Black widow spider bites in Pets

Black widow venom causes severe muscle pain and cramps, and cats are especially at risk. Learn how to recognise the spider and the signs, and why to go to a vet straight away.

What It Is

Widow spiders (Latrodectus) are glossy black spiders, the females with a red hourglass under the abdomen. Their venom contains alpha-latrotoxin, which forces nerve endings to release their chemical messengers all at once, causing severe muscle pain, cramps and rigidity. Only the larger females bite with enough venom to harm pets.

Where Pets Come Across It

Dark, undisturbed places: woodpiles, sheds, garages, outdoor furniture, shoes left outside and garden rubble. Widow spiders are found across the Americas, southern Europe, Africa and Australia (where the redback is a close relative).

Which Animals Are Affected

Cats are particularly sensitive, and Pet Poison Helpline lists severe signs and possible death in both cats and dogs. Horses can also be affected.

Published Toxic Dose

No owner-usable dose exists; venom delivered per bite varies and is unknown. The calculator shows a 'call your vet' result instead of a risk tier.

Signs and How Soon They Appear

Pain at the bite, then within hours severe muscle pain and cramping, a rigid painful belly, restlessness, wobbliness, tremors, drooling, vomiting and changes in blood pressure. Cats may cry out and become paralysed. Bites themselves are often hard to find.

What to Do Right Now

If you saw a widow spider bite your pet, or your pet suddenly shows severe muscle pain and cramping, go to a vet at once. Keep your pet calm and warm. If it is safe, trap or photograph the spider for identification. Do not cut or squeeze the bite.

Reducing spider encounters around the home

Widow spiders build untidy, strong webs in sheltered, undisturbed spots near the ground: under decking, inside garden furniture, in meter boxes, sheds and stacks of firewood or plant pots. Clearing clutter, storing firewood away from the house, and checking outdoor furniture and shoes before use all reduce encounters. Cats that hunt in sheds and garages are most exposed. Wear gloves when moving stored items. Insecticides used around the home can themselves be hazardous to pets, especially cats, so choose physical measures first and keep pets away from treated areas until products have dried. Most spiders in homes are harmless; correct identification avoids unnecessary worry and unnecessary pesticide use.

Frequently Asked Questions

Sources and References

• Merck Veterinary Manual: Spider and Scorpion Bites and Stings
• Pet Poison Helpline: Black Widow Spider

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