Millions of spiders have appeared in a web at least a half mile long in North Memphis, Tenn.

The Washington Post reports that town residents are frightened, but that the occurrence isn’t a dangerous one. It’s part of “ballooning,” where young spiders float away.

“Young juvenile spiders of most families disperse by sending out a swath of silk threads that may be over a meter in length,” Susan Riechart, a professor at the University of Tennessee Knoxville and former president of the American Arachnological Society, told The Post. “Particular air currents favor ballooning. This would explain the fact that thousands to hundreds of thousands may take off at the same time. Caught by the air currents, the spiderlings have no control over where they will land, but it is not surprising that they may fall in the same area.”

Riechart also said the spiders in Memphis appear to be “harmless,” but that hasn’t stopped residents from wishing away their new neighbors.

“You can’t even sit in [a neighbor’s] house because they’re all on the wall, on the door. We been killing spiders for about an hour now,” Debra Lewis told WMC Action News 5 of her neighbor’s house.

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Write to Tessa Berenson at tessa.berenson@time.com.