Researchers have been investigating an unusual new species of bee that doesn’t build its nest in a hollow tree or dig a burrow in the soil like ordinary bees, but instead carves itself a home in sandstone cliffs. These quarrying bees live in the deserts of the American Southwest, which raises the question of why they choose to excavate nests in the tough sandstone rock rather than going for the easier-to-dig sand at the cliff's base.
“Not much is known about this hard-to-find species and our first step was to confirm it actually prefers nesting in sandstone,” explains Utah State University’s Michael Orr, lead author of the study published in Current Biology. “Once we confirmed this preference, the next step was to explore why the bees expend such tremendous effort and energy, limiting their ability to reproduce, to create these shelters.”
The bee (Anthophora pueblo) was first found to nest in the sandstone formations of Utah’s San Rafael Desert close to 40 years ago, but was quickly forgotten about in the collections of the university, until a few years ago when Orr discovered five new nesting sites for the excavating insect, including in one of the hottest environments on Earth – California’s Death Valley.
The team found that the bees are able to quarry the stone using water as an aid, which is helped by the rocks' property of weathering fairly easily. In fact, it was this factor that helped the researchers identify many of the nest sites, as they invariably found them in the sandstone monuments surrounded by pools of water. But this still didn’t answer the question of why the bees put so much effort into constructing their shelters.
“Sandstone is more durable than most other nesting options and any bees that do not emerge from these nests in a year are better protected,” says Orr. “Delayed emergence is a bet-hedging strategy for avoiding years with poor floral resources – especially useful in the drought-prone desert.” Not only that, but nesting high up on the cliffs may help protect them against flash floods that occasionally hit the deserts.
In addition, their sandstone nests may help to lower the number of parasites that live in their holes, because the sandstone contains less organic matter, meaning fewer microbes will be able to survive in them. So despite living in one of the harshest environments we know of, it seems that the little bee has got things sorted out.
Image in text: Michael Orr catching bees in southern Utah. Michael Orr/Utah State University