Spiders are all around us. At least 35,000 species have been recognized with new ones being discovered all the time. Some experts believe the true number of spider species is close to 100,000.
Approximately 20,000 species of spiders are found in the United States. Luckily, only about 50 of these species have fangs that can penetrate human or animal skin. All spiders (except for two families) are poisonous, but not all possess biting mouth parts able to deliver the venom and in others the venom is very weak.
In North America, the two spiders capable of inflicting bites for which patients most commonly seek medical treatment are the black widow (five species of lactro deitus found in the U.S.) and the brown recluse (loxosceles species). The brown recluse spider is found in the southern half of the U.S. These spiders are notorious for the local tissue damage resulting from their bites. The brown recluse can be distinguished by the violin-shaped marking on their backs with the neck of the violin pointing to their abdomen.
Adult female black widows have a reddish-orange hourglass on the underside of their abdomen.
Recluse bites are known for potent venom with a prolonged ulcerative effect. The poison injected is rich in digestive enzymes that produce a skin ulcer that can continue to grow long after the initial bite. The lesion can be active for months and be disfiguring and become secondarily infected. Any suspicious lesions should be examined immediately by your veterinarian.
Occasionally, other spiders are involved in bites, but most often other causes are the culprits and spiders are blamed. Other things that should be considered are abscesses, other anthropod bites (bees, wasps, hornets), allergies, tumors, cat fight wounds and bad teeth.
Find out what spiders live in your area. If you see a spider bite your pet, capture it, if possible, for identification. Keep the closest emergency veterinary hospital and poison control center phone numbers handy. Contact them at the first sign of trouble.