Spiders can be found in nearly every corner of the world, except Antarctica, but the spiders most people worry about are the ones lurking in the corners of their homes, like the brown recluse or black widow. A brown recluse spider has been named as the possible culprit in the recent case of Victoria Franklin, a woman living in Georgia who lost her breast from gangrene after being bit by the arachnid.

According to The World Spider Catalog, there were 41,253 species of spiders identified as of December 16, 2009, but only a few are dangerous to humans. Two of those dangerous spiders can be found in the contiguous United States, and especially in the southern states where Ms. Franklin lives: the brown recluse and the black widow. These spiders prefer a warm environment and dark, dry hiding places where they can be left alone, like closets and woodpiles.

Although a great many people fear spiders (some to the point of phobia, called arachnophobia), the creatures do much good by capturing and eating other insects. Even though all spiders have some amount of venom that varies in potency, the vast majority of spiders are not dangerous to people because their fangs are too short or too fragile to penetrate a person’s skin.

A spider generally bites a person because it has been frightened or disturbed in its hiding place and it is trying to defend itself. In brown recluse most cases, a bite mark from a spider is too small to be seen easily, and often people do not remember being bitten.

According to the California Poison Control System, spider bites typically cause pain, small puncture wounds, redness, swelling, and itching that may last a few days. It is rare for a spider to bite more than once, so if you have multiple bites, you have probably been bit by fleas, bedbugs, ticks, mites, biting flies, or another insect.

The black widow spider bite is serious, but it is rarely lethal. If you see the spider, it has a red hourglass mark on its underside. A bite from a female black widow spider results in slight swelling and faint red marks initially, and then within a few hours intense pain and stiffness set in. Other signs and symptoms include chills, fever, weakness, headache, elevated blood pressure, nausea, vomiting, and severe abdominal pain. Those at greatest risk of developing symptoms are young children, the elderly, and people who have high blood pressure.

In many cases, the spider does not inject venom and no serious symptoms develop. If muscle cramps develop, you should seek medical care for treatment of the symptoms. A black widow spider antivenin is rarely necessary but it is available.