Spider Bites in Pets
by Kevin Fitzgerald, Ph.D., D.V.M.
Of Animal Planet's Emergency Vets
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.
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