One Quick Question: Why are there suddenly so many spiders?
As the weather drops and Halloween quickly approaches, we start to see a lot more spiders pop up around town — both as decoration and the live ones who’ve decided to make themselves our newest, uninvited roommates.
Spiders’ connection with Halloween is not new. They were considered companions of witches during medieval times, and some believe if you spot a spider on Halloween night, it means the spirit of a deceased loved one is watching over you.
It’s a nice thought, but it might not help much when a two-inch, eight-legged beast is staring at you from your shower. So, what should we do when we encounter one of these “creepy crawlies”?
We asked entomologist and Professor of Biology Merrill Peterson: Why do we see more spiders in the fall, and what should we do if they come into our house?
“Washington is home to an incredible, underappreciated diversity of spiders – at least 900 spider species reside in the state! The great majority of these are tiny spiders that have specific habitat requirements such as living only in alpine rockslides, sphagnum bogs, rocky desert ridges, or mossy rainforests. Relatively few species thrive in urban settings, and many of these are non-native species that were inadvertently transported in shipping containers and subsequently became established in and spread throughout our region.
The perception that spiders are more prevalent in fall is largely due to some of the largest, most conspicuous of these introduced species becoming mature in the fall. Indoors, the large, “hairy” spiders that you find at this time of year are likely introduced funnel weaver spiders such as the Giant House Spider and the Hobo Spider. These fast-moving spiders live both indoors and outdoors, residing in funnel-shaped webs they build in gaps in walls, stacks of firewood and other crevices. They reach adulthood in fall, so not only is this when they are at their largest, it is also when males are more likely to wander in search of mates.
Large spiders wandering about our homes leave a big impression! Also, Hobo Spiders have a bad rap as the cause of nasty bites that can take a long time to heal, but despite lots of research on the topic, there is little evidence that Hobo Spiders are actually dangerous to people.
If you don’t like living among Giant House Spiders and Hobo Spiders, it’s fine to release them outdoors, as they will likely find another crevice in which to create a new web. However, it is important to keep in mind that spiders thrive indoors by eating insects and other invertebrates – if it weren’t for spiders, you would see many more of these other critters in their place.
Outdoors, another introduced spider that becomes much more conspicuous in fall is the Cross Orb Weaver. Although these spiders are around all spring and summer, they only become noticeable after the females begin to grow rapidly in late summer prior to breeding. At this time of year, Cross Orb Weaver females sit at the middle of the large webs they suspend between trees and shrubs – these are classic spider webs (think Charlotte’s Web) that may be covered in dewdrops on cool fall mornings. The males are tiny by comparison to the females. During the fall mating season, their efforts to court females are perilous, as the female may prefer to eat the male rather than mate!”
If you are interested in learning more about spiders and other “creepy-crawlies,” come to the WWU Insect Collection Open House 1 – 4 p.m. on Saturday, Oct. 18, on the bottom floor of the Biology Building (see https://biology.wwu.edu/insect-collection-open-house for details). Another great resource is Merrill Peterson’s Pacific Northwest Insects field guide, available online or via your local bookstore.
Mikayla King (‘17) covers the College of Science and Engineering and Woodring College of Education for the Office of University Communications. Reach out to her with story ideas at kingm24@wwu.edu