Black Widow Spider Poisoning in Dogs

Spiders in the Latrodectus family, also known as widow spiders, come equipped with a potent neurotoxin to debilitate enemies and prey. The spider actually develops multiple types of venom so that it is toxic not only to vertebrates, but also to insects and to crustaceans. Only the mature female of the species ever gets large enough for their bite to pierce the skin of most canines. Black widows are web spinning spiders that make their homes in areas that are dark, warm, and dry. Most varieties can be identified by a distinctive red hourglass on their abdomen, although it may have a more broken or rod-shaped look in certain species. A bite by a widow spider should prompt immediate contact with your veterinarian.

Spiders in the widow family are equipped with a potent neurotoxin that can cause painful cramping, seizures, and possibly death. Contact your veterinarian immediately if your pet is bitten.

The black widow bite is an initially painful bite which tends to leave a raised red area on the skin. The dog may start worrying at or licking the area of the bite. Other symptoms have a delayed onset of 30 minutes to two hours and can include:

• Blood pressure changes
• Cramping
• Death
• Diarrhea
• Drooling
• Drunken gait
• Labored breathing
• Limb weakness
• Loss of coordination
• Muscle rigidity
• Paralysis
• Restlessness
• Seizures
• Severe muscle pain
• Tremors
• Vocalizations
• Vomiting

It is not unusual for the canine to vomit up the spider. If this happens, take the spider with you to the veterinarian. 

Types

There are five species of widow spiders found in the US:

Brown widow spider (Latrodectus geometricus)

Found exclusively in Florida until around 2000 when they began to spread, this spider is brown with an orange hourglass and although their venom is just as potent they deliver less of it in their bite than the black widow relatives. 

Northern widow spider (Latrodectus various)

Common in the northern U.S., its hourglass is not joined and resembles large spots on its abdomen.

Red-legged widow spider (Latrodectus bishop)

This spider is a threatened species of widow found in central and southern Florida. Only their abdomen is black and the red hourglass is replaced with a small red bar.

Southern black widow spider (Latrodectus mactans)

This is the most common widow spider. It is black with the red hourglass pattern on the female’s abdomen. Only mature females are large enough to deliver the venom. It is found mainly in the southeastern United States, although it shares some territory with the western black widow 

Western black widow spider (Latrodectus hesperus

Found in the western U.S., it is very similar to the southern black widow but mainly found in the western regions of the U.S.

The danger in black widow bites lies in the venom. The type of venom that black widows produce is called a protein called a-latrotoxin. These toxins are specialized to target either insects, crustaceans, or vertebrates such as us. The latrotoxin that has developed to target vertebrates is called a-latrotoxin. Once it is absorbed into the blood stream it causes involuntary muscle spasms and severe pain as it targets the nerve endings.

Your veterinarian is likely to start with a history of the symptoms from you and a physical examination paying special attention to the area of the bite if it is known. A complete blood count, biochemistry profile, and urinalysis is likely to be done at this time as well to rule out other disorders with the same symptoms. Laboratory results may show the presence of albumin in the urine, and possible increases in creatine phosphokinase, glucose, and bilirubin. Other toxins and disorders that may initially present with similar symptoms could include macadamia nuts, intervertebral disc disease, or a central nervous system neoplasia. There is no test to detect black widow venom in your pet’s blood so unless the bite is witnessed or found or unless your pet vomits up the spider the diagnosis is likely to be a presumptive diagnosis based on the symptoms after ruling out other disorders and toxins.

In most cases the patient will be hospitalized for black widow venom and supportive treatment will be given to ensure proper hydration and pain management. Muscle relaxants or benzodiazepines will be administered to allow the muscles to stop spasming. These medications need to be consistently monitored to prevent respiratory distress in the patient, and oxygen may be required to help your pet overcome the toxin. Antivenin will be used if it is available to your veterinarian but it is often a prohibitively expensive to have on hand, so they will usually need to get it from a human hospital. There is a small risk of an allergic reaction to the antivenin and should be administered carefully. Due to the severe nature of the toxin and the need for constant monitoring your pet may be at the hospital for several days. Although most animals recover within 48-72 hours, residual weakness, fatigue, and insomnia may continue for several weeks.

Keeping the recuperating patient in a calm and quiet environment and ensuring that food and water are easily available will speed the healing process for your dog. Your veterinarian will likely want to check the site again on a weekly or more basis to ensure that it heals fully. The final prognosis is often uncertain for several days after treatment and the patient should be closely watched for signs of respiratory issues or relapse. Symptoms such as weakness, fatigue, and insomnia may persist for several weeks. If the dog was bitten in the house you will want to inspect the house for further infestation, for your pet’s protection and your own.