Do Spider Bites Cause Skin Infections?

Can spider bites lead to an infection through a break in your skin? More importantly, can spiders be carriers of human pathogens?

Scientists from the University of California Riverside, have concluded that evidence for spider-caused infection is sparse.

They data-mined publications on spider bites to answer the question once and for all, and found that the mere presence of bacteria on spider fangs or mouthparts does not establish spiders as vectors for these bacteria.

“Although spider bite may be an attractive and tenable causative agent of a bacterial infection, the data show this is highly improbable,” said lead author Richard S. Vetter. “Any implied causative association between skin infections and spider bites should be considered suspect. The medical community should not scapegoat spiders for bacterial infections. When examining reports of thousands of spider bites of many species worldwide, we found almost no mention of infection associated with the arachnid-inflicted injury.”

Misdiagnosed Bacterial Infections

According to Vetter, one important advancement in spider bite diagnosis in recent years is the knowledge that bacterial infections have been commonly misattributed as spider envenomation by both physicians and patients.

The term “‘spider bite’ is used by default as a diagnosis, despite lack of supporting evidence, said Vetter.

“In a study published three years ago, of 182 Southern Californian patients presenting with complaint of spider bite, less than 4 percent had spider envenomations, while about 86 percent had skin infections.”

He notes that the only convincing report of a spider bite leading to infection that his team is aware of is a case involving an Australian golden silk spider, which a very large orbweaver.

Orb-weaver spiders are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields and forests. Their common name is taken from the round shape of this typical web.

Stop Blaming Spiders

“It resulted in colonization by a bacterium rarely found in humans,” he said of the case. “The bite led to a pus-filled lesion that persisted more than two months.”

Vetter recommends that people concerned with skin infections, both the medical community and the general public should stop pointing to spiders as the cause of bacterial infections.

“This medical platitude is not supported by the history of spider bite data and could lead to misdiagnosed patients who then have an overzealous reaction that could, in turn, lead to the unwarranted development of arachnophobia in bite victims, possibly then requiring psychological desensitization to spiders or excessive use of pesticides in living spaces,” he said.

For More Information:

Richard S. Vetter, David L. Swanson, Scott A. Weinstein, Julian White,
Do spiders vector bacteria during bites? The evidence indicates otherwise,”
Toxicon, Volume 93, January 2015, Pages 171-174, dx.doi.org/10.1016/j.toxicon.2014.11.229.

Photo: Peter Harrison