Identify a Yellow Sac Spider

Despite their name, yellow sac spiders (Cheiracanthium inclusum) aren’t always yellow. They can be yellowish-green or even tan to light brown. These spiders are native to Europe, but were introduced to the United States via storage containers in the 1940s.

Steps

  1. Know what a yellow sac spider is. Here are some key characteristics.
    • Physical features: With an orange-brown stripe on top of the abdomen, 1/4" to 3/8” (6.3 to 9.5 mm) long
    • Venomous: Yes
    • Lives in: primarily in the Pacific Northwest United States and Southwestern Canada
    • Eats: These spiders are nocturnal and hunt actively during the night. They prey on spiders (sometimes spiders larger than themselves), insects and their own eggs.

Identifying a Yellow Sac Spider

There is little difference between male and female yellow sac spiders. The male is usually more slender and may have a slightly larger leg span than the female.

  1. Look at the legs. The first pair of legs is longer than the 4th pair of legs.
  2. Observe the eyes. The 8 eyes of the yellow sac spider are similar in size and they are arranged in 2 horizontal rows.
  3. Examine the areas in your home where the wall meets the ceiling. These spiders often make their sacs in the juncture of a wall and ceiling and hide in the sac during the daytime. If you disturb the sac, the spider will drop to the floor.
  4. Notice their feet, which are black (they are actually covered with tiny black hairs). If your walls and ceilings are light in color, you will easily notice the black feet.

Recognizing Yellow Sac Spider Habitats

This spider creates a sac instead of a web. It prefers to live and hunt outdoors, but when the weather starts turning colder, it move indoors, where it will construct its sac in a corner, usually near the ceiling.

  1. Look for yellow sac spiders in other places like:
    • Garden sheds
    • Garages
    • House foundations
    • Behind picture frames
    • Window sills
    • Baseboards

Treating a Bite

The fangs of yellow sac spiders are powerful and can penetrate human skin. The mild venom produces neurotoxic effects and the bite itself can be quite painful.

  1. Notice if you or the person bitten experiences redness, itching and swelling at the bite area. Remember that all these symptoms disappear within 72 hours though, so quick identification is important.
  2. Once you’ve identified the bite to be from a yellow sac spider, call emergency services as soon as possible.

Tips

  • Because yellow sac spiders hunt for their prey at night, it is a good idea to keep your bed away from walls to lessen the likelihood of getting bitten while you sleep.
  • Most people get bitten by yellow sac spiders when they are gardening or doing other kinds of outdoor activities.
  • You can limit the number of yellow sac spiders that get into your home by installing tight fitting screens on your doors and windows. It also helps to seal all gaps, cracks and crevices where the spider might gain entry.
  • Yellow sac spiders typically live for one to three years, and are preyed on by spider wasps, birds and lizards.

Warnings

  • The symptoms from a bite of a yellow sac spider mimic the symptoms from a bite of a brown recluse spider. If at all possible, capture the spider that bit you so that it can be positively identified. That way, you can get the appropriate medical attention.

Related Articles

Sources and Citations

  • http://www.insectidentification.org/insect-description.asp?identification=Yellow-Sac-Spider
  • Lorus and Margery Milne, Audubon Society Field Guide to North American Insects & Spiders, (New York, NY: Alfred A. Knopf, Inc. 1980)
  • Ken Preston-Mafham, Spiders, The new compact study guide and identifier, (Edison, NJ: Chartwell Books, 1998)
  • Arthur V. Evans, National wildlife Federation Field Guide to Insects and Spiders, (New York, NY: Sterling Publishing Company, 2008)

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