Spider Envenomation

Though most pet owners prefer four legged creatures, it’s important to know about the eight-legged creatures that can pose a threat to our pets. Sorry to all arachnophobes, but spider bites in our pets are a real danger! While there are many species of venomous spiders, the most common species of concern are the Black Widow and Brown Recluse spiders.  Listed below are  5 fast facts about each type of spider:

Black Widow (Latrodectus sp)

  1. These spiders have the tell-tale red orange hourglass or ink blob pattern on the underside of their abdomen. Adult spiders are shiny, black, and approximately the size of a penny in diameter. Juvenile spider can be more brown or beige in color, and still pose a threat.
  2. Black Widows are found in all 48 continental states, Hawaii, and southern Canadian provinces. There is also a Brown Widow spider recently found in the southern and western USA.
  3. ALL species of animals (including humans!) are susceptible to Black Widow venom. Cats are particularly sensitive to the venom, and bites are often lethal in our feline companions. Horses and camels are also highly sensitive to Black Widow venom.
  4. Signs of a Black widow envenomation include sudden and severe pain at the bite site, weakness, lethargy, muscle pain, seizures, collapse, and even death.
  5. The venom from a Black Widow bite acts within minutes, so immediate veterinary care is always needed. While there is an antidote available, most veterinary clinics don’t have it on hand, and they may need to contact a local human hospital or pharmacy.


Brown Recluse (Loxosceles reclusa and others)

  1. Otherwise known as the violin spider, Brown Recluse spiders are shades of brown with dark violin-shaped marking on their thorax and are roughly the size of a quarter. These spiders have six eyes in contrast to most spider species having eight eyes.
  2. Brown Recluses are found in the southern and midwestern portions of the United States.
  3. ALL species of animals (including humans!) are susceptible to Brown Recluse venom. Dogs are especially sensitive.
  4. Although most bites result in mild skin irritation, the development of ANY other symptoms are signs of a significant envenomation! It can take 2-7 days to see signs of a Brown Recluse bite. If you notice any skin lesions (like pain, itching, bulls-eye lesion, or other rashes) or notice lethargy, weakness, or seizures, seek veterinary care as soon as possible.
  5. While there is no antidote, most animals make a full recovery with veterinary supportive care.


If you suspect you pet was bitten by or exposed to a Black Widow or Brown Recluse, it is important to act quickly. Immediately contact your veterinarian or Pet Poison Helpline for further instructions and recommendations.


Written by:

Abigail Gilman, DVM student extern, Iowa State University Class of 2023

Lizzy Olmsted, CVT, Veterinary Information Specialist Pet Poison Helpline