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Scientists investigate rare bee that nests in sandstone

Scientists found five new sandstone nesting sites in Utah, California and Colorado, including several at the Puebloan cliff dwellings in Mesa Verde.

Brooks Hays
An Anthophora pueblo bee emerges from its sandstone nest in south central Utah's San Rafael Swell. Photo by Michael Orr/Utah State University
A new study has revealed the architectural secrets of a rare bee species that excavates its nest in the sandstone formations of the U.S. Southwest.
Scientists have been aware of the diminutive Anthophora pueblo bee for several decades, but little was known about its behavior. Recently, researchers at the Utah State University set out to understand why the elusive bee chooses to build its home in sandstone -- and not a more easily penetrated surface, like loose soil or dead wood.
"Not much is known about this hard-to-find species and our first step was to confirm it actually prefers nesting in sandstone," lead researcher Michael Orr, a USU doctoral student in biology, said in a news release. "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 bees use water to excavate their sandstone abodes, so Orr and his research partners surveyed for Anthophora pueblo nests near water sources. They found five new sites in Utah, California and Colorado, including several at the Puebloan sandstone cliff dwellings in Mesa Verde.
The new analysis, detailed in the journal Current Biology, suggests the sturdier, more insulated homes offer Anthophora pueblo larvae a better chance of survival. Whereas most bees emerge over the course of a single year, Anthophora pueblo bees emerge over four years.
"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," Orr explained. "Delayed emergence is a bet-hedging strategy for avoiding years with poor floral resources -- especially useful in the drought-prone desert."
As Orr and his colleagues told attendees of an Entomological Society of America meeting earlier this year, the sandstone also offers protection against floods and parasites. Though hardness is a limiting factor, and construction of sandstone homes require more energy, evidence suggests the benefits outweigh the costs.

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