Last week, spiders descended in droves upon a town in southern Brazil — literally.
When 20-year-old web designer Erick Reis left a friend’s house on Sunday, he saw what looked like thousands of spiders overhead, reported G1, a Brazilian news site, on Feb. 8. The large, sturdy spiders were hanging from power lines and poles, and crawling around on a vast network of silk strands spun over the town of Santo Antonio da Platina.
Reis did what many of us might do: He pulled out his camera and shot a video of spiders seemingly falling from the sky.
As creeptastic is it may be, “The phenomenon observed is not really surprising,” said Leticia Aviles, who studies social spiders at the University of British Columbia. “Either social or colonial spiders may occur in large aggregations, as the one shown in the video.” The reason, she and others say, is simple: This is how they hunt.
An early report suggested the swarming spiders were Anelosimus eximius, a social species of spider that weaves communal webs, lives together as adults, and shares childcare duties.
However, it appears that initial assessment may be wrong. The spiders in the video are more likely a species of colonial spider that aggregates individual webs and lives in groups only temporarily, dispersing before reproducing, Aviles said.
“The spiders I saw in the video are not Anelosimus eximius,” said Deborah Smith, an entomologist at the University of Kansas who specializes in social spiders. She notes that A. eximius is a bit smaller than the arachnids Reis filmed, and may not live that far south. “The spiders in the video are very large and robust,” she said. “It might be worth looking at Parawixia bistriata, a large, group-living orb weaver, to see if that one fits the bill.”