Of the two venomous spiders in the United States that pose a potentially serious threat to humans, one species is rare in New York, and the other is not native to the state. More common in the state is a less dangerous, yet still venomous, spider that is sometimes confused with the more harmful species.

Wolf Spider
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The wolf spider is sometimes mistaken for a brown recluse spider.

Black Widow

The female black widow spider is about 1 1/2 inches long when its legs are fully extended, and it is glossy black. The underside of its abdomen is usually marked with a distinctive bright-red hourglass shape. The male is much smaller and typically has white or yellow stripes on the sides of its abdomen.

The female black widow builds a tangled web in a secluded area, such as under a woodpile or low-growing foliage, on a fence or stone wall, or inside a garden shed or other outbuilding. It rarely leaves its web, where it stands guard over its egg sacs. When the spider or its eggs are threatened, it may bite.

The venom from the bite of a female black widow contains a potent neurotoxin that can cause significant reactions, including severe pain, cramping, nausea, shortness of breath and high blood pressure. Healthy adults usually recover from the bite's effects in a few days, but the bite may be fatal in children, the elderly and other vulnerable individuals.

Black widow spiders prefer warm climates so are not common in New York. Their range, however, extends as far north as southern Maine. So these potentially dangerous spiders could make an appearance in New York gardens, yards and buildings.

Brown Recluse

The brown recluse is a pale- or medium-brown spider with a body length of about 2/5 inch and 3/4-inch-long legs. It usually has a darker brown, fiddle-shaped marking on its back, extending from the back of its head toward the rear of its body.

The brown recluse, as its name implies, is a shy spider that usually stays away from human activity. It hunts at night; during the day, it hides under rocks, in woodpiles and in other secluded locations.

The bite of the brown recluse is often not painful at first, but pain may develop later, along with a blister at the site of the bite. Over time, the bite area may become red, swollen and hot, and in severe cases, an ulcerated sore may develop around the area.

Even more so than the black widow, the brown recluse prefers warm climates, and the species does not occur naturally in New York. Introduced specimens may be able to survive for a time in the state, though. Spiders thought to be brown recluses are more likely to be misidentified specimens of other species, such as wolf spiders, grass spiders or sac spiders.

Sac Spiders

Spider bites in New York blamed on brown recluses are more probable to be bites attributable to the much more common yellow sac spiders. These spiders are pale yellow, with a body length of less than 1/2 inch; like the brown recluse, they hunt at night and hide during the day. In the garden, their hiding places are likely to be under rocks or inside rolled-up leaves, in which they build silken tubes in which to hide.

A sac spider bite is usually painful initially, and in some individuals it may cause cramping, nausea and other symptoms similar to those of a black widow bite. Eventually, an open sore or tissue death similar to, but less severe than, that caused by a brown recluse bite may occur at the site of the bite. Usually, though, the bite doesn't cause serious harm.

First Aid and Prevention

If you think you were bitten by a black widow spider, then get medical attention right away. Treatment usually involves using ice to control swelling and medication to treat pain, but symptoms usually resolve on their own. In extreme cases, antivenin may be administered.

If you think you were bitten by a brown recluse or sac spider, use ice and a pain reliever to treat the symptoms. Seek medical attention if an open sore or any sign of infection develops, or if you experience symptoms that involve your entire body rather than just the site of the bite.

Avoid bites from potentially dangerous spiders by wearing gloves, a long-sleeved shirt and long pants while working in a garden or elsewhere outdoors, particularly when working in the secluded locations where the spiders often hide.