Many people are apprehensive about brown recluse spiders, especially regarding their presence in Illinois. This article provides accurate information on where they live, how to identify them, and what to know about their bites.
Brown Recluse Presence in Illinois
The brown recluse spider (Loxosceles reclusa) is found in Illinois, primarily in the southern two-thirds of the state. Their presence diminishes northward. Occasional sightings in northern Illinois, including the Chicago area, are generally due to human transport, not established breeding populations. These spiders can “hitchhike” on furniture, boxes, and other items. Temperatures below -5 degrees Celsius limit their overwinter survival, explaining their restricted northern distribution.
Identifying a Brown Recluse
Identifying a brown recluse spider involves specific physical characteristics. A recognized feature is a dark, violin-shaped marking on its cephalothorax (the fused head and thorax where legs attach). The “neck” of this violin points towards the abdomen, and its intensity varies, often darker in mature spiders. A more definitive identifier than the violin mark, which can be misinterpreted, is the spider’s eye arrangement. Unlike most spiders with eight eyes, brown recluses have six eyes arranged in three pairs (dyads) forming a semicircle on the front of their cephalothorax.
Brown recluses also have a uniformly colored abdomen, typically light to dark brown, covered in fine hairs, giving it a velvety appearance. Their legs are uniformly colored without stripes, spots, or conspicuous spines, distinguishing them from many other spiders. An adult brown recluse’s body, excluding legs, measures 0.25 to 0.5 inches (0.6 to 1.2 cm) long, roughly the size of a quarter when including its legs.
Commonly Mistaken Spiders
Many common Illinois spiders are mistaken for brown recluses due to similar coloration or appearance. Wolf spiders are large, often hairy, and brown or gray, but lack the violin marking and have eight eyes, with two noticeably larger. Cellar spiders, or “daddy-longlegs,” have long, delicate legs and small bodies; though some are light brown, their markings and body shape differ significantly.
The woodlouse spider, with its reddish-brown front half and gray abdomen, is sometimes confused with the brown recluse, but its distinct, prominent jaws and uniform gray abdomen differentiate it. Common house spiders, small and brown with chevron-like markings, are also often misidentified. These spiders lack the brown recluse’s specific eye arrangement and violin pattern, which are critical for accurate identification.
Understanding Brown Recluse Bites
A brown recluse spider bite is often initially painless. Within hours, the bite site can become red, sensitive, and develop a burning sensation. A blister may form, and the area around the bite might enlarge, sometimes resembling a “bull’s-eye” pattern with a pale center.
While many brown recluse bites result in only mild redness and swelling, similar to a bee sting, some can progress to more serious wounds. In a smaller percentage of cases, tissue death (necrosis) can occur, potentially leading to an open sore that may take weeks or months to heal. Systemic symptoms like fever, chills, nausea, and joint pain are uncommon but can occur, particularly in children or those with compromised health.
If a brown recluse bite is suspected, immediate first aid includes cleaning the bite area with soap and water. Applying a cold compress or ice pack and elevating the affected limb can help reduce swelling and discomfort. Over-the-counter pain relievers and antihistamines may manage pain and itching. Medical attention is advised if the wound shows signs of infection, such as increased pain or drainage, or if the bite area continues to grow and deepen. A doctor may recommend antibiotics or a tetanus booster if needed.