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Yellow sac spiders: Facts and bites

While many spiders exist, the yellow sac spider is one of the more common ones encountered. This creature may be located in your home or business and given that it’s a venomous pest, it warrants your attention. Learn more here about the yellow sac spider’s appearance, lifestyle and most importantly – its bite.

Find out some basics about the yellow sac spider below. And if you’re stressing about yellow sac spiders where you live or work, call Western Exterminator at 800-937-8398 or contact us online to get in touch with a pest expert.


Have you noticed what looks like a yellow sac spider? Contact Western right away!

What is a sac spider?

Sometimes referred to as a “yellow sac spider”, these spiders are often pale yellow in color and have even been known to have a hint or tinge of green. Similar to most spiders, sac spiders prefer to stay away from human contact and typically only find their way indoors by accident. The sac spider is commonly found in homes and is often mistaken for the brown recluse because it is similar in shape, but the sac spider lacks the “fiddle” pattern of the brown recluse. For the most part, sac spiders prefer to feed on a variety of types of spiders along with other garden insects.

A sac spider typically creates a flat silk sac as the place where it passes most of the daytime. This sac may be located in a shielded spot, like where a wall and ceiling meet, or in a leaf. In fact, they do not create webs. Sac spiders are commonly pale. They have eight eyes that are in two rows. Female sac spiders lay 30 to 48 eggs and put silk over them.

Sac spider habitat

Outdoors, sac spiders can be seen in gardens, under vegetation, bark, in rolled leaves, and organic debris. Sac spiders are often shipped in agricultural products such as grapes and can make their way into homes on produce. It is common to see these spiders inside a home during the fall as they begin to seek warmth from the dropping temperatures outdoors. Sac spiders can easily climb slick surfaces and will construct silk, sac-like retreats wherever walls meet other walls or ceilings.

Sac spider behaviors, threats, and dangers

Sac spiders are hunting spiders that use their silk sac only for their retreat or for their egg capsules. They are nocturnal, hunting at night for other insects. The bite of a common sac spider can be misdiagnosed as a brown recluse spider bite. Injuries develop in a similar manner but are much less severe. Although the bite of a yellow sac spider can be painful, it is not medically significant except for allergic individuals. Reactions, such as swelling, slow healing, and ulcerated sores around the bite site, are similar enough to be confusing. If you suspect that you have been bitten by a spider, seek medical attention if symptoms persist or intensify.

Yellow sac spider species

North America has two species – cheiracanthium inclusum and cheiracanthium mildei – that are known as yellow sac spiders (both occur in California). It is believed that C. mildei was introduced from Europe. You will more commonly find C. inclusum outside and C. mildei inside. C. inclusum is not found in the most northern states of the U.S.

C. mildei adult females have bodies that are ¼ to ⅜ inches in length (males are 3/16 to 5/16 inches). This spider can be light green to yellow-white in color and the legs are darker. Its jaws are brown. C. inclusum adult females are 3/16 to ⅜ inches in length and males are ⅛ to 5/16 inches in length. These spiders can be light yellow in color but otherwise resemble C. mildei. The abdomen of C. inclusum and C. mildei has a stripe that’s a bit darker.

For reference, the yellow sac spiders described here are smaller than a quarter in size. However, it is noteworthy that yellow sac spiders are not always yellow in color.

C. mildei and C. inclusum hunt and eat at night. C. mildei can be located at ceiling-wall corners, and you might notice them moving on ceilings and walls in the nighttime. C. inclusum can be found in a garden and can conceal themselves under bark when it’s daytime. C. mildei and C. inclusum can move into buildings or cars during the late summer and early in the fall to spend the winter.

Are yellow sac spiders poisonous?

Yellow sac spiders are venomous. You could get bitten if this creature is caught in your clothes. A C. inclusum spider may bite you if you are outside working in your garden. It’s possible for a yellow sac spider bite to be misidentified as the bite of a brown recluse spider. If you are bitten by a spider, try to catch it in order to have it identified.

Yellow sac spider bite symptoms

The yellow sac spider’s bite can hurt. A paper published in 2006, “Verified bites by yellow sac spiders (genus cheiracanthium) in the United States and Australia: where is the necrosis?”, covered 20 cheiracanthium genus spider bites from the U.S. and Australia and found that in all instances, people experienced pain or discomfort. It lasted for an average length of 1 hour and 45 minutes. One person dealt with a headache and someone else experienced nausea and vomiting.

If you are bitten by a yellow sac spider, you may experience redness, swelling, and burning. Some suggest applying hydrogen peroxide to where you have been bitten and using an ice pack to decrease swelling. But we always recommend checking with a professional for treatment advice. And certainly, if you encounter nausea, vomiting, headache or other types of severe issues, seek medical attention immediately.

How to get rid of yellow sac spiders

If you’re seeking to control yellow sac spiders, get rid of silk sacs – especially ones located where the ceiling meets the wall and at the corners of the ceiling. You can use a vacuum to eliminate the sacs, but bring the bag outdoors when you are finished.

Even though you can try to battle a spider problem yourself, we know that pest issues can get out of hand. If that’s the case, you should turn to a professional. Fretting about yellow sac spiders or other spiders on your property? Reach out to Western Exterminator today to find out how our experts can help!

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Yellow sac spiders in Seattle

The yellow sac spider is a common pest in the Seattle area. Our specialists know how to handle them and any other spider you might encounter.