ASK THE VET: Cats especially sensitive to Black Widow venom

Q: Our indoor-outdoor cats are fascinated by the spiders and spider webs around our house. I am concerned that some of the black, shiny spiders could be black widows. Are black widow spiders dangerous to cats?

A: Cats are especially sensitive to the toxin of the black widow spider, the most venomous spider in North America.

About an inch long, the black widow spider is shiny black or brown with a red or orange, hourglass-shaped mark on the underside of its abdomen. Black widows live in and around houses throughout the U.S. (except Alaska) and southern Canada, where they spin funnel-shaped webs.

The black widow was named because the female kills and devours the male after mating, leaving her a "widow."

The black widow's venom is more potent than rattlesnake venom, though only females can envenomate mammals. While these spiders have venom glands, venom is actually present throughout the spider's body and even in her eggs.

The female black widow's fangs are long enough to penetrate animal and human skin. In addition, cats often toy with and then eat these spiders. So, cats are harmed through bites and by ingesting the spiders.

Fortunately, black widows are not aggressive. They bite only when provoked or when their webs are disturbed.

When they do bite, black widows inject a potent neurotoxin that is particularly dangerous to cats. Clinical signs begin within a few hours, peak at 24 hours, and persist for days to weeks.

Clinical signs include pain at the site of the bite without much skin damage, a rigid abdomen without abdominal pain, restlessness, tremors, seizures, weakness, salivation, emesis, diarrhea, paralysis and respiratory collapse.

The most important part of treatment is antivenom, which can be given up to 24 hours after the bite and is rapidly effective. Intensive hospital care is also required.

Although they only very rarely cause human fatality, without treatment, these bites are often fatal to cats. In one study, 20 of 22 cats died, on average 4.8 days after envenomation.

Please keep your cats away from all black widows and their webs so the spiders can accomplish their mission of catching insects and your cats can remain safe.

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Q: Boomer, my Lab mix, has arthritis and skin allergies. A friend suggested giving him flaxseed or flaxseed oil because it is a good source of the omega-3 fatty acids that can help both problems. Is flaxseed safe for dogs?

A: Yes, it's safe, but it's not effective in dogs.

Flaxseed, flaxseed oil, canola oil, soybeans and walnuts contain alpha-linolenic acid, or ALA, which humans convert into two beneficial omega-3 fatty acids: eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA.

However, the metabolism of dogs — and cats, for that matter — is different. They can't convert ALA into EPA or DHA.

Therefore, Boomer needs actual EPA and DHA, which is present in fish, krill and algal oils.

EPA and DHA are effective in the management of pets' osteoarthritis, also called degenerative joint disease, as well as their allergies, kidney disease, heart disease and cancer.

I recommend you get Boomer's fish oil from his veterinarian. Or you may buy an omega-3 fatty acid supplement marketed for humans, as long as the ingredient list includes EPA and DHA.

Lee Pickett, VMD, practices companion animal medicine in North Carolina. Contact her at

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