Why it's dangerous
Spiders inject venom through bites which can cause localized tissue damage, inflammation, and in severe cases, systemic organ failure or clotting abnormalities.
How vets treat it
No lab test confirms a spider bite, so vets go by the signs, where you live and what you saw. Pet Poison Helpline names cats as the kind of severe black widow case that calls for antivenom. Given into a vein, it can relieve signs quickly. Vets watch for allergic reactions and often give an antihistamine first. Cats also get hospital care: pain relief, medicines for cramps and seizures, IV fluids, anti-nausea medicine and blood pressure checks. There is no brown recluse antivenom in the US. For pets in general, vets clean and bandage the wound, use cool compresses and rest, give antibiotics if it gets infected and treat pain. If the whole body is affected, the pet stays in hospital for IV fluids to protect the kidneys and care for anemia and clotting problems.
Outlook
Bites from most spiders cause only mild irritation, though any bite can become infected. A black widow bite is serious: cats are highly vulnerable to the venom, and the Merck Veterinary Manual and Pet Poison Helpline say deaths are common. Recovery can take several weeks, especially without antivenom. Sources give no cat-specific outcome data for brown recluse bites. For pets in general, most recover with supportive care, illness through the whole body and death are rare, and most wounds heal in 1 to 8 weeks.
Where pets are exposed
- Nearly all spiders have venom, but most can't bite through a pet's skin or inject enough to cause illness. In North America, two groups cause real harm: widow spiders, such as the black widow, and recluse spiders, such as the brown recluse.
- Black widows live across the lower 48 US states, Hawaii and southern Canada. The brown recluse lives mainly in the central and southern US.
- Dark, quiet places where curious pets sniff or paw at spiders: garages, sheds, basements, behind or under furniture, woodpiles and debris piles, holes, around foundations and under windowsills.
- Widow spiders are timid and usually bite only when touched by accident or when their web or egg sacs are disturbed. Brown recluses are shy too: pets usually get bitten when they lie or roll on one, for example in bedding.
- A cat or dog catching or playing with a spider. Encounters rise in late summer and early fall, when spiders are most active, and recluse spiders are more active in warmer months.
Prevention
- Clear webs and clutter from garages, basements, sheds, dark corners, behind furniture and under cabinets.
- Keep the yard free of debris, and sweep webs off foundations, porches, play sets, picnic tables and windowsills.
- Supervise pets in garages, sheds and other little-used areas. On walks, keep dogs on a leash and away from holes, woodpiles, debris piles, logs and foundations.
- If you find a widow spider nest or have many spiders, have a pest professional remove or relocate them rather than handling them yourself.
- If you see your pet playing with a spider, move your pet away first, then relocate the spider.
- If you keep a pet tarantula, keep dogs and cats away from it. Its flicked hairs can irritate their skin and injure their eyes.
Good to know
The black widow and brown recluse are the most dangerous; females are generally larger and more venomous than males.
Common questions
Are spider bites dangerous to dogs and cats?
Usually not. Nearly all spiders have venom, but most can't bite through a pet's skin or inject enough to matter, so a bite usually causes at most a small, itchy red bump. In North America the real dangers are widow spiders, such as the black widow, and recluse spiders, such as the brown recluse.
Is a black widow bite more dangerous for cats than dogs?
Yes. Cats are highly sensitive to black widow venom, and both Merck and Pet Poison Helpline say bites are often fatal for them, so treat any suspected bite in a cat as an emergency. Dogs are more resistant and have a better outlook (Merck calls it good, Pet Poison Helpline fair), but they can still get very sick.
How do I know if my pet was bitten by a spider?
Often you can't. A brown recluse bite is usually painless and goes unnoticed, a black widow bite mark is often impossible to find, and the spider is usually gone by the time signs appear. Spider bites can also look like insect stings, allergic reactions or skin infections. The only sure confirmation is identifying the spider.
What should I do if I think a spider bit my pet?
Move your pet away from the spider without getting bitten yourself. If you suspect a black widow or brown recluse, or your pet has any sign beyond a mild red bump, call your vet, an emergency clinic or a pet poison line right away. If it's a cat and a black widow may be involved, go straight to the vet. Don't give medicines or home remedies unless a vet tells you to.
How long after a spider bite do symptoms show in pets?
It depends on the spider. Black widow signs can begin within minutes and usually appear within 8 hours. A brown recluse bite can blister within 2 to 8 hours, and rarer whole-body signs can take several days. For a mild red bump, see a vet if it isn't better, or is getting worse, within 24 hours.
Is there antivenom for spider bites in pets?
There is an antivenom for black widow bites. It can relieve signs quickly, but most vet clinics don't stock it and may need to get it from a human hospital, and vets decide case by case because it can cause allergic reactions. There is no brown recluse antivenom in the US, so those bites are treated with wound care and supportive care.
Sources
- Merck Veterinary Manual — Spider and Scorpion Bites and Stings to Animals
- ASPCA Animal Poison Control Center — ASPCA Poison Control
- ASPCA Animal Poison Control Center — What to Do if Your Pet Is Poisoned
- Pet Poison Helpline — Spiders
- Pet Poison Helpline — Spider Envenomation
- Pet Poison Helpline — Widow Spider Envenomation: A Concern for the Curious Pet
- Texas A&M College of Veterinary Medicine & Biomedical Sciences — Untangling the Web: How to Handle Spider Bites in Pets
- VCA Animal Hospitals — Spider Bites
- Pet Poison Helpline
This page is informational and is not veterinary advice. If your pet has been exposed to something risky, contact your vet or an animal poison control line right away.
