The false widow is a close relative of the black widow (same family) and is common in the home throughout the year. However, it is harmless to humans.

Description:

Steatoda sits on a branch in its web

Figure 1. Female Steatoda species hanging upside down in her web. Photo by R. Carlson

There are several Steatoda species present in Montana. The species Steatoda grossa and S. hespera are the most common. The adult female resembles the adult black widow in size and shape. Both the female, male, and immature false widow spiders are dark brown with variable lighter markings on the abdomen (females1/5- to 5/16-inch; males 1/8- to 1/5-inch), and no hourglass is present on the underside of the abdomen (Fig. 1). Similar to black widows and other members of the comb-footed spider family, they hang upside down in their webs and have large, bulbous abdomens.

False Widow Behavior

  • Webs are built near the ground, normally around rocks, logs, or boards.

  • Some build webs underneath overhangs around furniture and buildings.

Management:

Non-Chemical Control:

  • Modification of any of the habitat surrounding the home is critical to keep spiders from entering. Eliminateany potential burrowing sites close to the entrance of the home, including wood piles, rock piles, brush, andfirewood.
  • Install door sweeps, and seal cracks and crevices around home entrances and the foundation. Spiders canalso be removed by vacuuming. Vacuum around window wells and other entrances to reduce potential preysources and any webs that are created.
  • Sticky traps can be placed around home entrances and areas where spiders reside including crawl spaces,bathrooms, and basements. Reduce clutter in these areas to eliminate potential hiding spots.

Chemical Control:

Sprays can be used outdoors where spiders might be entering, targeting areas around entrances, including doors, windows, vents, and garages. Insecticides labeled for indoor use (mostly pyrethroids, such as those with the active ingredients bifenthrin, permethrin, and cyfluthrin) can be used as a last resort to control spiders if large numbers are present within the home. Bug bombs are not effective for controlling spiders in the home and are not recommended.

 

To learn more about the topics discussed on this page, contact the Schutter Diagnostic Lab.  If you suspect an infestation on your property, contact your local extension agent, the Schutter Diagnostic Lab at Montana State University, or the Montana Department of Agriculture.

 This November 2022 fact sheet is also available as a printable PDF (189KB).  

Disclaimer: These recommendations are provided only as a guide. It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used. The authors and Montana State University assume no liability resulting from the use of these recommendations. The Montana State University Extension Service is an ADA/EO/AA/Veteran’s Preference Employer and Provider of Educational Outreach.