About 1/4-inch in length.
This spider belongs to a family of spiders known for resting in a small silken retreat or sac during the day. The yellow sac spider is a nighttime hunter which feeds on small insects and possibly even other spiders. As they wander about in search of prey they sometimes crawl onto people sitting on a couch or lying in bed. The spider may then bite the person one or more times. The yellow sac spider likely accounts for more bites on people than any spider in the United States. Fortunately, the venom of this spider produces minimal effects. The bite usually forms a hard, reddened area that may measure from one inch to several inches in diameter, depending on the individual’s reaction to the venom. A white pustule typically forms at the bite site. Although the wound does not become ulcerating, it should be cleansed and disinfected. Any person receiving any perceived spider bite should consult a physician for treatment.
The yellow sac spider is common throughout the eastern United States, in particular from New England through the Midwest. It is normally an outdoor spider but will readily enter and breed inside homes and other buildings. The silken “sac” retreats are usually seen in corners along baseboards, along the ceiling, and beneath and behind furniture. Outdoors, the sacs will be found beneath the bark of trees and under items such as stones and logs. Sacs may also be found along soffits, beneath window sills and around door frames.
The best approach with this spider is to find, destroy and remove the sacs and the spiders hiding within. Steps to be taken to prevent new spiders from entering include: Removing or limiting heavy, ground-covering vegetation near the home. Sealing cracks and holes in the building’s exterior. Installing tight-fitting screens on all attic and foundation vents. Sealing holes around pipes indoors to prevent spiders from entering the living spaces of the home from basements and crawl spaces by following plumbing lines. Where numerous spiders and bites have occurred, a professional should be consulted to conduct a thorough inspection and recommend possible treatments.