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A source for information on spiders

Yellow Sac Spider Cheiracanthium inclusum

Measuring ten millimeters in body length, yellow sac spiders are relatively small. As their name implies, these arachnids are pale yellow in color, although green, tan, straw and light brown specimens also exist. Upon close inspection, yellow sac spiders have dark mouthparts, as well as a band running laterally down the abdomen. The front legs of the yellow sac spider are longer than the other three pairs. Yellow sac spiders are often confused for other species and are easy to overlook.

In the daytime, yellow sac spiders are found inside their flattened, silk tubes. In warm seasons, these spiders tend to reside in gardens, leaf piles, woodpiles, and timber. In fall, they migrate indoors and can be seen crawling up and down walls, as well as across ceilings and vertical surfaces. Yellow sac spider populations increase significantly in fall, leading to indoor infestations.

Yellow sac spiders hunt for prey at night. These arachnids move swiftly, wielding their front legs before them. They consume small insects and arthropods, as well as other spiders. Some yellow sac spiders have been known to feed on spiders much larger than themselves and others consume their own eggs.


About 1/4-inch in length.


Pale yellowish-green.


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.

Contrary to popular opinion, it is nearly impossible to determine precisely what type of spider has bitten someone, when no spider has been found. Even though brown recluse bites are quite rare these shy spiders are often blamed for bites. 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.

Yellow Sac Spider

Sac spiders belong to the genus Cheiracanthium and the family Clubionidae. They are quite small and easy to overlook—about 1/4 - 3/8 inch long, with no conspicuous markings. The front legs are longer than the other three pairs. Sac spiders are quite pale. A common house species, the yellow sac spider is pale greenish, tan or straw colored. Other sac spiders are light brown.

Sac spiders typically have darker mouthparts and a faint dark stripe running lengthwise down the abdomen.

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 prey—usually 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.

Sac spiders construct a silken tube or sac in a protected area, such as within a leaf, under landscape timbers or logs, or at the junction of a wall and ceiling, and they use this sac as their daytime retreat. This is how the sac spider gets its name. These spiders do not build webs.

After mating, females lay 30 to 48 eggs and cover them in a thin coat of loosely spun silk. The small, white, paper-like sacs are often found in easily overlooked locations, along ceilings and corners, or behind pictures and shelves. The female may guard these egg sacs and may produce several egg masses during her lifetime.

Inspect for sac spiders by looking for sacs in upper corners of rooms, ceilings, behind pictures, on window molding, blinds or curtains. During the day, sac spiders may be inside these sacs so vacuuming is an excellent method of control. Remove and discard vacuum cleaner bags to prevent reinfestation.


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.

"Riley Pest Management is a small company with a big heart that will go the extra mile to take care of an issue for you no matter when it happens. They have proven to be a very good friend to non-profits."

-- Duggan Cooley, former CEO- RCS

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