Biogeosciences News

Rock-Chomping Bees Burrow into Sandstone

A previously unknown species of rock-excavating bees, discovered 40 years ago but not reported in the scientific literature, finally gets the spotlight.


Hundreds of tiny holes spread across a sandstone cliff wall in Utah’s San Rafael desert. They weren’t carved by humans or weather. Bees did it—specifically, a bee species new to science and named Anthophora pueblo for the Puebloan sandstone cliff dwellings that dot the deserts of the southwestern United States.

“The desert is a hard place to live,” said Michael Orr, a doctoral student at Utah State University in Logan and lead author on a 12 September paper in Current Biology describing the species. “Anthophora pueblo has pioneered a suitable niche between a rock and a hard place.”

“Bees are a very conspicuous and well-studied group of insects, and the fact that we can still find these novel behaviors in bees is exciting,” said Amy Toth, an entomologist at Iowa State University in Ames, who wasn’t involved in the study.

Observing new species of bees will help to encourage more research in basic bee biology, Orr told Eos, which is necessary to help in conservation efforts. “If we don’t know how many species are out there and how they live, we can’t protect them and their varied roles in natural systems,” Orr said.

Bees spread pollen from plant to plant, helping plants reproduce, so learning about Anthophora pueblo and other bee species “is crucial for actually maintaining biodiversity,” he added.

Rocky Nests

Researcher scales sandstone wall.
Utah State University doctoral student Michael Orr scales a sandstone cliff wall to collect samples of desert bees. Credit: @DaveDenlinger

Scientists have documented bees that nest underground by excavating silt or clay, in houses or trees by digging into wood, or even in the soil near volcanoes. “Despite the fact that most bee species are found in deserts,” very few of them nest in rock, Orr said. Until now, no one has reported bees that excavate rock.

Forty years ago, a bee researcher named Frank Parker happened upon Anthophora pueblo nests in the sandstone and recognized what they were but never published his research. In 2015, Orr came across some rock samples that Parker had collected that contained tunnels excavated by the bees. Orr and Parker retraced the older researcher’s steps and found the original Anthophora pueblo nests—surprisingly still active—along with five new nests in Utah. Since then, Orr has discovered over 50 such rock nests in Utah, Nevada, California, and Colorado.

Gnawing the Stone

The bees use their mandibles to chew away at the sandstone, creating a network of tunnels. The bees also munch tiny pockets into the rock in which to gestate and nourish young bees.

The bees also collect water and use it to weaken carbonate crystals that make a cement between the grains of sand, Orr said. In fact, Orr found all the rock nests near water and even evidence of an emptied nest near a site where the water source had dried up.

It’s not unusual for bees to harness water, Toth said. Some bee and wasp species bring water to their nests to help cool them down, but she hadn’t heard of bees using water to actually build nests.

“The fact that they’re using water isn’t all that surprising, but in the context of excavation, that’s a pretty neat behavior,” Toth said.

Why Sandstone?

Discovering these bees really pushes “the limits of what we thought bees could do as far as their toughness,” Toth continued.

It takes a lot of energy to carve tunnels through sandstone, which had Orr and his team scratching their heads—why would a bee spend so much energy digging a tunnel through hard rock? Other Anthophora bees burrow into soil or clay, but this pueblo variety specifically seeks out sandstone.

It turns out, however, “that same durability that makes it harder to excavate is actually providing benefits,” Orr said. For instance, durable sandstone protects the bees from flash floods or heavy rains.

Another benefit is protection from parasites, Orr said. As bees fly from plant to plant, they accidentally pick up larvae from parasitic beetles and carry them to their nest. Sometimes the larvae end up in a nest cell, where a baby bee develops. But because adult bees build hard sandstone lids over each nest cell, the beetle larvae—hungry for nourishment—can’t get out again. Although the resident hatchling bee succumbs to a macabre fate, the rest of the nest is spared because the trapped beetle larvae can’t grow and reproduce, Orr continued.

Climate Change, Conservation

Because of the bees’ nesting limitations—ample sandstone near a water source—conservation will be an issue in the future, Orr said. Scientists anticipate that deserts will become drier as the globe warms, he continued, which could “reduce the number of water sources and could ultimately constrain where this bee can nest even further.”

Toth “wholeheartedly” agreed that prospects for Anthophora pueblo will likely worsen. “Species that are more specialized on certain kinds of habitats, or little ecological niches, those are the ones that are most susceptible to disturbances,” she said.

—JoAnna Wendel, Staff Writer

Citation: Wendel, J. (2016), Rock-chomping bees burrow into sandstone, Eos, 97, doi:10.1029/2016EO059993. Published on 26 September 2016.
© 2016. The authors. CC BY-NC-ND 3.0