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Black Widow Spider

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Poisonous to: Cats, Dogs

Level of toxicity: Generally moderate to severe/life-threatening

Common signs to watch for:

  • Severe muscle pain
  • Cramping
  • Walking drunk
  • Tremors
  • Paralysis
  • Blood pressure changes
  • Drooling
  • Vomiting
  • Diarrhea
  • Death

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Black widow spiders (Lactrodectus spp), which are found throughout North American (except for Alaska), are poisonous to dogs and cats. Female black widow spiders typically are 2-2.5 cm in length, are black, shiny, and have an orange or red hourglass mark on their underside. Immature females are brown in color, and the hourglass shape darkens with age. Males are brown and lack the hourglass mark, and are generally considered non-toxic due to the small size of fang/bite. These spiders carry a potent venom which is a neurotoxin (a-latrotoxin). Dogs and cats bitten by black widow spiders may show clinical signs of severe muscle pain, cramping, walking drunk, tremors, paralysis, blood pressure changes, drooling, vomiting, diarrhea, and death. Treatment includes the use of an antivenom, IV fluids, anti-seizure medications, pain medications, and symptomatic supportive care.

If you suspect your dog or cat were bitten by a black widow spider, call your veterinarian or Pet Poison Helpline immediately for life-saving care.

Poison type: Envenomations

Alternate names: Lactrodectus, spider, a-latrotoxin