Dangerous Spider Bites in Dogs

In the United States, there are only three poisonous spiders, the black or brown widow and the brown recluse.  The bites of both spiders can be life threatening to your dog.

The black widow is known to most people.  Another related spider is the brown widow, which also has the characteristic hourglass on the bottom of the abdomen  The spider may bite and not inject venom, or may inject a full load of venom. The venom is a potent neurotoxin, opening channels at the presynaptic nerve terminal and causing massive release of acetylcholine and norepinephrine, both of which can cause sustained muscular spasms and paralysis. It causes one or more of the following symptoms:  paralysis, muscle tremors and cramping, abdominal rigidity, severe muscle pain, manifested by howling, whining, and other loud cries, trouble breathing, excessive drooling, restlessness, increased blood pressure and heart rate, inability to stand, vomiting, diarrhea, and death.  This is an extremely painful event for the dog.  Immediate treatment is necessary.

Older dogs and young dogs are more at risk of dying.  Dogs with high blood pressure or heart problems also die at a higher rate than healthy dogs.

Diagnosis of the bite is difficult because so many other things can cause each of these symptoms in isolation.  The veterinarian will take a blood sample and urinalysis, and perhaps a stool sample.  If the dog has vomited up a spider, take it with you to the veterinarian for identification.  The veterinarian will also look for a bite site, localized swelling and fang marks.

This situation is very serious.  The dog will be hospitalized and the symptoms treated.  Intravenous fluids, anti-venom, anti-spasmodics, and pain medicine will be administered.  The dog will need to be monitored to make sure that these medications are helping.  Once he leaves the hospital, the veterinarian will examine the wound site once a week until it is healed.  Weakness, fatigue, and insomnia may persist for months, and the dog may die from the bite.

Unfortunately, it is difficult to prevent this problem.  Black and brown widows like to hide in dark corners and under things.  Eliminating the spiders will help protect your dog.

The brown recluse is also a dangerous spider.  These spiders are reclusive and non-aggressive.  They typically bite when trapped in bedding and a human or dog rolls over on them.  The bite then causes a reaction at the site of the wound where the tissue dies.  This necrotic wound can spread and is very slow to heal, leaving the dog vulnerable to infections.  Occasionally, the wound becomes gangrenous. If the venom happens to be injected into the blood stream it can cause this necrotizing problem in internal organs.  The faster the wound is diagnosed, the better the chance that the damage can be minimized.

The veterinarian will take a through history of the dog from you.  The wound can mimic other types of wounds, so a history is necessary.  Blood analysis, urinalysis, and the presence of venom in the bloodstream will tell the veterinarian that the bite is from a brown recluse.  The test for venom in the bloodstream is not used unless the veterinarian suspects a brown recluse bite.

A mild case of poisoning will be treated with routine wound care.  Severe poisoning may require the excision of the wound site to stop the necrotizing of the site.