Symptoms of a Black Widow Bite on a Dog

Black widow spiders, easily identified by their large, black abdomen featuring a red hourglass shape, are commonly found outdoors near buildings, in sheds and garages or around woodpiles. The venom from a female black widow bite is a serious neurotoxin that can be fatal if it affects the respiratory organs. Black widow bites in dogs are treatable, and if identified relatively quickly, leave no lasting effects.

  1. Initial Symptoms

    • When first bitten, a dog may not notice, or will feel a sharp, burning pain at the bite location. The venom and pain will spread to the lymph nodes nearest the bite. The pain will reach maximum intensity one to three hours after the bite occurs, and may continue for up to 48 hours, either continuously or intermittently. Swelling and nausea may occur. The dog may show increased activity due to muscle discomfort in the first 10 to 20 hours after the bite occurs.

    Muscle Involvement

    • The venom from a black widow spider bite affects the muscles and nerves, which may cause symptoms such as muscle tremors and spasms; restlessness; rigid muscles, particularly in the abdominal area; and weakness of the muscles. The location of the bite, amount of venom injected and your dog's sensitivity to the venom will affect the number and severity of symptoms.

    Other Symptoms and Treatment

    • Eventually, your dog may experience rapid, shallow or labored breathing. Other symptoms include seizures, increased heart rate and paralysis. If you suspect your dog has been bitten by a black widow spider, contact your veterinarian immediately. Depending on the severity of the bite and your dog's reaction to the venom, your vet may want you to administer an antihistamine and an ice pack at home, or have you bring it in for an I.V. and medication to relax the muscles and aid breathing. Antivenin is available, but prohibitively expensive and typically only available to humans. The best bet is to watch pets closely when outside and keep sheds and garages clear of spider webs to prevent bites altogether.