October 01, 2010

Q: Are there more big spiders now than usual?

The Burke Museum partners with the Seattle PI's Big Blog to answer commonly asked questions about the natural and cultural history of our region. Read past entries from the Ask the Burke column here.

The following was posted to the Seattle PI's Ask the Burke column on Oct. 1.

Q: Are there more big spiders now than usual? I seem to be constantly running into webs on my outdoor walks.

A: (From Rod Crawford, curator of arachnids at the Burke Museum)

This answer is specific to the Seattle area; different places have different spider species with different population cycles.

The spiders you're "running into" are mainly one species of non-native orbweaver: the "cross orbweaver" Araneus diadematus, which is native to Europe (first record of a cross orbweaver in Washington is 1927). Orbweavers are the spiders that make orb webs, and are the only spiders that do so. They are not dangerous to humans. The population dynamics of this one species are far from typical of all spiders. The vast majority of spiders actually "lay low" in August and September because of low moisture availability in their habitats.

So, are cross orbweavers more abundant this year than usual? Well, I've been working on spiders at the Burke Museum for 39 years now... and every single year I've had someone ask that question! They can't be more numerous every year than every other year, but populations do have ups and downs within individual neighborhoods. Beyond that, I think the biggest factor is that once your eyes begin to notice spiders (which are always common), you're naturally going to notice them everywhere.

To find the answers to more frequently asked questions about spiders, visit our Spider Myths website.