Widow Spider Envenomation: A Concern for the Curious Pet

Renee DiPietro, LVT
Associate Veterinary Information Specialist
Pet Poison Helpline®

Widow spiders have long struck fear into hearts and minds. Tales are told of the dangers of this venomous arachnid and how she kills her partner after mating. While it is important to take heed of this spider and avoid disturbing her or her nest, her notoriety may be somewhat exaggerated.

Scientifically this spider is known as Latrodectus. There are 5 species in the United States. The Northern Black Widow Spider (Latrodectus variolus), the Southern Black Widow Spider (Latrodectus mactans), the Western Black Widow Spider (Latrodectus hesperus), The Red Widow Spider (Latrodectus bishopi), and the Brown Widow Spider, (Lactrodectus geometricus).

Together their ranges combine to cover most of the United States (found in every state except Alaska), Southern Canada, and Mexico.

The further south you go, the more common this spider is. I have lived in Vermont, Connecticut, and Quebec for most of my life and never saw a Black Widow or even knew I shared a geographic range with them.  Since moving to Virginia 10 years ago I have en countered several female Black Widow Spiders. I have met them in my kayak with a collection of egg sacs, scurrying through my hay bales, catching termites in my spring house, and walking across my desk (this lady was less shy than most).

The mature female Black Widow is a very recognizable spider.  She is a glossy black with a very round abdomen. If a view of the ventral (bottom) aspect of her abdomen can be obtained, a red hourglass shape is a definitive identifier. The shape of the symbol can vary in individual spiders and is sometimes only seen as red spots.

She is very beautiful spider that always gives me pause both for her distinctive appearance and my desire to stay out of her way.  It is a myth that she always kills her mate though this can at times occur.

Less common are the Red and Brown widow spiders.

Red Widows have red legs and a black abdomen spotted with white ringed red spots. The hourglass may be less visible on the ventral abdomen.

Brown Widows are brown in color with a white and brown spotted abdomen (may be less bulbous then the Black and Red Widows) and have the classic red hourglass on the ventral aspect of the abdomen.

The male and immature spiders are not as distinctive looking as the mature female. The male is significantly smaller, striped orange and brown, and lacking the distinctive red hourglass. Immature females can be greyish brown with stripes. Some semblance of the hourglass shape in lighter colors than the vibrant red on the mature female, may be seen on the male and immature females.

The female Widow spider is truly venomous, and it is estimated that her venom, a powerful neurotoxin (a-latrotoxin), is 10-15 times as powerful of that of Rattle Snake venom. That being said, a female spider can only deliver a small (compared to a snake bite) amount of venom at one time. Immature females have potent venom but in smaller quantities. Male spiders have small fangs that cannot penetrate human or animal skin and are of little threat. The female widow spider can live up to 3 years while the male’s life span is often only 2-3 weeks.

Widow spiders are timid and build their webs close to the ground and in dark secluded places.  They generally only bite when their web or egg sacks (stored in or near web) are threatened. They will often try to escape or will even at times play dead if encountered away from their webs. Pets can encounter widow spiders if sniffing in holes, in debris piles, around foundations, in basements, under windowsills etc.

The bite of a female widow spider can cause significant clinical signs for a pet or person. The musculoskeletal, nervous, cardiovascular, gastrointestinal, and respiratory symptoms can all be affected. Clinical signs can develop almost immediately and up to 2-3 hours or more after the bite occurs.

Common clinical signs include:

  • Localized tissue inflammation
  • Wide-spread muscle spasms, pain, and cramping
  • Weakness and lethargy-can last months
  • Ataxia (walking like drunk)
  • Tremors
  • Paralysis
  • Blood Pressure effects
  • Hypersalivation (drooling)
  • Vomiting
  • Diarrhea
  • Death

Cats are very sensitive to Black Widow venom and envenomation is often fatal. Horses are also highly affected by envenomation.

Dogs can have a fair prognosis with supportive treatment.

Widow Spider bites are rarely fatal to humans.

If you know or suspect your pet has been bitten by a widow spider, we recommend seeking immediate veterinary attention.

If the bite was sustained by a dog, you can take a minute or two to clean the area with mild soap and water. This will not reduce the effect of the venom but may help to prevent secondary infections.

If the affected animal is a cat, this can be a life- threatening emergency and no time should be lost in seeking veterinary evaluation and care. If a horse is bitten, call your large animal veterinarian as soon as you are aware that this exposure has occurred.

Once you have your pet admitted to your veterinary clinic or you have called your large animal veterinarian, starting a case with Pet Poison Helpline® can provide expert and valuable aid to your veterinarian.

Treatment administered by your veterinarian is generally symptomatic and supportive and may include:

  • Baseline and subsequent bloodwork
  • IV Fluid Therapy
  • Anti-emetics (to combat nausea)
  • Muscle relaxants and anti-convulsant therapy
  • Analgesia for pain
  • Monitoring for hypertension and other vital parameters
  • Wound care
  • Miscellaneous Intensive Care

For severe cases (i.e. cats) there is a Black Widow Antivenin available. This therapy when appropriate can provide quick and effective relief of clinical signs in some cases. As with any medical situation response to treatment/therapy is individualized.

With most toxins that pets can become exposed to, prevention is an important and effective measure.  Helping your pet to avoid a venomous spider bite may be more challenging then protecting your pet from other hazards but there are still steps you can take to try and minimize the chance your pet will be bitten by one of these spiders.

If you are away from home keep your pet on a leash and don’t allow them to investigate any space that could provide spider habitat (holes, wood piles, debris piles, hay bales, basements, foundations, underneath window sills, under logs, etc.

At home, eliminating spider habitat is the most proactive prevention measure. Don’t allow your dog to roam free and keep his fenced in yard free of debris. Keep foundations, porches, swing sets, picnic tables, and under windowsills swept and clear of spider webs. As spiders can take up residence in the dark corners of your home, eliminating clutter and keeping spider webs cleared from corners, under cabinets, windowsills etc. can minimize interactions.

If you find a widow spider set up with her nest, consider finding a professional who can move her away from your home.

Remember, spiders are valuable insect killers and hold a useful place in your local ecosystem. The venom they possess is intended to kill the insects they eat. If you can avoid conflict by eliminating habitat opportunities in your home and directly around it, you can protect your pet from a dangerous medical incident while practicing “live and let live”.

If you have any questions about venomous spider exposure, we recommend contacting your veterinarian or Pet Poison Helpline®.



  1. https://extension.colostate.edu/docs/pubs/insect/05605.pdf
  2. Small Animal Toxicology 2nd edition (by Lynn Hovda, Ahna Brutlag, Robert Poppenga, Katherine Peterson.
  3. PPH Widow Spider Treatment Guideline
  4. PPH Black Widow Envenomation Page
  5. https://www.mexperience.com/three-spiders-to-be-mindful-of-in-mexico/
  6. https://www.canadiangeographic.ca/article/animal-facts-black-widow-spider
  7. https://www.stlzoo.org/animals/abouttheanimals/invertebrates/spidersandscorpions/blackwidow