Brown Recluse Spider Bites in Cats

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Last updated on
6 min read

Key takeaways

Recluse spider bite in cats occurs when an animal is bitten by a spider belonging to the recluse spider family which are found worldwide but primarily in the southwestern and southern central US.

  • The main symptoms are pain, a blister, and gradual formation of large open wounds from tissue necrosis
  • Systemic symptoms are rare and include fever, weakness, and vomiting
  • Initial diagnosis is primarily based on clinical presentation as most bites are not witnessed, and symptoms arise days after the envenomation
  • Further testing including blood tests, urinalysis, and skin biopsy confirm the diagnosis and monitor progress
  • No antivenom is currently available
  • Treatments include pain medication, wound care, IV fluids, antibiotics, and cool compresses
  • In the case of severe envenomation, especially multiple bites, affected pets may require skin grafting and aggressive supportive care
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A closer look: Brown Recluse Spider Bites in Cats

Brown recluse spider bite poisoning is generally not an emergency; nonetheless, medical attention is advised as the animal’s symptoms may progress and cause severe skin necrosis.

Brown recluse and similar, closely related spiders can be found worldwide wherever spiders live, but are commonly found in the southwestern and south central regions of the US. Brown recluse spiders rarely bite and are not considered to be aggressive; female spiders can inject twice the amount of venom compared to male spiders.

Risk factors

Recluse spider bite symptoms can be divided in accordance with the timing of onset.

I - Less than two hours from envenomation

Most animals are asymptomatic immediately following the bite and may experience only mild stinging of the bite wound.

II - Two to eight hours from envenomation

After several hours from envenomation, patients start to develop local symptoms:

  • Blister
  • Itching
  • Red skin

III - Two days after from envenomation

In the later stage of the condition, the bite wound and surrounding area start to necrotize, causing:

  • "Bull's-eye" appearance of the bite wound as the center of the blister becomes pale
  • Death of the skin tissue at the center of the blister
  • Formation of ulcerated sore

The area of affected skin varies in size depending on the amount of venom injected and may be quite large.

Rarely cats may develop complications such as:

  • Hemolytic anemia
  • Kidney damage
  • Clotting abnormalities

Possible causes

Brown recluse spider bite poisoning is caused by the bite of a brown recluse spider.

Brown recluse spiders produce venom that contains a number of necrotizing enzymes that cause tissue death (necrosis) and excessive blood coagulation.

Brown recluse spiders include:

  • Loxosceles reclusa (brown recluse spider) found in southern and central United States
  • Loxosceles rufescens (Mediterranean recluse spider)
  • Loxosceles deserta (desert recluse)
  • Loxosceles arizonica (Arizona brown spider, Arizona recluse)

Main symptoms

Recluse spider venom primarily causes localized tissue damage, not systemic toxicity.

Systemic symptoms are uncommon with recluse spider bites.

Testing and diagnosis

Spider bites are rarely witnessed, and diagnosis is based on clinical signs. There is no specific diagnostic test available, and animals presenting symptoms of brown recluse spider bite poisoning or those suspected to have been bitten generally undergo the following diagnostics:

  • Physical examination
  • Complete blood count
  • Coagulation profile
  • Serum analysis
  • Urinalysis

Steps to Recovery

Once diagnosed, treatment for envenomation is supportive and symptomatic as there is no antivenom available. Treatment primarily focuses on caring for any large open wounds that form as skin and surrounding tissues die.

Treatment options include:

  • Wound care, including surgery
  • IV fluid therapy
  • Antibiotics: antibiotics are administered to prevent secondary bacterial infections
  • Dapsone for necrotizing wounds
  • Pain medication (NSAIDs or opioids)
  • Cool compresses: if the envenomation is mild, cool local compresses on the bite site may be sufficient
  • Skin grafts

Monitoring is necessary over several weeks while waiting for the wound to heal. Complete healing may take from weeks to months. It may take several days for the extent of tissue necrosis to become apparent.

Prognosis varies widely depending on the severity of the envenomation. It is good in most cases as animals tend not to develop severe systemic symptoms, although the resulting skin damage can be quite severe. For the bite wound to completely heal, months may be necessary.


Spider bite poisoning is not contagious, but humans are as likely to be bitten as animals; prevention strategies apply to both pets and humans. Prevention strategies include:

  • Shaking bedding, clothes, towels, and other materials before use
  • Not letting pets or children wander in potentially spider-infested spaces (e.g., sheds)
  • Trimming high grass
  • Keeping pets and children away from dark areas
  • Eliminating clutter in storage areas
  • Frequent cleaning and vacuuming of warm dark areas in the house where pets lie

Is Brown Recluse Spider Bites in Cats common?

Recluse spider bite poisoning is a rare condition in cats. Brown recluse spiders are not aggressive and tend not to bite; envenomation mostly occurs if a spider is trapped in the animal's bedding.

Typical Treatment

  • Wound care
  • IV fluid therapy
  • Blood transfusions:
  • Antibiotics
  • Dapsone
  • Pain medication
  • Cool compresses
  • Skin grafts


Dominic Tauer , DVM DABT DABVT - Writing for MSD Veterinary Manual
Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM - Writing for VCA Animal Hospitals
Rosalind Dalefield BVSc PhD DipABVT DipABT, Dawn Ruben DVM - Writing for Vetlexicon
Dr. Ken Cramer and Rick Vetter - Writing for Brown Recluse Spider Project

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