the same vertical shaft before burying the whole thing. When a larva hatches, it eats the provisions for the following months, molting in several larval stages before transforming into a pupa. By the time the fall comes around, it will have reached adulthood, but it spends the winter sleeping off the effort in a hibernation-like state called diapause, where their metabolic rate goes way down.

Danforth isn’t sure exactly what wakes the bees from their underground slumber—he suspects it’s a kind of biological clock, though, since they all begin to emerge around the same time to mate when temperatures hit around 70 degrees Fahrenheit.

In 2023, the team was ready for the next generation of regular mining bees in the cemetery. They had placed little mesh tents at random places within the nesting site they’d marked off the year before. Each tent had a jar at the top filled with alcohol where the bees would collect. The team counted bees, identified their sex and noted any other species they found in their traps.

Using models in their study, published recently in the journal Apidologie, they estimated the population at around 5.6 million bees in this 1.5-acre area—almost four times the human population of Manhattan. Calculations revealed the biomass of all these mining bees would amount to nearly 10,000 pounds—the weight of two fully grown giraffes.

Danforth says these 5.6 million bees would amount to roughly 140-180 average sized honeybee colonies. “The numbers were pretty astounding,” Danforth says. “No sane beekeeper would put 140-180 honeybee colonies in a 1.5-acre field.”

Sam Droege, a wildlife biologist at the U.S. Geological Survey’s Native Bee Lab in Maryland who wasn’t involved in Danforth’s study, says he was surprised about the sheer number when he saw this study.  “That was crazy—it was bigger than I’d ever heard of,” he says. “It’s very unique because they actually quantified this.”

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Sealed with death

The Cornell entomologist team didn’t stop there—they found another layer of underground macabre activity sharing the same earth as human corpses. In their traps, scientists captured cuckoo bees (Nomada imbricata)—a parasitic species whose mothers take advantage of the hard work of the mining bees. They emerge a little after the mining bees in the spring, around the time the females are digging holes to lay eggs. A cuckoo bee female will then sneak in and lay its eggs in the brood cell of a mining bee, camouflaging it in the brood cell’s wall.

“Once the egg is laid, it’s like a ticking time bomb,” Danforth says. A heavily armored larva emerges from the cuckoo egg that quickly kills the mining bee and steals all the food, growing into an adult in the host’s brood cell.

Mining bees also face threats from blister beetles, a parasitic insect that lays its eggs in flowers, which hatch into mobile larvae. These larvae latch onto female mining bees, hitching a ride to their brood cells, where they kill the mining bee larvae. Besides those beetles, the team also observed conopid flies, which lay their eggs directly on mining bees; they hatch and burrow into the adults. “They are flying around dive-bombing adult females,” Danforth says.

None of these parasites damage the mining bee population on a broad scale. But the scientists’ clear documentation of these relationships between species is “unique,” Droege says, as entomologists don’t always have a good understanding of the relationship between bees and their parasites.

Based on the 5.6-million-bee discovery, Danforth has launched a state-wide survey of cemeteries in New York, and an iNaturalist project that harnesses the observations of citizen scientists to find more bee nesting sites. “I wouldn’t be at all surprised if there were larger aggregations out there,” he says. So far, he’s found the older graveyards are ideal for nesting sites since they were often placed in areas with sandy soil. This was important for easy digging, whether bee mother or gravediggers.

Cemeteries also don’t use a lot of pesticide compared to farms or even lawns, and the older ones tend to be more overgrown—which may be good for pollinators. “They are refuges from pesticide use, they have the right soil texture, they have pretty good floral diversity, they’re quiet and undisturbed,” Danforth says.

Droege says that cemeteries may not be the ideal type of habitat for bees overall, but amid an urban environment, they may still provide some value to pollinators. “There’s a whole series of people doing investigations of cemeteries because they’re filled with rare plants and maybe there are rare bees,” Droege says. Homeowners can take lessons from this finding, he says, to improve pollinator habitat in their yards by avoiding pesticides and swerving away from the picture-perfect, well-manicured lawn. “We have an opportunity to help nature in the weirdest of all ways.”