Clinical Signs of Spider Bites on Dogs

You’ll find a lot of worry and speculation about all kinds of harmful spiders online. But according to the CDC, there are only two groups of venomous spiders in the US that can cause serious harm for humans and pets: the Recluses (Loxosceles) and Widows (Latrodectus). Those two groups only account for 11 of the 3,000+ species in North America. And contrary to popular belief, they’re all far more scared of you and your pup than you might be of them.

The reality is that venomous spider bites are far less common than most people think. Most spider bites are a little red and itchy at worst. Slap a bit of soothing skin balm on those types of bites, and your pup will heal up as good as new.

But if a venomous spider bites your dog, he or she may need urgent medical treatment. Use this guide to learn about where venomous spiders live, how to spot them, and what to do if you think your dog was bitten.

Read our bug bite guide to learn more treating bites from mosquitoes, fleas, and other types of insects.

Clinical Signs of a Venomous Spider Bite in Dogs

Veterinarians rely on clinical signs to diagnose and treat venomous spider bite. If you observe any combination of these significant symptoms, call your vet immediately.

  • Seizures or tremors
  • Tissue necrosis at the bite center
  • “Drunk walking” or trouble walking or standing
  • Weak pulse (here’s a great guide to checking your dog’s pulse)
  • Respiratory collapse (extreme difficulty breathing)
  • Muscle cramps and rigidity
  • Abdomen (belly) sensitivity

Venomous spider bites might also cause fever, lethargy, vomiting, excessive drooling, and diarrhea. Those symptoms are also important, but they are most concerning when paired other major symptoms above.

Can a dog get sick from eating a spider?

No, your dog probably won’t become seriously ill from eating a spider — even if it’s a black widow. Why? Spiders are venomous, not poisonous. You cannot be poisoned by a spider.

Here’s a quick toxinology lesson. Poisons are toxic, which means they cause harm if swallowed or inhaled. Venoms, on the other hand, aren’t toxic unless injected into your bloodstream. That’s not to say venoms and other foreign materials (like grasshoppers, crickets, etc.) won’t give your pup a tummy ache. But the good news is that it’s highly unlikely eating any spider can do serious harm.

“…the spider is venomous, not poisonous. The venom causes problems when it is INJECTED into the body from a bite, but there is no evidence that swallowing a spider would cause any ill effects.” — Linda Erickson, AKA: The Spider Chick, Spider Ecologist

Widow Bites: Signs and Treatment

Black Widow bites become pretty painful right off the bat, along with redness and swelling. More severe symptoms can show up within just a few hours after the bite. In general, widow bites develop more rapidly and are much more painful than bites from a recluse.

Treatment and recovery: If veterinarians can identify the bite, they will administer antivenom. Pain medications, muscle relaxers, and supportive care are often required as well. Complete recovery can take several weeks, but fatalities are incredibly rare. (Before the antivenom was created, death occurred in less than 5% of human victims.)

An interesting fact: Black Widows’ mouths are so small that around 15% of bites are ‘dry bites,’ which means no venom was injected.

Recluse Bites: Signs and Treatment

Recluse bites often go completely unnoticed because they’re so painless. (If your dog yelps when bitten, it’s not a recluse.) Redness and stinging follow within the next 2-8 hours and a white blister might pop up in the bite site. Over the next few days that blister usually turns into a ‘bulls-eye’ lesion that ultimately turns into a dark area of dead tissue (necrosis).

Most Recluse bites cause a localized reaction — some never develop any serious symptoms. But on rare occasions, bites can induce a systemic reaction that’s much more serious. In addition to major symptoms like seizures and respiratory collapse, a systemic reaction may cause kidney problems and blood clotting.

Treatment and recovery: There is no antivenom for Recluse bites, but with treatment, they’re rarely ever fatal. Because Recluse bites cause severe tissue death (necrosis), a surgical procedure called debridement is often required to remove the dead tissue and infection. Healthy pups normally recover within one to three weeks.

Range and Location

Southern and Northeastern US is home for the nation’s two venomous spiders. Fortunately, there’s not much overlap between each spider’s range. So except for the southernmost areas in the Southwest, you’ll only have one of the two spiders to deal. If you live in the West and Midwest, you’re lucky — you’ll probably never encounter any of these spiders.

So before you assume the worst about a bump on your dog, take a look at these maps to whether venomous spiders might live in or near your area:

Recluse Range and Location in the US

Brown Recluse range and location in the US

Recluses live primarily in Southeast and Central Midwest.

Widow Range and Location in the US

Black Widow range and location in the US

Widows live primarily in the Southeast and Northeast.

Identifying Venomous Spiders

Widows (Latrodectus)

Brown and Black Widows are the most common type of Widow in the US. (Red Widows can be found in parts of Florida, but are rarely seen.) As the names imply, both species have a unique look. But what’s consistent is the hourglass marking on the abdomen. Adult widows are about a half-inch long.

Black widow spider

Habitat: Widows prefer dark secluded places. Woodpiles, outdoor sheds, closets, and other cobwebbed areas are prime habitats.

Recluses (Loxosceles)

The Brown Recluse (often called the ‘violin spider’) is the most widely know Recluse. But there are actually six Recluse species in total. Each type is a small spider that’s brown in color. Mature males share the famed violin-shaped mark on the head. Unfortunately, neither of those features truly help identify the spiders. To be a recluse, a spider must have all four of these features:

  • six eyes in dyads (pairs)
  • uniformly colored abdomen with fine hairs
  • uniformly colored legs with no spines
  • a body less than 3/8″ in length

Because of its generic color and features, the Brown Recluse is the most accused spider in the US. Rick Vetter, a previous staff research associate in the Entomology Department at the University of California Riverside, investigated data from 20,000 “brown recluses” submitted by worried Californians, but not a single one turned out to be recluse.

Brown recluse spider

Habitat: Recluses are nonaggressive spiders that are commonly found in quiet, undisturbed areas. Indoors, that could be your shoe, pantry, and anywhere that isn’t moist. Outside, they’re often found in sheds and woodpiles.

Recluses are incredibly true to their name. They’re so shy, in fact, can live alongside humans without ever crossing paths. For example, consider this study from the University of California Riverside. Researchers found over two thousand recluses(!) living in a Californian home and no one in the house had ever seen or was ever bitten by a spider. The moral of the story is that recluses must be agitated before they resort to biting.

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