by Katherine J. Wu in the NYT
Shortly before Halloween in 2018, an administrative building at Glacier Bay National Park & Preserve in Alaska began to sprout a beard.
But the strands that composed the furry fringe weren’t fine brown hairs. They were the spindly legs of hundreds of tightly clustered daddy longlegs, letting their glorious gams dangle free.
Park officials snapped photos of the spookily well-timed growth and posted them to Facebook and Twitter, and shared them again this sinister season, terrifying onlookers anew.
The ability of Opiliones species, also known as harvestmen, to form these woolly knots has fascinated arachnid enthusiasts for years. But “we still don’t really know what triggers these aggregations,” said Mercedes Burns, an evolutionary biologist who studies the eight-legged creatures at the University of Maryland, Baltimore County.
One leading hypothesis posits that Opiliones get together to keep from drying out when humidity levels drop in the summer or fall, Dr. Burns said. As their nickname implies, most daddy longlegs are built like grains of rice buoyed by super-skinny stilts, saddling them with “a big surface-area-to-volume ratio problem,” she said.
With few spots to store water and plenty of places from which to lose it, the arachnids rapidly parch. Hunkering down together creates a microclimate for the arachnids, not unlike a sweaty locker room, that can stall the desiccation process.