Brown Recluse Spider Bite Poisoning in Dogs

The brown recluse spider (loxosceles reclusa) is not aggressive and will not bite unless stepped on or crushed. Small bites can be non-symptomatic, but the spider’s hemotoxic venom does have the potential to be fatal, especially in small dogs. The brown recluse spider is most recognizable by the violin shaped mark on its back. It builds irregular shaped webs under logs or rocks, or inside the house in a closet or a cardboard box. Most bites are caused by the dog lying or walking on the spider. 

The immediate bite doesn’t usually cause pain, but signs may appear in 4-8 hours. A red, itchy skin lesion develops around the site. The bite may sometimes have a bullseye look with a white center or a ring around the outside. There may be a blistered area as well as considerable redness and swelling. Brown recluse spider venom causes necrosis in the skin (cell death). As signs progress, the dead cells will turn black and fall off leaving a gaping wound that may be as big the width of a hand. 

The area will eventually heal, although it may take a number of months. If a lot of venom is injected, or the dog is very sensitive to the venom, a systemic infection can develop. This is less common, but it can lead to serious problems including anemia, blood clots, and kidney failure. In severe cases, the bites can be fatal. There is no antidote, but early treatment with corticosteroids can reduce the chances of a systemic infection.

The majority of spider bites are harmless to dogs. Only a few spiders have venom strong enough to cause significant signs in such a small dose. The brown recluse spider is one of these, found most commonly in the southern and midwestern parts of the United States. In dogs, bites can infect the skin and sometimes cause systemic illness.

Pain, or reluctance to put weight on one leg may be the first signs of a spider bite. Signs of a skin infection around the bite will appear within a few hours. These signs should be treated by a veterinarian to avoid further problems.

• Signs of pain
• Skin lesion that is red, itchy and painful
• Skin lesion with a bulls-eye effect
• Swelling
• Blister
• Bruised, inflamed area spreading around the lesion or blister
• Necrotic tissue (black area of dead skin cells) around the bite
• Hole or wound after the damaged tissue has fallen off
• Scab that may take months to heal

A systemic infection can take up to 4 days to appear. These are the signs to look for.

• Thirst
  
• Fever
  
• Vomiting
  
• Nausea
  
• Anemia
  
• Water retention (edema)
• Renal failure
• Shock

Types

There are quite a few spiders in the loxosceles genus, but the brown recluse is the most common. A bite by another type of loxosceles spider will cause approximately the same signs. A bite by the hobo spider, a more aggressive house spider found in the northwestern United States, can also cause similar skin necrosis.

Brown recluse spiders need pressure in order to inject venom. These are some of the reasons your dog might get bitten.

• Walking through a spider web
• Sitting or lying on a spider
• Investigating a dark secluded place such as a hollow log
• Digging through dry leaves
• Sleeping under a porch
• Spider infestation in a kennel

In most cases, the owner will not see when their dog gets bitten. Dogs don’t usually show visible pain and many bites occur when the dog is alone. The veterinarian will physically examine the area and ask for a detailed description of the symptoms, including when you first noticed the problem. He will take your dog’s temperature, vital signs, and bloodwork to check for anemia and other symptoms of systemic illness, as well as evaluate the possibility of other causes.

The appearance of the bite and the skin necrosis around it is usually a good indication of a brown recluse spider bite, depending of course on the location. If you did see the spider the veterinarian will ask for a description. Brown recluse spiders are between 6 and 20 mm across. They are typically light brown, but there can be a good deal of color variation. The black violin shaped mark on the front, head-part of the abdomen is the most distinctive mark. The spiders also have only three pairs of eyes, unlike most spiders which have four, but this is not easy to see without a magnifying glass.

An ice pack is a good first treatment for redness and swelling. Get to the veterinarian as soon as possible as early treatment can prevent more severe illness. Corticosteroids are often prescribed. In the early stages, this can stop the necrosis from spreading too much. It can also help to contain the venom in the infected cells and protect against systemic illness. The veterinarian will suggest you monitor your dog closely for further signs. 

Dogs that are very ill will be given fluids and electrolytes as needed. Severe anemia and blood clotting problems could require blood transfusion. The most common drug used to treat brown recluse spider in humans and dogs is a leprosy drug called dapsone. This may be prescribed for more severe cases.

Antibiotics are usually given to prevent infections from developing. The veterinarian will likely also give you an antiseptic solution to clean the area. This will have to be done several times a day. The wound will need to be covered with a bandage. In some cases, tetanus shots are also given.

Most dogs make a complete recovery from brown recluse spider bite poisoning. However, it can take many months for the wound at the infection site to fully heal, and sometimes scars are left behind. If this is a problem, show dogs can have plastic surgery to remove the mark.

The best way to manage the problem is to prevent it. Many bites occur because of an infestation of spiders in a house, a kennel, or some other place the dog goes regularly. Spraying for spiders and other insects frequently can help prevent this. It’s also a good idea to become familiar with all the poisonous spiders and other animals in your area, so you can recognize them immediately. Familiarize yourself with the signs of poisoning and get your dog treated right away.

Paying to treat a brown recluse spider bite out of pocket can be a major financial burden. Fortunately, most pet insurance companies reimburse claims within 3 days, putting 90% of the bill back in your pocket. In the market for pet insurance? Compare leading pet insurance companies to find the right plan for your pet.