Black Widow Spider Bites on Dogs

Black Widow Spider Bites on Dogs

Black widow spiders are a venomous spider that is common throughout eastern North America, found mainly in the southern part of this geographic range. These spiders are usually found outdoors or in garages and sheds, frequently near buildings. The dangerous females are easily recognized by their bulbous black abdomen with a bright red hourglass shape on the underside. The juveniles and males very rarely ever bite.

Death can occur from a black widow bite when the muscles and nerves associated with respiration become damaged. Dogs that receive prompt veterinary care tend to do well after a black widow bite.

Signs & Symptoms of Black Widow Spider Bites on Dogs

The bite may initially go unnoticed by your dog, or it could cause a sharp, burning pain. Immediately after bite, pain spreads to regional lymph nodes nearest the bite site. Initially, there is little to no swelling at the site of the bite. 1 to 3 hours after the bite, pain reaches maximum intensity; after which pain may be continuous or intermittent, sometimes lasting up to 48 hours. Your dog may show increased activity for the first 10 to 20 hours after the bite, after which paralysis may set in.

Symptoms of a black widow spider bite include:

  • Numbness surrounding the bite site
  • Restlessness
  • Muscle pain
  • Muscle rigidity, particularly the abdominal muscles 
  • Seizures
  • Increased heart rate
  • Labored breathing, usually rapid and shallow
  • Weakness of the limbs
  • Paralysis


Variety in the number and severity of the symptoms may occur due to the location of the bite, the amount of venom injected, and your dog’s individual sensitivity to the venom.

Causes of Black Widow Spider Bites on Dogs

The toxin found in the venom of the black widow spider is a protein called α-latrotoxin, which acts on the nerve endings, causing gradual pain and involuntary muscle contractions.

Black widow spiders belong to the genus Latrodectus. There are a number of other species in the genus, all of which have potent neurotoxic venom. Black widow spiders (Latrodectus mactans) just happen to be the most widespread and most likely to come in contact with people and their dogs.

Treatment for Black Widow Spider Bites on Dogs

If you suspect your dog has been bitten by a black widow spider, contact your veterinarian IMMEDIATELY.  They may recommend administering Benadryl or an ice pack at home to prevent inflammation. They will likely not be able to determine the severity of the bite in a dog without seeing your dog, so a visit to the veterinarian is usually recommended. There, they will likely treat your dog for the symptoms it is displaying.

An antivenin is available, but is usually not given to dogs because it is extremely expensive. Veterinarians do not typically keep antivenin at their clinics and would likely have to retrieve it from a human hospital.

Prevention of Black Widow Spider Bites on Dogs

The best way to prevent a black widow spider bite is to limit your dog’s exposure to the spider. If you know that you live within the black widow’s geographic distribution, or if you have seen one in your area before, keep an eye on your dog when it is outside, if possible. Exclusion may also be possible by sealing storage boxes tight and keeping sheds and attics clean and free of spider webs.

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