It's pretty normal for spiders to wander indoors in the early fall when cooler outdoor temperatures force them to find shelter, so don't be surprised if you notice a spider or two trying to set up residence inside your house during the next few weeks.
Common spiders found indoors include funnelweb spiders, cobweb spiders, cellar spiders and sac spiders.
There are a few spiders whose bite requires medical attention, including the black widow, brown recluse and a newcomer called the Hobo spider.
A European species of funnelweb spider, known as the 'Hobo spider' (Tegenaria agrestis), is slowly spreading across western North America and was recently found in Colorado. Some reports indicate bites of this spider may produce wounds similar to that of brown recluse.
Be sure you and your family members know how to identify these poisonous spiders, and be watchful for them when working in favorable spider habitat areas such as rock or wood piles, sheds, basements, crawl spaces, garages, wells and storage buildings.
If you aren't willing to share your living space with spiders, a combination of sanitation and pesticides may be necessary to manage them. Pesticides alone, without some effort to remove or modify favorable spider habitats, will not be effective. For best control of spiders in and around your home:
• Remove rocks, wood piles, compost piles, old boards and other sheltering sites adjacent to the home.
• Eliminate migration of spiders into homes by caulking cracks and crevices around the foundation.
• Make sure all screens and doors are sealed tight.
• Keep crawl spaces free of debris and limit boxes and other potential hiding places from basements and other dark storage areas.
• Regularly vacuum or brush away spider webs.
• Eliminate other insects that spiders can prey on.
Residual insecticides can be used to control spiders when applied to corners and other sites where spiders tend to breed. Household insecticide products containing various pyrethroids (bifenthrin, cyfluthrin, permethrin, tetramethrin) are commonly available for this purpose and should be applied in accordance with the label's instructions. Total release foggers, which contain pyrethrins, probably will have little effect on spiders.
When spiders and webbing occur in nuisance numbers on the outside of buildings, they can be washed off with a forceful jet of water. Reduction of outdoor lighting or replacing lighting with yellow or sodium vapor lights that are not attractive to insects can limit spider web building.
For more information, including color photos and descriptions of Colorado spiders, refer to CSU fact sheet number 5.512 "Spiders in the Home" online at http://www.ext.colostate.edu/pubs/insect/05512.html or available at the CSU Moffat County Extension Office, 539 Barclay Street, 824-9180.