In the continental United States and Canada only the bites of brown recluse and black widow spiders inject venom that can cause serious problems. However, any spider bite can cause significant swelling.
Often the brown recluse bite is at first painless or causes only a brief stinging. Several hours later pain begins around the site and can become severe. The involved area often has a “red, white, and blue” appearance: a wide area of reddened skin, within which is a smaller patch of white-appearing skin, and finally a central bluish discoloration around the fang marks. The central (blue) area usually forms an ulcer that may take weeks or months to heal and occasionally requires skin grafting. This procedure is generally done about two months after the bite because the graft may slough off if applied to the poisoned area too early. Other possible symptoms of brown recluse bites include fever, skin rash, nausea or vomiting, joint pain, and bloody urine.
There is no specific treatment or antidote for brown recluse bites. Many treatments have been tried and found to be ineffective. Cleanse and elevate the wound. Antibiotics are occasionally prescribed, and a tetanus booster is given if needed. In general the best approach is a combination of effective pain relief and keeping the bite site clean and dry to prevent secondary infection.
Brown recluse spiders prefer warm, dry, and abandoned locations – for example, vacant buildings, woodpiles or sheds, or seldom-used closets. The spider is brown with a violin-shaped marking on its back. Active primarily at night, they usually bite when trapped in clothing or shoes. Be careful when delving into closets and other spaces that have been undisturbed, and shakeout clothes and shoes that have been stored awhile or that are kept in areas where brown recluse spiders have been seen.
A black widow bite is generally unnoticed at first but then becomes painful – often severely so – within 15 minutes to 4 hours. Pain will usually reach a peak in 2 or 3hours, but it can last up to 48 hours. Associated muscle spasm, which may be very severe, contributes to the pain. Usually only two tiny red spots are visible at the bite site, or no local reaction may be seen at all.
The primary goal of treatment for a black widow bite is to relieve pain and muscle spasm. An antivenin is available, but it is generally reserved for severe cases, which are more commonly seen in young children.
The black widow is a shy, coal black spider with a red or yellow hourglass marking on the underside of the abdomen. Only the female spider bites. She builds a chaotic, irregular-shaped web that is easy to recognize when compared to the highly symmetrical webs of other spiders. The black widow is found throughout the United States, preferring warm, dry environments, both indoors and out.
These spiders attack only when handled roughly. Their bite can be painless or can cause a deep, throbbing discomfort that generally stops after about an hour. The only treatment needed is elevation and possibly a pain reliever, although most of the discomfort usually subsides before the medication takes effect.