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Many people have a fear of spiders, but it seems like few dogs share that fear. Dogs often shove their noises into dark nooks and crannies that spiders often call home, some of which are venomous. Dogs also tend to sleep in places more likely inhabited by spiders. The result? Your dog may be bitten by a spider.

The problem is that people can usually tell their doctors about a spider bite, and dogs can’t. So it’s up to the owner to recognize the signs of a spider bite and to know which bites are potentially serious or even fatal.

How to Tell if a Spider Bites Your Dog

What should you do if you think your dog was bitten by a spider? Consider taking your dog to the vet to be evaluated, just in case. While some bites go undiagnosed, other non-bites can be incorrectly attributed to spiders. Knowing what venomous spiders live in your area is also really helpful. Most often, you won’t see the spider actually bite your dog, so knowing what to look for can help you identify when you’d need to take action.

The action you should take depends on the type of spider that you think bit your dog, and symptoms vary depending on the spider. But with more than 3500 types of spiders in the U.S. alone, you’d have to be a spider expert to recognize even half of them. Fortunately, there are only a handful of spiders that cause problems with dogs. This is typically because many of these spider’s mouths are too weak and fangs are too short to pierce a dog’s skin, or because their toxin isn’t strong enough to cause an issue for your dog. But there are some spiders that can cause at least local irritation, and others whose toxins are fatal. Spiders like the black widow and brown recluse are both common, and have bites that are generally serious for dogs, but there are a few more that you should look out for.

Sick Labrador Retriever laying on an operating table.
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Common Types of Spiders that Bite

Black Widow

If your dog is bitten by a black widow spider, this is an emergency. The female black widow is the most recognizable venomous spider, identified by its round, shiny black body with a red or orange hourglass on the underside. Immature spiders have red or orange stripes, and perhaps a brownish body, but they can also produce venom.

Black widows are found in every U.S. state except Alaska, but are most common in the south and southwest U.S. and tend to live in dark, undisturbed areas. Dogs coming in contact with their webs is how they usually get bit. Their webs are usually built between debris or secluded corners near the ground, and the spider is typically close by.

The jaws of the male spiders are too small to puncture a dog’s skin, but females are bigger and can easily bite a dog. Their bites leave two tiny puncture marks and are extremely painful. The pain starts at the bite site and spreads throughout the body. Signs can occur as soon as 30 minutes following the bite, and worsen over the next 8 hours. The venom is a neurotoxin, meaning it affects the nervous system. It’s actually 15 times more deadly than rattlesnake venom, but of course, a lot less of it is injected. Signs of black widow bites in dogs can include:

  • Pain, often evidenced by whining and crying
  • Severe muscle spasms
  • Tremors
  • Difficulty breathing
  • Stumbling
  • Vomiting, drooling, or diarrhea
  • Stomach cramps
  • Increased heart rate and blood pressure
  • Seizures
  • Paralysis
  • Death
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The severity of the bite depends on many factors, including how big the spider is, how small the dog is, whether the dog is very old, very young, or otherwise sick, and the bite location. If you suspect your dog has been bitten by a black widow, consider it an emergency and contact your veterinarian immediately. No home treatment is available.

Blood tests may reveal an elevated enzyme called creatine kinase, which can be indicative of muscle damage caused by the venom. However, there is no definitive test to diagnose a black widow bite specifically.

Treatment is mostly supportive, meaning it focuses on treating the symptoms. That can include IV fluids, muscle relaxers, pain medication, medications to combat seizures, and anti-nausea medication. An antivenom is available but few veterinarians stock it, plus it can cause severe anaphylactic reactions in some dogs. For this reason, antivenom (when available) is reserved for the most serious cases. Dogs may spend two to three days hospitalized if they’re bitten by black widows, and they may take weeks to months to fully recover.

Brown Recluse

If a brown recluse spider bites your dog, this is an emergency. This spider is brown, with a darker, violin-shaped area on its back, with the “neck” of the violin facing away from the head of the spider. The shape is very light in young spiders and gets darker as the spider ages, which means it may not be noticeable in all brown recluses. The spider also has six, rather than eight, eyes. The legs are plain tan and long. The body is no greater than half an inch in size.

The brown recluse is found mostly in the Midwestern and southern United States, ranging from Louisiana along the Mississippi River into northern Illinois, and east as far as Tennessee and Georgia. It is also occasionally found in southern California, southern New Mexico, and western Arizona. They prefer dry, sheltered areas, such as beneath rock piles or when inside, in closets or shoes. Dog bedding can also be inviting.

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The brown recluse can only bite if it has counter-pressure, meaning it must have something to push against in order to pierce the skin. With dogs, this can happen if they lie on top of a brown recluse. Brown recluse bites on dogs most often occur on the legs. The brown recluse’s venom contains enzymes that kill surrounding tissues. A bite may not be painful at first, and may be a bit red or itchy.

Within 2 to 8 hours, the toxins will have begun to kill enough tissue to be evident. The bite turns white or purple and is surrounded by reddened skin. This bull’s-eye pattern is very common with a brown recluse bite. The bite area continues to expand in area and depth, with dead tissue turning black. Toxins from the dead tissue can make the dog sick, and if the venom enters the bloodstream, organs can begin to fail.

Other signs that can develop in the next day to several days include:

  • Anemia
  • Red or brown urine from the presence of blood cells
  • Fever
  • Vomiting
  • Lethargy and weakness
  • Slowed clotting, with increased bruising
  • Kidney and liver damage
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If your dog shows any of these signs (especially if you live in an area where you’ve seen brown recluse spiders), contact your veterinarian immediately. There is no home treatment for a brown recluse bite. Blood tests can diagnose problems typically associated with a brown recluse bite, such as anemia, clotting abnormalities, or organ failure, and urine tests can detect blood in the urine.

If diagnosed early enough, a drug called Dapsone can reduce tissue death. Otherwise, antibiotics, pain medication, and wound treatment are the main treatments. In severe cases, blood transfusions and even surgery may be recommended. Complete healing may take one to eight weeks.

Chilean Recluse

If a Chilean recluse spider bites your dog, this is an emergency. This relative of the brown recluse is more dangerous but less common. It has a brown body with a black line that like the brown recluse, resembles a violin. Not all have the brown recluse’s black marking, however. Like the brown recluse, it has only six eyes instead of eight.

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Although mainly inhabiting South America, the Chilean recluse is also established in the Los Angeles area. Infestations have been found in Florida, Massachusetts, and Kansas. Habitat, biting circumstances, bite appearance, signs, and treatment are similar to the brown recluse. Its venom is actually more toxic, however, and has been responsible for a number of human deaths in South America.

Red Widow

If a red widow spider bites your dog, this is probably an emergency. A relative of the black widow, the red widow has the same body shape but different coloration. The upper body is orange-red, and the lower abdomen is black with bright red markings that can be hourglass, triangular, or other shapes.


It is found only in the palmetto scrubland and sand dune habitats of central and south Florida. Its bite injects less toxins compared to the black widow, but enough that it could still be dangerous to a dog, especially a small dog. Symptoms and treatment are similar to those for the black widow’s bite.

Brown Widow

If a brown widow spider bites your dog, this could be an emergency. The brown widow has a brown body, long legs, and orange or red markings on its abdomen. It’s smaller than the black widow.

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The brown widow is found in Hawaii, Southern California, and in the Gulf states, and has been recently found in Georgia and South Carolina. Compared to black widows, brown widows choose habitats that are more exposed, such as recessed garbage can hand grips, beneath railings, in mailboxes, and similar areas.

Its venom can be as toxic or even more toxic than the black widow’s, but it injects far less. Most symptoms are confined to the bite area. However, especially in smaller dogs, brown widow venom could cause pain, vomiting, and muscle rigidity.

Preventing Spider Bites in Dogs

If you’re concerned about spider bites, your first step is to remove as many spider-friendly habitats from inside of and around your house. That generally means cleaning out dark corners, sealing cracks and crevices, getting rid of wood piles and stone mounds, and sweeping away leaves and debris. Insect glue traps can capture many spiders but should not be placed where other animals can come into contact with them.

Some insecticides can rid nooks and crannies of spiders, but you may have to call a pest control service. If you use either of these options, make sure they’re non-toxic for dogs. Discourage your dog from nosing around in dark corners, under piles of rocks and wood, or beneath leaves.

Clean your dog’s bedding and make sure it’s not next to doors, windows, dark corners, cracks, or crevices. Consider using raised beds when possible. And clean, clean, clean!

This article is intended solely as general guidance, and does not constitute health or other professional advice. Individual situations and applicable laws vary by jurisdiction, and you are encouraged to obtain appropriate advice from qualified professionals in the applicable jurisdictions. We make no representations or warranties concerning any course of action taken by any person following or otherwise using the information offered or provided in this article, including any such information associated with and provided in connection with third-party products, and we will not be liable for any direct, indirect, consequential, special, exemplary or other damages that may result, including but not limited to economic loss, injury, illness or death.
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