Brown Recluse Spider Bites on Cats

Brown Recluse Spider Bites on Cats


When a brown recluse spider bites a cat, venom is injected into the site. This venom has a component that destroys red blood cells and kills the surrounding tissue in cats. These bites are rarely fatal for cats, but in systemic cases where the cat has a poor immune response, they can cause kidney failure.

Brown recluse spiders occur throughout the United States, but are found most commonly in the Midwest and Southeast. These spiders will usually not bite unless disturbed, so curious cats are the most likely to be bitten. Because the bite is often painless, your cat may not even know it was bitten until 2 to 3 hours later. By this time, the spider will likely have left the area. Because of this and because many things can cause deep lesions, there is often misidentification of the spider and brown recluse spider bites are often misdiagnosed.

Signs & Symptoms of Brown Recluse Spider Bites on Cats

 Symptoms are dependent on how much venom is injected into the bite site and how your cat’s body reacts to it. In a small percentage of cases, a systemic reaction may occur, usually 24 to 48 hours after the bite. Symptoms include fever, joint pain, weakness, vomiting, seizures, blood disorders, and kidney failure.


10 minutes after bite:

  • Constriction of capillaries around bite site

2 to 6 hours after bite:

  • Red, swollen area surrounding the bite site
  • Localized pain surrounding the bite site
  • Fever
  • Nausea

12 hours after bite:

  • Blister forms at bite site

7 to 10 days after bite:

  • Rapid cell damage surrounding the bite site
  • Bite site with a black center


Causes of Brown Recluse Spider Bites on Cats


There are about fourteen Loxosceles species of brown spiders found in the United States, but the most common of these that bites domesticated cats is the brown recluse spider, Loxosceles reclusa. The brown recluse spider typically hides indoors in dry, undisturbed areas such as closets, basements, and attics. The bite of a brown recluse spider causes the blood vessels in your cat to narrow, increasing their blood pressure. The area around the bite becomes red and swollen and may form a blister. The venom will kill any cell it contacts and may form a painful crater of dead tissue within 3 to 4 days. The extent of the tissue damage is dependent on how much venom is injected into your cat at the time of the bite.


Treatment for Brown Recluse Spider Bites on Cats


If you suspect your cat has been bitten by a brown recluse spider, these actions should be taken: 

  • Apply an ice pack to the bite site to reduce pain and swelling.
  • If you see the spider, CAREFULLY try to catch it in a jar for later identification.
  • Contact your veterinarian immediately.


Brown recluse spider bites usually take a long time to heal, and it may take 6 to 8 months to heal completely. If black necrotic tissue has formed, it may fall away and expose the muscles underneath. It is very important to keep these wounds clean to avoid infection. A sunken scar will usually develop.


Prevention of Brown Recluse Spider Bites on Cats


Though the chance of seeing the spider is slim, being able to identify the spider that bit your cat may help get your cat the proper care faster.


The best way to prevent a brown recluse spider bite is to limit your cat’s exposure to the spider. Check old storage boxes and rarely used areas of your house for spiders, and if a brown recluse is seen, call an exterminator as soon as possible. An infestation could take as long as six months to resolve. However, there are certain measures you can take on your own, such as exclusion, sanitation, or control.



  • Seal off all windows and doors to ensure that no pests can enter
  • Seal cracks in your home to keep pests out
  • Reduce the number of other insects around your home
  • Make sure everything you store away is sealed tight


  • Remove unwanted items and boxes that may provide hiding spots for the pest
  • Remove dead insects that the spider may feed on
  • Do not keep wood stacked near your home
  • Keep your home clean and uncluttered


  • Capture individual spiders
  • Use sticky tape or glue traps to capture spiders