
NPS- Montezuma Castle NHS
There are many species of spiders in Idaho and only a few are venomous (where their bite would be a danger to humans). Most spiders are very beneficial and are favored diets of birds and other animals we enjoy watching. Spiders, like all animals in the park, are protected by law. Please watch for them and leave them alone.
Hobo Spiders
NPS fact sheet on hobo spiders explains what to look for and what to do if you get bitten. These species were originally from Europe. It is believed that they were transported to the US via shipping lanes and ended up in Seattle, WA in the late 1920s. They have since expanded slowly throughout the Northwestern US and Western Canada. Their bites have often been confused with the brown recluse; therefore, public awareness of the hobo spider is low.
Black Widow Spiders
The black widow spider (Latrodectus spp.) is notorious for its neurotoxic venom. Adult females are shiny black with a red hourglass marking on the bottom of their abdomens. Males are half the size of the female, usually dark brown and have no hourglass mark. (Black Widow spiders and general pest managment of spiders is a concern at many National Park Service areas.)
Brown Recluse Spiders
Known primarily for the flesh-eating properties of its venom, the brown recluse is a uniform brown color and can be identified by the dark brown, violin-shaped pattern violin that surrounds its six eyes. Fear of the brown recluse bite often leads people to wrongly identify other benign spiders as brown recluse. The brown recluse spider is often encountered hiding in cool dark places during the day -such as inside folded clothes or under logs- but is most active at night. This spider is not aggressive and usually only bites when accidentally pressed against human skin. (thank you to Amistad and their Field Guide to Spiders)
Yellow Sac Spiders
Cheiracanthium inclusum is very common in most of the United States. The yellow sac spider is a cause of many bites in the U.S., and a lot of house spiders are crushed on suspicion of being yellow sac spiders. Its bite correspond in pain to a bite from a wasp. Details about this spider and others can be found at venomousspiders.net.