The Black-Footed Yellow Sac Spider (Cheiracanthium genus) is venomous, meaning it injects toxins through a bite, which is distinct from being poisonous (toxic if ingested). Although the spider is venomous, its bite is generally not considered medically significant for a healthy person. The effects are usually localized and temporary, causing far less concern than bites from species like the Black Widow or Brown Recluse.
Identifying the Black-Footed Yellow Sac Spider
These spiders are small, typically measuring 5 to 10 millimeters in body length. They are recognizable by their pale coloration, ranging from light yellow to cream or tan. The defining characteristic is the dark brown or black coloration on the tips of their legs (tarsi), chelicerae (jaws), and palps.
The two most common species are Cheiracanthium inclusum (native to the Americas, found outdoors) and Cheiracanthium mildei (introduced European species, often seen indoors). This spider is a nocturnal hunter, unlike web-building species. It rests during the day inside a silken sac or “retreat,” which is not used to catch prey. These small, tubular sacs are often found tucked into corners or under furniture indoors.
Understanding the Venom and Medical Significance
The venom of Cheiracanthium species is a complex mixture containing cytotoxic and potentially neurotoxic substances. Cytotoxins damage cells and tissues around the bite site, while neurotoxins affect the nervous system. The venom contains enzymes, such as phospholipase A2, which break down cell membranes and contribute to the localized reaction.
The risk to humans is low because the amount of venom injected is very small, and bites are almost always defensive. Historically, the spider was misdiagnosed as a cause of severe necrotic wounds, often confused with the Brown Recluse. Current research has largely exonerated the Cheiracanthium genus from causing widespread tissue damage. Although the bite of C. inclusum is sometimes reported to be slightly more destructive than C. mildei, both are classified as low-risk.
Symptoms and Care Following a Bite
A bite typically begins with a sharp, immediate sting, comparable to a bee or wasp sting. This initial pain is quickly followed by localized symptoms, including erythema (redness), mild edema (swelling), a burning sensation, and pruritus (itching) at the site. These localized reactions usually resolve completely within seven to ten days.
In rare instances, a bite may result in a small, persistent sore, blister, or minor ulceration. This localized tissue damage is far less severe than the extensive necrosis associated with a Brown Recluse bite, and it typically heals without a significant scar. Occasionally, individuals may experience mild systemic reactions, such as low-grade fever, general malaise, muscle cramps, or nausea.
Immediate first aid involves gently washing the bite area with soap and water to prevent secondary bacterial infection. Applying a cold compress or ice pack helps reduce swelling and alleviate pain. Over-the-counter pain relievers (acetaminophen or ibuprofen) can be used for discomfort, and oral antihistamines may help manage itching. Seek medical attention if the wound shows signs of infection (spreading redness or pus), if pain or swelling worsens significantly, or if systemic symptoms like a fever develop.