Toxic to dogs · Bites & stings

Are Spiders toxic to dogs?

Moderate severity

Yes, Spiders are toxic to dogs. They can cause real illness, so contact your vet if your pet has been exposed.

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Are spider bites dangerous to dogs and cats?

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What to do right now

  1. Move your dog away from the spider, but don't risk a bite yourself. Most people can't safely identify or catch a spider.
  2. If you saw a bite, or think a black widow or brown recluse was involved, call your vet or an emergency clinic now. Don't wait for signs. In the US, you can also call Pet Poison Helpline (855) 764-7661 or ASPCA Animal Poison Control (888) 426-4435 (fees may apply).
  3. Call ahead so the clinic is ready. Most vet clinics don't stock black widow antivenom and may need to get it from a human hospital or pharmacy.
  4. For a known black widow bite, you can wash the bite with mild soap and water for a minute or two. This won't stop the venom, but it may help prevent infection. Don't let it delay the trip.
  5. Don't give your dog any medicine or home remedy unless a vet or poison-control expert tells you to.
  6. If your dog only sniffed or played with a spider and seems normal, or has just a small red bump, keep watching. See a vet if the bump isn't better, or is getting worse, within 24 hours. Go right away if any other sign appears.
  7. Identifying the spider is the only way to confirm a spider bite. If you can collect the spider or its remains without touching it barehanded, bring it to the vet.

Go to an emergency vet if

  • You saw a black widow bite your dog, or found one near a dog that now seems unwell.
  • Your dog has muscle cramps or pain, a hard belly, trembling, restlessness or drooling, vomits, or walks as if drunk.
  • Your dog has trouble breathing, weakness or paralysis, or a seizure, or collapses.
  • After a possible brown recluse bite, your dog seems tired or weak, has a fever, vomits, or has red or dark urine or unusual bruising or bleeding.
  • A bite wound blisters, forms a bull's-eye, turns dark or keeps spreading. See a vet as soon as possible.

Symptoms to watch for

  • Redness to the skin
  • Bite wound
  • Swelling
  • Inflammation to the skin
  • Pain to the touch
  • Warmth or hot feeling to the touch
  • Necrosis of the skin
  • Bruising
  • Vomiting
  • Scabbing of the skin
  • Local itchiness of the skin
  • Organ failure
  • Fever
  • Abnormal clotting

How much is dangerous

No source gives a toxic amount of venom. Most spiders can't inject enough venom to harm a pet. With a female black widow, though, a single bite can be enough to kill one. Dogs are more resistant to black widow venom than cats, but they can still become severely ill. The spider controls how much venom she injects, and some bites inject none. Male black widows are not a real risk, because their fangs are too small to break through skin.

When signs appear

After a black widow bite, signs can start within minutes, and severe signs usually appear within 8 hours. Muscle pain and cramps start near the bite 1 to 2 hours later, then spread to larger muscles. Signs can come and go for a couple of days. After a brown recluse bite, a blister can form at the bite within 2 to 8 hours. Illness through the whole body, if it happens, can take several days to show: Pet Poison Helpline says 2 to 7 days.

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. For a black widow bite, treatment is hospital care, often over several days, to control pain and muscle cramps: pain relief, muscle relaxants, IV fluids, anti-nausea and anti-seizure medicines, and blood pressure checks. Antivenom given into a vein can bring quick relief, but many dogs don't need it and it can cause allergic reactions, so vets decide case by case. There is no brown recluse antivenom in the US. Vets clean the wound, use cool compresses and bandages, prescribe rest, and treat pain and any infection. A dog that is ill through the whole body 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 if it isn't cared for. After a black widow bite, Merck rates the outlook for dogs as good and says many need no treatment. Pet Poison Helpline calls it fair with supportive care. Recovery can be slow: it can take several weeks, and weakness and tiredness can last for months. After a brown recluse bite, most pets recover fully with supportive care. Most wounds heal in 1 to 8 weeks, but some take months. Illness through the whole body is rare, but it can be fatal.

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

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.

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