Black Widow Spider Bites in Cats

The fully grown female black widow spider of the familiar North American species is about 1/2 to 1 inch (1.2 to 2.54 cm) long and is typically shiny black with an hourglass-shaped red mark on the underside of the abdomen. Their preference is to live in warm, dry areas with mild winters. For this reason, they primarily live in the eastern and southwestern parts of the United States. They spin irregular webs in crevices and other dark, protected spots.

Pets most commonly are bitten by black widow spiders when they are curious and invade a nest. Both the male and female spiders are poisonous but only the female is large enough and has enough venom to affect a pet.

Black widow spider venom is categorized as a nerve toxin. One bite can be sufficient to affect severely or even kill a small pet. The venom, a neurotoxin, generally affects children more severely than adults. The spider, however, is not aggressive and bites humans only defensively. Signs of a black widow spider bite occur immediately after the bite.

What to Watch For

Death is usually due to paralysis of the muscles and nerves associated with breathing.


There is no blood test currently available to detect black widow spider venom. Diagnosis is based on the potential access to black widow spiders and physical exam findings of muscle rigidity, spasms and possible breathing difficulty.


There is an antivenin available that has been helpful in people but may be cost prohibitive in the veterinary setting. Black widow spider antivenin is usually available through human hospitals. Other treatment options may include:

Home Care and Prevention

There is no home care for a Black Widow spider bite. Do not place a tourniquet above the bite. This does not stop the venom from spreading and may severely compromise the circulation to that area of the body.Keep your cat quiet and calm and take him/her to your veterinarian as soon as possible.

The primary prevention is to limit your cat's access to areas that possibly house Black Widow spiders. Thoroughly investigate your lawn and garden for Black Widow spiders and, if seen, contact an exterminator to remove them from your home area. Be very careful with Black Widow spiders since they can also injure people