What if a black widow bites my cat (they are sensitive to their venom)?

If you know for sure that a black widow spider has bitten your cat you have to take her to a veterinarian as an emergency i.e. within the next 30 minutes. The bites of black widow (and brown recluse) spiders are toxic to animals. The cat will feel a sharp pain at the site of the bite. Thereafter the following symptoms may occur: the cat develops excitability, chills, laboured breathing and fever.

Black widow spiders can kill cats

Raw image in public domain.

Thereafter seizures and shock may occur followed by early paralysis. The symptoms may be difficult to diagnose because they overlap with other illnesses including certain types of poisonings. The cat’s prognosis may be uncertain, and symptoms of weakness, fatigue and insomnia may persist for many months.

Update 2022: Dr. D Lee Pickett, DVM, has usefully provided an article on the Reading Eagle about how cats are especially sensitive to black widow spider venom. It is the most venomous spider in North America. It is more potent than rattlesnake venom. Only females can poison mammals, however. Their venom is present throughout their body and even in the eggs remarkably.

And the female’s fangs are long enough to penetrate the skin of animals and humans. And the problem here is that domestic cats sometimes play with the spiders which can result in bites. And they might also eat the spider.

Fortunately, black widow spiders don’t bite unless they are provoked, or their webs are disturbed. Below I set out the symptoms and the sad fact that many cats will die which leads to the obvious conclusion that the most important part of treatment is antivenom which should be given up to 24 hours after the bite.

The cat will require intensive hospital care and without treatment the bite is usually fatal. Apparently in one study after 4.8 days, 20/22 cats bitten died.

You can recognise a black widow spider by the fact that they are about an inch long, they have a shiny black or brown body with a red or orange hourglass-shaped mark on the underside of their abdomen. They live around and in houses throughout the US except in Alaska and southern Canada.

They create final-shaped webs. They are named after the fact that the female eats the male after mating which automatically leaves her as a widow.

The following more detailed symptom list is supplied by healthypets.mercola.com. Thank you.

Early marked paralysisMuscle tremors and cramping
Rigid and painful abdomenSeverely painful muscles in the back, chest, and abdomen
Difficulty breathing and/or respiratory collapse resulting from paralysis of the abdominal muscleExcessive drooling
RestlessnessIncreased blood pressure and heart rate
Loss of coordination and the ability to standVomiting andĀ diarrhea

The venom is a potent neurotoxin. It triggers a release of acetylcholine and norepinephrine which causes muscle spasms and paralysis.

Most cats die of a black widow spider bite. However, there is an antivenin which can be used provided your veterinarian has it in stock or can obtain it in time.

As for the brown recluse spider, there are two syndromes apparently. The first is a “cutaneous form“. A local blister develops with pain. This is followed by a bull’s-eye lesion. Over the following week or two weeks the skin in the area of the bite will die and ulcerate. This leaves a wound which may take months to heal.

The second syndrome is a “visceral form“. A fever accompanies it together with possible seizures, vomiting and painful joints. The cat may suffer from kidney failure and blood disorders. This second form is rarer and often fatal.

What to do? As I see it, the most important thing to do is take your cat to your nearest veterinarian as a matter of urgency. My book on home veterinary care indicates that with respect to treating snake and lizard bites you should proceed to get help at a veterinary clinic within 30 minutes. Common sense tells me that the same timeframe applies to black widow spider bites.


Note: sources for news articles are carefully selected but the news is often not independently verified.

Michael Broad

Hi, I'm a 74-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I love nature, cats and all animals. I am concerned about their welfare. If you want to read more click here.

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