The black-footed yellow sac spider (Cheiracanthium inclusum) is common across the Americas. This article provides science-based information on its venom, bite appearance, immediate care, and identification features.
Understanding Their Venom
Black-footed yellow sac spiders are venomous, not poisonous. The distinction lies in how the harmful substance is delivered: venom is injected through a bite or sting, while poison is toxic if ingested or absorbed. The venom of Cheiracanthium inclusum is generally considered mild and not medically significant for most individuals. While it contains cytotoxic properties, which can affect cells and tissues, severe reactions are rare.
The effects of their venom are usually localized to the bite area. While the venom can cause discomfort, serious outcomes are uncommon. Necrotic lesions, or tissue damage, are rare following a bite from this spider. Concerns often stem from misidentification or exaggerated reports, rather than a true threat to human health.
What a Bite Looks Like
A black-footed yellow sac spider bite often results in immediate, moderate pain, similar to a bee or wasp sting. This initial pain may be followed by localized symptoms such as redness, swelling, and itching around the bite site. A small, red bump forms, which can evolve into a blister over the next few hours to a day.
The blister can be filled with clear fluid and may lead to a small open sore if it breaks or is scratched. While a necrotic lesion can occur, this is less common and less severe than those caused by other spiders, such as the brown recluse. Most symptoms resolve within 7 to 10 days, though some discomfort may persist for up to a week.
Immediate Steps After a Bite
If a black-footed yellow sac spider bite occurs, clean the affected area promptly with mild soap and water to help remove any surface venom. Apply a cold compress or ice pack to the bite for about 10 minutes to help reduce pain and swelling. Elevating the affected limb, if possible, also minimizes swelling.
Over-the-counter pain relievers, such as ibuprofen, can manage discomfort and inflammation. Avoid scratching the bite to prevent secondary infections. While most bites heal on their own, medical attention should be sought if symptoms worsen, signs of infection appear, or if an allergic reaction develops, such as difficulty breathing, facial swelling, or dizziness.
How to Identify Them
Black-footed yellow sac spiders (Cheiracanthium inclusum) are small, with females measuring 5-9 millimeters and males 4-8 millimeters in body length. Their coloration ranges from pale yellow to light cream, sometimes with a subtle greenish tinge on the abdomen. A distinguishing feature is the dark brown markings on their palps, chelicerae (jaws), and the tips of their tarsi (feet), which gives them their “black-footed” common name.
These spiders possess eight similarly sized eyes arranged in two horizontal rows. They are active nocturnal hunters, meaning they do not build webs to catch prey but instead seek out insects and other arthropods. During the day, they retreat into small, silken sacs, which they construct in protected areas like corners of walls and ceilings indoors, or under foliage and stones outdoors.