Hi Hal,

Spiders are actually quite beneficial and eat a lot of insects. Also, there is only one spider in Larimer County that can be harmful to humans, which is the western widow (black widow). They tend to be shy and live in dark protected areas.

Here's our fact sheet on "Spiders in the Home": https://extension.colostate.edu/topic-areas/insects/spiders-in-the-home-5-512/

From that publication:

Controlling Spiders Around the Home

From a biological standpoint, it is rarely necessary to control spiders. However, if it is desirable to get rid of spiders in the home, a combination of sanitation and pesticides should be effective. Pesticides alone, without some effort to remove or modify favorable spider habitats, will not be effective.

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 spider webs. The elimination of other insects that are prey can limit spider development.

Occasional spiders can be removed by hand (wear gloves or trap the spider in a container ) or with a vacuum. Sticky traps, used to control cockroaches and rodents, can capture spiders when placed along baseboards or other migration areas. Spiders are most often found in kitchens, bathrooms or basements where they are seeking a source of moisture.

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 must be applied in accordance with the label’s instructions. Total release foggers, containing pyrethrins, probably will have little effect on spiders.

Where 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. Dark colored siding seems to be less attractive than white siding to the insects on which spiders feed.

Hi again,

Yes, the products containing any of the following insecticides will work on spiders: bifenthrin, cyfluthrin, permethrin, tetramethrin. You will have to read the label to find the products (like reading a nutrition label).

Read the label in its entirety--the label is the law. Do not apply on any flowering plants.