Sac spiders can be found walking about on foliage; under leaf litter, stones, and boards; on buildings, under the windowsills and siding; and in the corners of walls and ceilings within homes. Introduced species from Europe, was found throughout much of the Northeast as of 1978. It has substantially increased its range since that time. 3/16 to 15/64 in length and coloration is a light yellow to cream color. Has a slight greenish tinge to its abdomen and a pale-yellow cephalothorax, and a slightly darker dorsal stripe running lengthwise down the abdomen

Sac spider retreats may be found under objects outdoors or in the corners of walls and ceilings indoors. These retreats are silken tubes or sacs in which the spiders hide during the daytime and also lay their eggs. In homes with light, neutral-colored walls and ceilings, the retreats may go unnoticed, as they are small and blend in with the background coloration. Prowling spiders are "active hunters," searching for prey rather than capturing it within a web. During these nighttime forays, the spiders encounter humans and bite when they become trapped between a person's skin and sheets, clothing, shoes, and so forth.

Medical Importance: Sac spiders probably account for a significant number of human bites. Although most of these bites are painful at the outset, they normally do not result in any serious medical conditions. The bite is usually very painful with developing redness, swelling, and intense itching. Some patients may exhibit systemic reactions with fever, malaise, muscle cramps, nausea, sore throat, tremor, and vision changes. These symptoms are similar to those from a black widow bite but much less severe. A necrotic lesion rarely occurs and is much smaller and less severe than a brown recluse bite. Symptoms resolve in 6 to 9 days.