Spider season arrives in western WA: Why webs are everywhere this fall

Just as the weather starts to turn, the spiders begin to come out. Spider season has arrived for western Washington.

“I moved from a place that had its fair share of different, more dangerous spiders, but the abundance was nothing like it is here,” a new Seattle resident wrote on Seattle Reddit. “True, I probably should’ve anticipated it moving to a climate like the PNW but wow it feels like they’re everywhere. As soon as fall hit, they are setting up shop all over the place. I counted over 40 webs of all shapes and sizes with all kinds of spiders on a walk with my dog earlier and that’s just what I could see.”

The top reply? “Welcome to spider season.”

Why spiders flock the state this time of year

The primary reason for the sudden surge of spiders by early fall is that it is their mating season, and the cross orb weaver and common or giant house spider — two of the most common spiders in Washington — reach maturity and are at their biggest in size by this time. The giant house spider can grow to have a body length of one inch, with its legs growing up to four inches long.

“They leave their webs and start running around looking for mates,” Rod Crawford, the curator of arachnids at the University of Washington’s (UW) Burke Museum, previously told KIRO Newsradio. “If you wanted to be a little colloquial, you might say they’re cruising for chicks.”

Spider season in Seattle varies every year, but generally occurs in early autumn within a mid-late August to mid-November window. The length of each season is directly related to how quickly temperatures drop once summer ends.

Other common spiders in the region are the false black widow, the hobo spider, daddy longlegs (also known as a long-bodied cellar spider), mouse spider, Sierra dome spider, Western black widow, wolf spider, the Northern yellow sac spider, and the zebra jumping spider.

The Washington Department of Health only lists two spiders of any “medical significance” to humans: the black widow and the yellow sac spider. Black widow spiders are common in Eastern Washington, while just a few small populations of black widows exist in the western half of the state. Female black widows are normally shiny black with a red hourglass marking on the underside of their abdomen. The marking can also be yellowish-orange, and its shape can vary, resembling an hourglass, two marks, or a single dot. The body of an adult female is relatively large, about a half-inch long.

Yellow sac spiders, meanwhile, mainly stay outside in gardens during the warm season, but can make their way indoors in the fall. Indoors, they are often found along walls and ceilings and, instead of creating webs, yellow sac spiders build small silken sacs where they hide during the daytime.

As for the rest of the spiders native to the area, Crawford explained they’re pretty much harmless — including hobo spiders, contrary to popular belief.

“In any case, house spiders are mostly harmless and beneficial. Human property rights mean nothing to other species,” Crawford said. “There was a spider habitat for millions of years where your home is now. My advice is, ‘Just wave as they go by.'”

Frank Sumrall is a content editor at MyNorthwest. You can read his stories here and you can email him here.