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Spider Bite

Bite from a spider seen on the skin.
Onset of bite symptoms (redness, pain, swelling) and a spider is seen in close proximity.

General Information

There are over 20,000 species of spiders in the world.
In the United States, there are two species that cause bites in humans of medical importance: the black widow (Lactrodectus) and the brown recluse (Loxoscele
If you decide you need to see your doctor, bring the spider along in a jar for identification (brown recluse spiders are especially hard to identify)

Black Widow Spider Bite

The black widow is shiny and black, with long legs (total width 1 inch). A red (or orange) hourglass-shaped marking may be on its underside (not present in all Lactrodectus species)
Black widow spiders are found throughout North America, except in Alaska and the far North.
Causes immediate local mild pain, swelling, and occasionally 2 fang marks. Severe muscle cramps are present by 1 to 6 hours, and last 24 to 48 hours. Rarely causes death (exception: bitten by several spiders or small child is bitten).
Note: many are dry bites because the fangs are small.
FIRST AID for Black Widow Spider Bites: Apply an ice cube or ice pack to the bite for 20 minutes to reduce the spread of the venom (no tourniquet).

Brown Recluse Spider Bite

Also known as the "violin" or "fiddleback" spider.
Is a brown spider with long legs (total width 1/2 inch). There is a dark violin-shaped marking on top of its head (not present in all Loxosceles species).
It can be found in the southern, southwestern, and midwestern United States.
Causes local pain and delayed blister formation in 4 to 8 hours. The center of the bite becomes bluish and depressed (crater-like) over 2 to 3 days. A deep necrotic ulcer may develop. Skin damage may require skin grafting in 10% of cases.
Generalized symptoms such as fever, vomiting, and muscle aches can occur (but no life-threatening symptoms).

Non-Dangerous Spider Bites

More than 50 spiders in the U.S. have venom and can cause local, non-serious reactions.
The bites are painful and mildly swollen for 1 or 2 days (much like a bee sting).
Most single, unexplained, tender bites that occur during the night are due to spiders.