There are more than 100,000 different kinds of spiders in the world and about 2.2 million spiders per acre of grassy field. Not a comforting thought if you suffer from arachnophobia (fear of spiders).

The good news is that out of all the different types of spiders, only two in the United States are considered venomous to humans, and even these spiders rarely bother humans unless they are provoked. They are the Black Widow and the Brown Recluse.

The Poison Control Center receives many calls about spider bites year-round.

If you think you or your child has been bitten by a venomous spider, immediately contact the Poison Control Center at 1-800-222-1222 or your doctor.

Black widow

The female Black Widow spider can inflict a toxic bite on humans. She is given her name because of her color and because she devours her male partners, making herself a "widow."

This shiny, black spider is 8-10 millimeters long and has a distinct reddish hourglass-shaped mark on her abdomen. The Black Widow's bite feels like a pin prick. Two small red spots may appear on the skin where the bite occurred. The venom contains a toxin that affects the nervous system.

Symptoms

Within 30 minutes to two hours after the bite, symptoms will occur. Symptoms can include:

• Severe back pain
• Muscle cramps
• A rigid sensation in the abdomen
• Nausea

• Vomiting
• Sweating
• Restlessness
• Elevated blood pressure

The maximum effect usually occurs three hours after the bite, but in severe cases, pain may persist for several days. Fatalities are extremely rare.

Treatment

Most people recover completely as long as they obtain treatment, which includes pain relievers, fluids, tetanus shots and other measures. Antivenom is available and highly effective, but is used only for high-risk cases and multiple bites.

Brown recluse 

Although this spider is more prevalent on the East Coast than the Black Widow, no Brown Recluse spiders are thought to live in Pennsylvania or more northern states.

The Brown Recluse has a brownish tint and likes to hide in dark, secluded places. This spider is about the size of a Black Widow in body length (8-10 millimeters), but has a leg span of 20-30 millimeters (1 inch) and has a violin-shaped marking on its back.

The bite of a Brown Recluse tends to cause serious effects. The venom contains chemicals that cause severe tissue damage.

Symptoms

A bite by a Brown Recluse is initially painless. After a few hours, itching, tingling, redness, and pain develop at the site and a lesion begins to form. This lesion resembles several red rings encircling white areas, radiating from a white central blister. It is often referred to as a "bull's eye" or "target" lesion. This lesion is usually fully evident within eight hours of the bite and is helpful in diagnosing a Brown Recluse bite.

If untreated, the lesion may blister, ulcerate and eventually result in dead tissue. Skin grafting procedures may be required to repair the damage.

In addition to extensive local tissue damage; an untreated Brown Recluse bite may eventually affect major organ systems. If this occurs, your child's symptoms will be evident within 12-24 hours of the bite and may include fever, chills, headache and gastrointestinal upset. Later, bleeding disorders or kidney failure may result.

Treatment

Brown Recluse bites require prompt medical attention. Treatment may include wound care, antibiotics and other symptomatic care. Healing of lesions can take weeks or months, depending on the severity of the wound. Currently, there is no available antidote.

Other spiders

Although Black Widow and Brown Recluse spiders may be threatening, most spiders that you and your children are likely to encounter are essentially harmless, especially if you leave them alone. They will bite if provoked, but their bites are not considered medically dangerous.

You can expect to see a reaction similar to that of a bee sting, including redness, pain and swelling at the site. Sometimes other symptoms, including headache, nausea and vomiting, may occur. Good cleaning techniques and proper first aid should be practiced for all spider bites.

If your child is bitten by an unknown spider:

• Save the spider for identification purposes, even if the spider is dead.
• Clean the skin near the bite thoroughly with soap and water.
• Check with your child's doctor about a tetanus booster.
• Apply topical antibiotic ointment to prevent infection.
• Hydrocortisone cream may be used to reduce inflammation.
• Consider using antihistamines for severe swelling.
• Analgesics may be taken to control pain.
• Contact your child's physician if the area becomes infected.

Generally, spiders are found in dark corners, but can be found just about anywhere. Make sure your child wears gloves, long pants and long-sleeved garments if handling wood for the fireplace, cleaning out the attic or garage, or working in the garden or other "spidery" places. Your child should wear shoes at all times when outdoors.