Fall is the season for spider encounters in Utah. Many spiders are nearing the end of their life, searching for mates and laying eggs — all habits that can increase the chance of human-spider interactions. Below is a description of the spiders commonly found in Utah in the fall and methods for encounter prevention.
 
 * Western black widow – The major spider of concern in Utah can be identified by the red hourglass shape on the underside of the abdomen. Male black widows are much smaller and have brown, cream and white coloration. Immature females have black, red and white coloration and become black when they mature. Despite the widow’s name, male spiders are rarely eaten after mating. A bite from a female black widow can result in pain at the bite site, increased body temperature and blood pressure, profuse sweating, nausea and tightening of the chest and muscles. Contact a doctor or hospital if you have been bitten, and collect the spider for identification. Fortunately, black widows are not aggressive, but will defend egg sacs in their webs. 
 
 * Hobo spider – By far, the spider most commonly seen indoors in fall is the hobo. Populations are large in northern Utah, and when male spiders leave their webs in search of mates, they often find their way inside. The Utah Plant Pest Diagnostic Lab (UPPDL) recently created a website that addresses most hobo questions. It is available at https://utahpests.usu.edu/uppdl/hobo-spiders.
 
 * Wolf spiders – These ground hunting spiders pursue prey in lawns and gardens and do not spend much time in webs. Female wolf spiders may be seen with their egg sacs attached to the rear of their body. When the eggs hatch, the small spiderlings climb up on the mother’s abdomen and stay for about a week. Large spiders in the genus Hogna can cause concern, but wolf spiders are not a human health threat.
 
 * Banded orb-weaving spider and cat-face spider – The adult female banded orb-weaver has a large, oval-shaped abdomen adorned with black, yellow and white stripes and black bands on the legs. The cat-face female has a large, oddly shaped abdomen that resembles the face of a cat. These spiders are attracted to garden areas and porch lights where their perfectly shaped orb webs pluck flying insects from the air. This time of year, females can mistakenly wander inside homes in search of a site to lay eggs. After the eggs are laid, females will likely die. The eggs will hatch next spring, and spiderlings will climb up structures and plants, release long strands of silk and “balloon” away in the wind to new sites.
 
 * Golden huntsman (giant crab spider) – This is the most common huntsman spider identified by the UPPDL. These large spiders are a beautiful gold color with black mouthparts and dense black hairs on the end of their legs, giving the appearance of dark socks. These “socks” allow this spider to climb up almost any surface. They are commonly found under the bark of trees or in narrow, secluded places.
 
 * Tarantula - Utah is on the northern border of the tarantula’s native range, and at times, the 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 is not harmful to humans.
 
Consider the following control techniques for spiders that may wander indoors.
 
  • Seal all cracks and crevices leading into the home with silicon caulk or sealant.
  • Install weather stripping around doors and windows, especially doors leading to the outside, including the garage door.
  • Vacuum regularly. Spiders, webs and egg sacs can be vacuumed up, directly eliminating spiders.
  • Minimize clutter. Spiders love secluded places to hide and lay egg sacs. Outside, move woodpiles or anything that creates spider habitat far away from the home. Indoors, keep clutter to a minimum.
  • 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, as they are less attractive to insects.
  • Sticky traps can be placed around baseboards to help determine types of spiders and where they are coming from. For hobos, pheromone traps are effective, but may attract more spiders to the area, including from outdoors. Avoid using pheromone baited sticky traps from August to October in Utah.
  • From August through October, remove skirts on beds and pull the bed about 8 inches from the walls to prevent wandering spiders from climbing the bed.
  • Take caution when picking clothes up off the floor or in laundry baskets where hiding spiders can be mistakenly grabbed, resulting in a bite.
  • Keep children’s toys off the floor where spiders can hide under them.
 
If you have an infestation of spiders, try the following techniques.
 
  • In secluded areas (crawl spaces, cracks or any area where people won’t come in contact with chemicals), use a dust formulation of an insecticide like TriDie.
  • Liquid or dust insecticides may be applied directly to webs (this works especially well for black widow spiders).
  • Non-residual aerosol sprays can be sprayed directly onto spiders.
  • If an outside treatment for hobos is warranted, insecticide sprays work best when egg sacs are hatching, typically from mid May to mid June in northern Utah.
 
For more information on common Utah spiders, visit the UPPDL Top 20 Arachnids web page athttps://utahpests.usu.edu/uppdl/top-20-arachnids.
 

By: Ryan Davis - Nov. 7, 2014