Spider Bites

Introduction All spiders are poisonous. Luckily, most spiders are unable to penetrate human skin with their fangs (chelicerae), or the quantity of poison is too small to be a threat. About species of spiders (out of 3000) are known to bite humans in the U.S 1. Up to 80% of presumed “spider bites” may actually be due to other causes, including bites of other insects, cellulitis, burns, and vasculitis. To be a definite spider bite, the spider must be observed immediately after the bite and there must be evidence of the bite

Introduction - continued Reactions to spider bites can be local, with potential for necrosis, as well as systemic. A typical local reaction may cause local redness with a tender nodule and last 7-10 days. Necrotic lesions can develop and manifest as 5-15 cm of expanding erythema, followed by blister formation in 15 to 36 hours. Typically, an ulcer forms, with possible sloughing of necrotic material and scarring. In one case series of necrotizing fasciitis in 31 patients, 2 had a brown recluse spider bite as the initial event, although both also had a history of diabetes and peripheral vascular disease 2. 2

Spider types: Widow (Lactordectus) Widow spiders such as the black widow are 3-4 cm in total diameter including the legs. Found in all 48 contiguous states 6, they are shy and live in outhouses, piles of firewood, rock piles, and bales of hay. The typical victim is a rural child who has attempted to catch the spider Picture and caption from UpToDate

Spider Types – Widow (cont.) Lactrodectism is the syndrome of systemic symptoms resulting from spread of the neurotoxin through the blood and lymphatics minutes after the bite the victim experiences discomfort around the area of the bite. Symptoms can include muscle spasms, abdominal pain, hypertension, confusion, mania, anxiety, and thirst. Hands and faces can become swollen and burning or tender. Benzodiazepine monotherapy is an effective treatment, and even without this patients usually recover in 24 hours 3. The mortality rate is roughly 5%. While there is an antivenin, this itself can cause deaths, and the risk of allergic reaction is high

Spider Types: Brown (Loxosceles) Brown recluse spider bites occur more commonly than black widow bites 3. Brown recluses are found most often west of North Carolina, in the Midwest and South central region of the country 6. They are often dull yellow, occasionally brown or black, and the entire spider the size of a quarter 3. The capacity of the venom of this spider to cause necrosis is due to sphingomyelinase-D 3. Because bites are antigenic, subsequent bites are not as bad as the first Picture from “brown recluse”

Spider Types: Brown (cont.) In the rare cases (about 5%) in which brown recluse spider bites cause any problem, the bite produces a painful, sinking blue macule with surrounding erythema 3. Bites are typically under clothing. Systemic effects, or loxoscelism, can include fever, vomiting, malaise, mild leukocytosis, and sparse black urine due to hemolysis. Care is supportive and symptoms are typically self-limited, though death may rarely result from complications of hemolysis. 3

Spider Types: Tarantula (Orthognatha) These spiders are famous for their large size, with bodies 3-4 cm in diameter and total size up to 25 cm. However, they are not aggressive, rarely bite, and are increasingly being kept as pets. While their bite can produce a throbbing pain for a few hours, no necrosis or systemic symptoms occur. However, their venomous body hairs can induce anaphylactic reactions. Picture from “tarantula”

Spider Type: Spiderman Tobey Maguire was bitten by a genetically engineered spider in 2002 which gave him super powers and millions of dollars. However, these side effects are unfortunately rare. Picture from

Treatment Treatment of spider bites includes washing with soap and water and tetanus prophylaxis. A Medline search did not reveal any great data for treatment, but UpToDate suggests antibiotics (e.g. erythromycin 500 mg q6) only if there are signs of infection such as erythema or suppuration. If necrosis develops, systemic corticosteroids may be given. Dapsone may also limit necrosis. Wound care with debridement is recommended if ulceration occurs. Pain control can be achieved with acetaminophen, opioids, and calcium gluconate for muscle spasms.

References 1.Wong RC, Hughes SE, Voorhees JJ. Spider bites. Arch Dermatol Jan;123(1): Majeski J. Necrotizing fasciitis developing from a brown recluse spider bite. Am Surg Feb;67(2): Anderson PC. Spider bites in the United States. Dermatol Clin Apr;15(2): Isbister GK, White J. Clinical consequences of spider bites: recent advances in our understanding. Toxicon Apr;43(5): Jelinek GA. Widow spider envenomation (lactrodectism): a worldwide problem. Wilderness Environ Med Nov;8(4): Kemp ED. Bites and stings of the arthropod kind. Treating reactions that can range from annoying to menacing. Postgrad Med Jun;103(6):88-90, 93-6, 102 passim. 7.UpToDate, online version 13.1, 2005