Portland, OR

Yesterday, I wrote about spiders and the tremendous number of spiders here in Portland. After I finished that post, I ran across more information about spiders in the area, and now, I am more freaked out than ever.

**Warning: Do not read further if you get freaked out pretty easily. However, do read further if you want to learn more about a dangerous little critter that you may run across living here in Portland, Oregon.

A young female hobo spider.

The Hobo Spider is scientifically known as Tegenaria agrestis. It does have family members that look similar, and luckily one of those cousins is the Giant House Spider, which is credited with keeping Hobo spiders at bay. The Hobo got it’s name from how it spread across the US and Canada. The spider arrived from Europe in the 1930’s and made their way across the continent by hitching rides on steamer trunks and shipping crates via the railroad networks, like a “hobo.”

A distribution map of venomous spiders in the US.

In this map, the entire US is outlined with yellow and purple, which means that Yellow Sac and Black Widow spiders, respectively, are found across the country. The green area is home to the Brown Recluse. The blue area signifies the home range of other Recluses, and the red area is home to the Hobo.

The Centers for Disease Control and JAMA list the Hobo as poisonous, and though it is widely accepted that the Hobo is dangerous, there is some debate as to just how dangerous the Hobo’s bite can be. In the 80’s, a researcher found that the bite/venom produced necrotic lesions in rabbits, which backed up the ideas that similar lesions in humans could be caused by that pesky hobo. Necrotic means “dead flesh” so if this sounds similar to the much-feared Brown Recluse spider, the two spiders are pretty similar.

I did mention that there is some debate over how dangerous the Hobo bite can be. Researchers here at Lewis and Clark (as well as from University of Michigan, my alma mater) found that one) they could not replicate the same results (those necrotic lesions), and two) Hobo spiders will also inflict “dry bites” with no venom — kind of just a way to scare people and animals off without wasting precious poison. Also, over the years, no incident of necrotic lesions has been conclusively attributed to a Hobo.

The Hobo is not known to be overly aggressive toward humans, so that is a relief, sort of.

Like I mentioned earlier, the harmless but still scary looking Giant House Spider is known to prey on Hobo spiders. How ironic that a scarier and bigger spider can protect us from a smaller but more dangerous spider. Giant House spiders also came from Europe, and they are gaining ground here in the US. As there has never been a case of human fatality attributed to the Hobo spider in Europe, many scientists feel that the Giant House has always kept them in check across the pond.

Identifying the Hobo can be tricky as it looks like a lot of other spiders. First, it is a “funnel-web” spider, so if you find a bunch of funnel webs that look like silken sheets laid out horizontally in the lower bushes around your house, you could have hobo spiders, but you can also have any number of other spiders, so don’t use the web as an indicator. Here is a great article on identifying the Hobo.

Portland, Oregon, spiders, Hobo, Brown Recluse, Giant House, Black Widow, Yellow Sac, necrotic lesions, dead flesh, funnel web, Centers for Disease Control, JAMA, Lewis and Clark College, University of Michigan, venomous spiders, poisonous spiders, US