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Posted by: Dennis Hinkamp on Sep 1, 2012

Should I Worry About Hobo Spiders?

Contact: Diane Alston
  Utah State University Extension entomologist
  Phone: (435) 797-2516
  E-Mail: diane.alston@usu.edu
   
  Julene Reese
  Utah State University Extension writer
  Phone: 435-797-0810
  E-Mail: julene.reese@usu.edu


Ask a Specialist: Hobo Spiders: How Much of a Concern Are They?

LOGAN, UT – Hobo spider season has arrived in northern Utah. From August through October, male hobo spiders go in search of mates and frequently migrate indoors. Submissions of spider specimens to the Utah Plant Pest Diagnostic Lab at Utah State University peak in the late summer and early fall. The top arthropod submitted to the lab is the hobo ? about 650 specimens since it was first detected in the state in 1990. Many people have an intense fear of hobos, but spider experts are questioning whether they really can deliver as nasty of a bite as has been feared. 
 
Since most people do not see what has actually bitten them, there are few documented observations of hobo spider bites. Recent evidence in entomological and medical literature suggests that in most cases, hobo spider bites probably do not cause necrosis, or death of body tissue. There are multiple factors that influence the severity of a bite, including the spider sex, age, amount of venom injected, location of the bite on the person’s body and sensitivity to the venom. Hobo spiders flee danger and can run at a speed of up to 40 inches per second, are poor climbers on smooth surfaces and are unlikely to bite humans unless threatened, e.g., being trapped between clothing and skin. Although hobo spiders can be abundant, the chances of being bitten are relatively low.
 
Hobos build funnel-shaped webs and wait in the small hole at the bottom for prey to contact the silk fibers. They live outdoors in log piles, in holes in block walls, under dense vegetation, under rocks and in other protected sites. They enter buildings under doors, through foundation cracks and vents and are most often found in the basement and on the ground level. Indoors, they hide in dark, protected places, such as behind and under furniture and appliances, in corners behind doors and under piles of clothing or blankets.
 
Reducing spider populations indoors requires consistent effort. Consider these key management steps.
 
• Exclusion: seal all foundation cracks and crevices with silicon caulking. Install weather stripping around doors and windows.
 
• Cleaning and habitat modifications: vacuum regularly to remove spiders, webs and insects that spiders prey on. Keep furniture away from the wall and vacuum behind furniture, door jambs and other dark, protected places. Minimize clutter and hiding places. Replace exterior light bulbs with sodium vapor lights since these attract fewer of the insects spiders prey on.
 
• Monitoring: place sticky traps along the baseboards near “hot spots” such as near exterior doors, behind door jambs and furniture.
 
• Chemical treatment: spiders walk on their claws so their bodies have minimal contact with treated surfaces; therefore, chemical treatments work best when applied to tight spaces and to the spiders and webs directly. Avoid treating sites where humans may contact sprays and residuals. Treat crawl spaces and exterior foundation cracks and crevices with dust or aerosol formulations of insecticides such as pyrethrin (e.g., Tri-Die). Apply exterior insecticides in May and June when hobo spider eggs hatch. Indoors, apply non-residual aerosol sprays to webs and spiders.
 
• Avoid bites: from August to October when hobo spiders are most active indoors, be sure that beds are at least 8 inches from the wall, remove bed skirts, keep children’s toys picked up and avoid piling clothing or blankets.
 
For more information, visit the hobo spider page on the USU Extension Utah Plant Pest Diagnostic Lab website at http://utahpests.usu.edu/uppdl or see the spider fact sheet at http://extension.usu.edu/files/publications/factsheet/spiders-2012.pdf. The diagnostic lab provides identification of spiders and other arthropods (insects, ticks, etc.) for a $7 fee. If you experience symptoms from any kind of arthropod bite, visit your doctor for prompt treatment. Despite all the “scary news” about spiders, remember that all spiders are beneficial to humans. They are predators on arthropods that we don’t want in our homes and gardens, and spiders produce silk, venom and other products that have improved our lives.
 
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Direct column topics to Julene Reese, Utah State University Extension writer, Logan, Utah, 84322-4900, 435-797-0810, julene.reese@usu.edu.

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