Yellow Sac SpiderYellow Sac Spiders

Order: Araneae
Family: Clubionidae
Scientific Name: Chiracanthium spp. and Trachelas spp.
Color: Pale yellow to pale green or orange brown to reddish
Legs: 8
Shape: Typical spider
Size: 1/8-5/16" long
Antennae: No
Flight: No

The common name comes from the retreat they build which is a flattened silk tube or sac where they spend most daylight hours; they do not build webs. These spiders are more than nuisance pests because 3 species are probably responsible for a great many cases of indoor spider bites.

Normally, these are outdoor spiders, but sac spiders often invade structures. Their numbers increase significantly in the fall when the weather turns cool and their food supply disappears. If there are small insects available, sac spiders can become established indoors.

At night, sac spiders actively hunt their preyóusually small insects. In search of prey, they run quickly waving their forelegs before them. Indoors, they can be observed on walls and ceilings, but drop to the floor to seek cover when disturbed

Once indoors, sac spiders may build retreats in the upper corners and the ceiling-wall junctions of rooms and rest there during the day. In basements and crawl spaces, spiders are found where joists and band boards meet the subflorring.

Experts believe sac spiders cause more bites than any other type of spider and their bites are often misdiagnosed as brown recluse spider bites.

The venom of sac spiders contains a cytotoxin, which means it kills cells, like the venom of a brown recluse. Unlike brown recluse bites which can take 2-3 months to heal, most sac spider bites heal much more quickly, although the reaction will vary greatly from individual to individual. Typical symptoms of a sac spider bite include a stinging sensation followed by redness and mild swelling. In a few cases, the bite may blister and break, leaving a sore that can take several weeks to heal. Sometimes the person will feel mildly ill.

During the day, sac spiders may be inside their sacs so vacuuming is an excellent method of control. Remove and discard vacuum cleaner bags to prevent reinfestation. To help reduce numbers entering a structure, exclude by screening vents, caulking around utility entrances and door/window frames.

(Source: National Pest Management Association, et. al.)