Katie Orlinsky/New York Times

Arctic bumble bees isolate their feces in an 'outhouse' external to the main nest

February 8, 2024

Bumble Bee Hygiene: Cornell Researchers Observe ‘Outhouse’ Structure in Arctic Nests

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Cornell researchers recently observed a novel ‘outhouse’ structure in Arctic bumble bee nests that could mitigate the spread of fecal-borne disease within bee colonies. 

The outhouse is a small and damp subterranean cavity separated from the main structure of a bee nest by a small barrier. In a recent study, Leah Valdes grad and Hailey Scofield grad, who took a leave of absence to establish a honeybee technology business, found that the outhouse cavity was the only area of the nest that contained fecal matter — a feature that had not been previously observed in a wild bumble bee nest. 

Separating feces from the colony may reduce the spread of intestinal parasites such as Crithidia bombi, a common parasite in bumble bees that spreads through contact with contaminated feces. Pathogens like Crithidia adversely impact colony health and exacerbate the negative effects of pesticides and nutritional stress.

Disease is one of the primary contributors to the global decline in bee populations and diversity. However, there remains significant gaps in research about disease transmission within bumble bee colonies, whose underground nests are hard for biologists to locate and study, according to Valdes. Arctic bumble bees in particular receive even less research attention. 

“These big, fluffy [Arctic] bees do most of the pollination in high latitudes — they can fly when it’s cold, unlike little solitary bees,” Valdes said. “Even though they do most of the pollination, we know little about them.”

In a follow-up statement to The Sun, Valdes clarified the importance of other pollinators as well as bumble bees.

“Bumble bees are often the most abundant pollinators in the low arctic, but mosquitos and flies become more important in the high arctic,” Valdes wrote. “I don’t think anyone’s thoroughly quantified how much pollination different insect species do throughout the Arctic … Bumble bees are among the most important pollinators in the arctic — along with flies and mosquitos.”

Valdes and Scofield unintentionally stumbled across a wild bumble bee nest while in Alaska to collect individual bees.

“While we were walking along, we stepped on a pile of moss and it buzzed at us,” Valdes said. “We immediately knew we had found something and dug in.”

The initial discovery of the bumble bee nest prompted a systematic search of the area. Ultimately, the researchers found ten colonies in total, which they gently removed from the ground and placed in boxes — live bees and all — to fly back to a lab in Los Angeles.  

At the lab, Valdes and Scofield let the bees operate as normal while they conducted behavioral studies, recording where the bees defecated and taking detailed notes of nest size and outhouse structure.

The researchers noticed that even in the absence of a physical outhouse structure, worker bees continued to isolate their feces outside of the main nest cavity. This methodological isolation of feces is an evolved social immunity behavior — a conduct that highly social insects use to defend themselves against disease transmission. 

Insects that practice hygienic behavior are not new — well-studied species like honey bees are known to defecate exclusively outside their nests to prevent the spread of fecal-borne disease. These bees even strategically postpone defecation until warmer winter days when they are able to leave their hive without freezing.

However, the examination of social immunity behavior in bumble bees — which are larger and hairier than honey bees — has not been as extensive, with prior research focusing on the spread of disease via flowers rather than within the colony. Valdes and Scofield address this gap and provide insight into inter-colony disease transmission. 

“Our study shows one way that [Arctic bumble] bees can defend themselves behaviorally against disease, suggesting that they might be able to slow the spread of disease within the colony,” Valdes said. 

The findings serve as a foundation for future lab experiments to explore the role of the outhouse in slowing disease spread. As a part of the McArt Lab, Valdes has begun conducting manipulative studies based on this initial research, analyzing how the presence of outhouse structures affects the amount of pathogens in the colony and the rate of transmission. Valdes is also overseeing field-based research to see how evenly disease is distributed across bumble bee colonies. 

Though the research enhances understanding of bumble bee nesting and hygienic behaviors, the discovery of Arctic bumble bee nests was itself rewarding, according to Valdes.

“It’s really difficult to find wild bumble bee nests, which has caused a big gap in conservation efforts and curiosity of how these insects live,” Valdes said. “Finding the nests was a really shocking, exciting moment.”

Ellie VanHouten can be reached at [email protected].

Correction, Feb. 10, 12:18 a.m.: A previous version of this article incorrectly stated that Hailey Scofield graduated with a Ph.D. in 2020. Scofield took a leave of absence to establish a honeybee technology business and has not finished her Ph.D. The Sun regrets this error, and the article has been corrected.

Clarification, Feb. 10, 12:18 a.m.: This article has been updated to include more information about the importance of bumble bees as pollinators relative to other animals.