Arachnids (Spiders, Scorpions)

Spiders in Utah

 Click here to download a PDF of USU Cooperative Extension publication Spidersn-2012

Spiders are arachnids, a group that includes other 8-legged arthropods like ticks, mites, sun spiders, scorpions, and harvestmen (daddy longlegs). There are approximately 621 species of spiders known to occur in Utah (*Allred and Kaston, 1983). Spiders are beneficial predators and the majority of them are harmless to humans. Much fear of spiders results from the few species that can be dangerous to humans, such as the black widow and brown recluse (which does not occur in Utah), and from the many false facts and myths about spiders. The majority of spiders have weak venom and are only capable of harming small prey that they subdue and consume. If bitten by one of these spiders there may be some slight irritation and swelling similar to a mosquito bite or bee sting. The major spider of medical concern in Utah is the black widow.

*Allred, D.M., and Kaston, B.J. 1983. A list of Utah spiders, with their localities. Great Basin Naturalist, April. Vol. 43, No. 3: pp. 494-522.

Spider Bites

Black Widow

  • If you experience a spider bite, you should catch the spider for identification. Finding a random spider in the house after a mystery skin irritation occurs does not implicate the spider.
  • Clean and disinfect the bite using a topical antiseptic, and cover with a sterile bandage.
  • Monitor the bite and visit your doctor if symptoms progress.
  • Secondary bacterial infections are possible after any spider or insect bite, and can become serious if left untreated.

(January 2013 Utah State University Extension and Utah Plant Pest Diagnostic Laboratory ENT-163-12PR)

Fall is the season for spider encounters in Utah. Many spiders are nearing the end of their life, searching for mates and laying eggs, habits that usually increase the chance of human-spider interactions.

The most frequently encountered group is the funnel-web spiders, which includes the hobo spider.
(January 2013 Utah State University Extension and Utah Plant Pest Diagnostic Laboratory ENT-163-12PR)

Hobo Spiders:



Tarantulas are rarely seen since they spend most of their time underground. Utah is on the northern border of the tarantula’s native range, but at times, these spiders can be found as far north as Cache County. In the fall, male tarantulas leave their underground burrows and migrate in search of female mates, sometimes into home landscapes. The genus of tarantula found in Utah (Aphonopelma) is not harmful to humans.

Spider Management

  • Seal all cracks and crevices (foundation, etc.) leading into the home with silicon caulk or sealant.
  • Install weather stripping around doors and windows, especially all doors leading to the outside, including the garage door.
  • Make sure door sweeps are in good repair and come in contact with the floor or threshold and both sides of the door frame. Even a gap a few millimeters wide/high can allow spiders access to a home.
  • Spider and insect sticky traps can be used near doorways, baseboards and windows to trap spiders. – In inaccessible voids an insecticidal dust/silica formulation can be useful. in keeping out spiders.

Cleaning and Habitat Modification

  • Vacuum regularly. Spiders, webs, and egg sacs can be vacuumed, directly eliminating spiders (except hobo egg sacs, which are found outdoors).
  • Minimize clutter. Spiders love secluded places to hide and lay egg sacs. Simplify the environment inside by cleaning regularly and storing clutter in sealable storage bins. Outside, move rock and wood piles or anything that creates spider habitat away from the home.
  • Change exterior lighting. Insects are attracted to exterior lights at night, which in turn will attract spiders looking for food. Replace regular light bulbs with sodium vapor lights which are less attractive to insects.

Scorpions in Utah

Video by Tom Perkins

 Click here to download a PDF of USU Cooperative Extension publication: ENT-68-08.pdf

There are approximately 9 species of scorpions in Utah. Scorpions are usually found in semiarid deserts. Most Utah scorpions are found in the southern part of the state; however, three species are occasionally found in northern Utah. Scorpions are nocturnal. They find shelter during the day and come out at night to feed. Overall, scorpions have flattened bodies in which they can easily fit under stones and wood. They tend to hide under boards, in stacked lumber, firewood piles, attics, and in debris. Scorpions can enter homes through very small openings in windows and doors. All scorpion species possess venom. Most scorpion stings are relatively harmless to humans. The only species in Utah that is potentially harmful to humans is the Arizona bark scorpion. They have a very limited distribution in Utah, and are usually found only in the south eastern part of the state (Kane county). Children and older adults are more likely to exhibit symptoms if stung. People stung by a scorpion should consult a doctor. The individual reaction to the venom can vary greatly.

To minimize scorpions around a home:

Scorpion NPS

  • Eliminate favorable habitat.
  • Do not keep shoes, boots, clothing items, or wet towels outside.
  • Clean up any debris around the house.
  • Bring firewood inside only when it is immediately going to be burned.
  • Wear gloves and boots when cleaning areas where scorpions may hide.

(Utah State University Extension and Utah Plant Pest Diagnostic Laboratory ENT-68-08 June 2008)

Bark Scorpion

If you have a problem with arachnids that cannot be resolved by following these tips consult a professional, licensed pest control company.