A Spider Bit Your Dog: Identifying the Bite & What You Should Do

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With over 3,000 types of spiders in the U.S. and more than 45,000 around the world, including the brown recluse, you may be concerned about one of those spiders potentially biting your favorite furry friend. Most spider bites on dogs only cause localized redness and swelling and do not require veterinary care. However, there are a few species of spiders whose bites can be life-threatening in dogs. Learn more about which spiders pose a greater threat, how to identify a spider bite on a dog and what to expect during a visit to your veterinarian.

Which Spiders Are Dangerous?

There are 11 species of spiders indigenous to the United States, and out of these, two main species of venomous spiders to be aware of are:

Close-up of a brown recluse spider

  • Brown Recluse: The most common venomous spider that bites dogs is Loxosceles reclusa, the brown recluse. They have a violin-shaped pattern on their body, and they're mostly active at night. Dogs are usually bitten by recluse spiders that are hiding in bedding, but these spiders also hide in closets, attics and dry basements. These spiders live mostly in the Midwest; however, some may be found in Southern California, southern New Mexico and western Arizona.
  • Black Widow: Black widow spiders can be identified by their shiny black bodies and a red or orange hourglass mark on their underside. Young spiders are brown, and have red or orange stripes that gradually morph into the hourglass mark as they grow older. Black widows are found in every state in the U.S. except Alaska. They like to make their homes around buildings. Only the female spiders are toxic.

Identifying a Spider Bite on a Dog

Spider bites may vary depending on the type of spider. For example, brown recluse spiders contain a venom that causes a local skin reaction in humans. There is no consensus on what these bites look like for dogs, but known clinical signs in humans include:

  • Initial pain around the bite, followed by itchiness and soreness
  • Development of a classic target lesion, which is an area of skin that loses its blood supply and turns dark, and is surrounded by redness
  • Fever, chills, rash, nausea or joint pain
  • A week to five weeks from the first bite, the dark area usually blisters and fall off, leaving a deep ulcer that doesn't heal. The extent of damage is dependent on how much venom was injected in the bite.
  • On occasion, brown recluse bites can cause anemia and kidney problems

On the other hand, black widow spiders have a venom that contains a compound called alpha-latrotoxin which is a strong neurotoxin. But according to the sixth edition of The 5-Minute Veterinary Consult, 15% of black widow bites do not contain venom and don't cause any signs other than some redness around the bite. If there is only mild envenomation, signs may not show up for weeks. If a dog is heavily envenomated by a black widow, clinical signs may include:

Black lab with tongue out sitting on a deck overlooking a bluff.

  • Tremors and cramping
  • Pain
  • Hard belly
  • Restlessness
  • Fast heart rate
  • Excessively salivating
  • Facial swelling if bitten on the face

What Should I Do If There's a Spider Bite on a Dog?

If you suspect that there's a spider bite on a dog, call your vet immediately. If your dog is already showing clinical signs, call your vet and let them know that you're coming; you may get redirected to a local emergency hospital if your vet can't see you. If you can, carefully bring the spider in a jar with you.

If you notice a bite wound, lightly apply an ice pack. Remember, when dogs are fearful or experiencing pain, they can bite. Use these tips from Fear Free Happy Homes to learn how to handle a dog that is afraid or in pain, and above all, stay calm and breathe.

If your vet recommends it, you can give your dog an antihistamine orally, like Benadryl, before you leave the house. Ask your vet for the correct dosage.

What Will Happen at the Vet?

Your vet will take your dog's vitals and conduct a full physical examination. Try to give them as much information as you can, as well as the spider if you have it. Depending on the type of spider suspected, laboratory testing and hospitalization may be recommended.

If your vet suspects that your dog has been bitten by a brown recluse, there is not much to be done initially. Bites by these types of spiders typically take a long time to heal — as long as six to eight months. Most of the care will be done at home; therefore, it's important to keep the wound clean and maintain regular contact with your vet, even if it is just weekly phone call updates. If a deep ulcer forms, then your vet will likely prescribe antibiotics to prevent a secondary bacterial infection. If your dog is in pain, pain medication will be prescribed.

If the wound becomes large with a dead area in the middle, your vet will likely recommend surgical removal of the dead tissue, and a skin graft may be required to help your dog's skin heal. If your dog is very sick, your vet may recommend hospitalization with IV fluid therapy. In rare cases, blood transfusions are required. After a brown recluse bite heals, a scar is usually left behind.

If a black widow bite is known or suspected, an antivenom is available and recommended. Your vet may hospitalize your dog, administer antivenom and fluids through an intravenous catheter, monitor for any allergic reactions to the medicine and treat any muscle spasms.

Spider and other common bug bites can be prevented by maintaining regular pest control around your property and in your home. If you live in an area where these spiders are known to reside, be sure to keep your dog out of woodpiles.

Contributor Bio

Dr. Sarah Wooten

Dr. Sarah Wooten

A 2002 graduate of UC Davis School of Veterinary Medicine, Dr. Sarah Wooten is a well-known international speaker in the veterinary and animal health care spaces. She has 10 years experience in public speaking and media work, and writes for a large number of online and print animal health publications.. Dr. Wooten has spoken in the veterinary education space for 5 years, and speaks on leadership, client communication, and personal development. Dr. Wooten is also a certified veterinary journalist, a member of the AVMA, and has 16 years experience in small animal veterinary practice. In addition to being a speaker, author, veterinarian, and co-creator of the wildly popular card game 'Vets Against Insanity', she co-owns Elevated Eateries Restaurant group in Greeley with her husband of 21 years, and together they are raising 3 slightly feral mini-humans. When it is time to play, she can be found skiing in Colorado, diving with sharks in the Caribbean, or training kenpo karate in her local dojo. Go big...or go home. To learn more, visit drsarahwooten.com.

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