Yellow Sac Spider Bite Turns Woman's Finger Purple and Porcelain White

A woman in Chicago was left with a swollen finger that turned purple and porcelain white after she was bitten by a yellow sac spider. The 53-year-old was seen at a dermatology clinic around 36 hours after the spider bite, when the fifth finger on her right hand became discolored and painful.

Yellow sac spiders are widely distributed across the U.S.. They are found in gardens during warmer seasons, and head indoors when it gets colder in the fall. They are active hunters, so they seek out prey rather than building a web to trap it. Yellow sac spiders can be identified by their yellow bodies and brown fangs. They are small, measuring less than a centimeter (less than half an inch) in length.

There are two types of yellow sac spider in the U.S.—Cheiracanthium mildei and Cheiracanthium inclusum. The former was introduced from Europe in the 1940s, while C. inclusum is a native species.

Yellow sac spiders are known to bite humans. Michigan State University said these spiders account for more human bites in the U.S. than any other species. It said they will "readily bite" and "have been observed crawling across the human skin surface and biting without provocation."

In a case report of a yellow sac spider bite published in the New England Journal of Medicine (NEJM), Adam S. Cifu and Sarah L. Stein, from the University of Chicago, documented a case where a woman had been bitten and managed to bring the spider with her to the clinic. She was examined and her finger was found to be red with a "dusky center." She was treated with painkillers and given an ointment, but the following day the discoloration had worsened and her finger had swollen and was "exquisitely tender." Six days later, the swelling had gone but the skin had turned purple and porcelain white.

yellow sac spider bite
The woman's finger turned red, purple and porcelain white over the course of a week after first being bitten. The New England Journal of Medicine ©2021

Stein told Newsweek she very rarely treats yellow sac spider bites. "Patients not uncommonly come in with an inflamed solitary lesion that they attribute to a 'spider bite,' but they don't have the spider and haven't seen a spider," she said. "These lesions are more often a localized abscess due to a common bacterial infection."

The reaction, Stein said, was typical for a yellow sac spider. She said if people think they have been bitten by a yellow sac spider then anti-inflammatory and pain control medicines are helpful. She also said to protect the site with petrolatum ointment and a bandage.

The woman was completely healed two weeks after she was first bitten. "The spiders typically bite persons who are sleeping or dressing, with the bite causing local pain, redness, and swelling, usually without progression to necrosis, as occurred in this case," the case report concluded.

yellow sac spider
Stock photo of a yellow sac spider, Cheiracanthium inclusum. A woman was treated in a Chicago hospital after getting bitten by one of these spiders. Getty Images