Mass gatherings are common across many animal species. These aggregations may take place for a range of reasons, from group defence and thermoregulation to mating and access to resources. Snakes, for example, sometimes come together en masse when hibernating or during periods of gestation.
Now, a new study published in the journal Ecology and Evolution suggests that prairie rattlesnakes – a species of venomous pit viper native to the western United States – may form groups for another reason: to shed their skin.
The researchers believe this is the first time aggregation during ecdysis (the process of shedding or moulting skin) has been documented in prairie rattlesnakes.
The study’s lead author Emily Martin, a member of The Wildlife Society (TWS) and a PhD candidate in biology and natural resources at the University of Idaho, first noticed the behaviour in 2024 while tracking translocated prairie rattlesnakes in Sinks Canyon State Park, Wyoming, USA.
“We would find piles of rattlesnakes, and one or two of them would be shedding,” says Martin in an article published on the TWS website. Intrigued by the behaviour, she continued to track the rattlesnakes, observing numerous shedding aggregations.
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In the new study, Martin and her supervisor Courtney Conway, a biologist at the U.S. Geological Survey’s Idaho Cooperative Fish and Wildlife Research Unit and a TWS member, document the behaviour.
Of the 24 aggregations analysed, most contained two rattlesnakes, while some had three or four. The researchers found that shedding snakes were more likely to be found in gatherings than alone.
Martin and Conway aren’t sure exactly why these snakes come together to shed, but they do have several theories.
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The aggregations may take place as a form of protection from predators. “During the later stages of ecdysis, snakes experience impaired visual acuity [their eyes get cloudy] and reduced overall activity,” say the authors in the study. The combination of muted eyes and reduced movement may make them less visible to predators and therefore increase their survival rate.
Another theory is that they facilitate reproduction. Perhaps, as the snakes shed, they release pheromones to show potential mates that they are available. Or it may be the case that the snakes aggregate to mate and that the shedding follows.
Thermal regulation is another possible reason for the gatherings. “Aggregated snakes have higher thermal inertia than solitary snakes, and rattlesnakes may be more sensitive to thermal variation during ecdysis,” say the authors. “By aggregating during ecdysis, rattlesnakes could buffer against thermal instability.” So, when snakes aggregate, they are possibly protecting themselves from temperature shifts.
Martin and Conway say that other pit viper species, including midget faded rattlesnakes, northern Pacific rattlesnakes and cottonmouths, have also been observed forming shedding aggregations.
Whatever the reason for the behaviour, the discovery provides valuable insight into the lives of prairie rattlesnakes, which may be used to help inform conservation methods – for example, how best to conduct translocations.
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