Poisonous Caterpillars Can Sting Your Dog or Cat

Updated on August 30, 2019
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Stinging Caterpillars and Your Pets

Some caterpillars have a powerful sting, and it has happened that a curious dog or cat has been stung—sometimes seriously. This guide will help you know whether your pet has been stung by a caterpillar, and what to do about it if he has. Caterpillar stings do happen, and while they’re seldom an emergency, it’s good to know how to deal with it.

The best way to avoid exposing your dog or cat’s sensitive nose to a sting from one of the caterpillars described in this guide is to learn about the range, appearance, and food plants of these insects. This guide is a good place to start.

Can Caterpillars Really Sting?

The answer: Yes, some can. Many people don’t know that something as harmless-seeming as a caterpillar could pose a threat to their pet dog or cat.

Caterpillar stings are not produced by an actual stinger that pierces the skin, as with a bee or wasp. They also do not have teeth or fangs—caterpillar mouth parts are tiny, weak, and good only for chewing leaves.

Caterpillar stings are delivered by sharp spines or hairs on the insect's body. They can't fling or throw these hairs, so the only way you or your dog gets stung is by picking up the caterpillar or brushing against its stinging spines.

These defensive tactics are meant to deter predators and save the caterpillar from being eaten. Even though your pet isn’t a predator on caterpillars, these same poisonous spines or toxic juices that protect the caterpillar from birds and frogs can cause a problem for your dog or cat.

The spines of the buck moth caterpillar can give you and your pet a nasty sting
The spines of the buck moth caterpillar can give you and your pet a nasty sting | Source

Poisonous Spines and Your Pet

Having poisonous spines or hairs protects some caterpillars from predators like birds and frogs. Technically the term is “venomous,” since there is a substance in or on the spines that inflames tissue. Dogs and cats are not immune to caterpillar venom! Your dog’s nose is especially sensitive, and it’s also the part most likely to feel the sting of a venomous caterpillar. Just brushing against a venomous caterpillar can be enough to experience a truly painful sting.

The Asp Caterpillar, Megalopyge opercularis: The Asp caterpillar has the most intense sting of any North American species.
The Asp Caterpillar, Megalopyge opercularis: The Asp caterpillar has the most intense sting of any North American species.

Caterpillars That Could Sting Your Pet: The Asp

The caterpillar with the most painful sting, at least in North America, is a species known to science as Megalopyge opercularis. The common name, “the Asp,” is a reflection of the painful intensity of the sting—this is a caterpillar with the painful “bite” of a poisonous snake!

Of course, the Asp doesn’t bite (no caterpillars can actually bite, because their mouth parts are tiny and made for eating leaves). The way it delivers the venom is with sharp, stiff hairs hidden among the soft-looking “fur” that covers its body. It might look like a funny little hairpiece crawling along, but the pain of an Asp sting is no joke.

“A puss caterpillar sting feels like a bee sting, only worse. The pain immediately and rapidly gets worse after being stung, and can even make your bones hurt,”

— Don Hall, an entomologist at the University of Florida
Protect Your Pet From the Stinging Asp Caterpillar!
Protect Your Pet From the Stinging Asp Caterpillar!

Protecting Your Pets From the Asp

Your best weapon against an Asp sting is education—the more you know about this insect, the better you will be equipped to keep you and your pets safe. Check out the Asp distribution map (below) and it will tell you if you need to be concerned.

If you live in an area that has Asp caterpillars (sometimes the locals call them “puss moths" or "flannel moths"), stay alert for the period during late summer when they come down from the trees they feed on. At this time, they crawl around looking for a spot to pupate. Sometimes Asp caterpillars will take a shortcut and simply drop out of their tree, which is one way people and pets get stung—poisonous caterpillars raining down from the sky!

If you know about when this happens in your area, or you can ask, then you’ll have a small but meaningful head start on dealing with the risk that Asp caterpillars may pose to your pets.

Here's Where Your Risk of an Asp Sting Is the Highest
Here's Where Your Risk of an Asp Sting Is the Highest | Source

Symptoms of Caterpillar Envenomation in a Pet

  • Pet communicates pain; whimpers and whines
  • Licks, bites or paws affected area
  • Evidence of welts or swelling
  • Increased salivation
  • Increased heart rate
  • Loss of appetite
  • Changes in behavior; hiding; increased aggression (rarely)

Note that these stings do not leave spines or “stingers” in the victim, so these will not be evident in a caterpillar sting.

"If you have a pup that loves chasing bugs and happens to eat a stinging caterpillar, he may have a localized itching and swelling in the mouth and throat. In general, he is more likely to get stung on the nose. Veterinary treatment is usually antihistamines and steroids."

— Elaine MacKenzie, Canines and Caterpillars

What to Do If You Suspect Your Pet Has Been Stung by a Caterpillar

In general, caterpillar stings are painful but not a medical emergency. However, if you suspect your dog or cat has been stung, here are some considerations:

What to do if your pet (or you) is stung by a caterpillar:

  • Stay calm; this is not a life-or-death situation! Most caterpillar stings are mild and transient.
  • Wash the affected area with soap and water to remove any stinging hairs
  • You may consider applying topical sting relief; I have used Bearant Insect Afterbite for my own stings, and I trust it to work
  • Wait an hour or so. Nearly all caterpillar stings will fade away in this time
  • If possible, keep the caterpillar (or its remains) in a baggie. You may need it to show the vet.
  • If the sting does not fade, or your pet is in serious distress, do not hesitate to call the vet.
  • In rare cases, people and pets may have an allergic reaction to a sting. If this appears to be the case, especially if breathing is affected, call the Emergency Room immediately!

The Buck Moth Caterpillar, Genus Hemileuca: The rosette spines of the buck moth caterpillar could give your dog or cat a nasty sting
The Buck Moth Caterpillar, Genus Hemileuca: The rosette spines of the buck moth caterpillar could give your dog or cat a nasty sting | Source

Caterpillars That Could Sting Your Pet: The Buck Moth

After the Asp, the caterpillar most likely to sting your dog or cat is the buck moth. There are several species of buck moth occurring throughout North America, all in the genus Hemileuca. They all share many of the same basic characteristics.

Buck moth caterpillars can be very common and are often found in groups. One buck moth caterpillar can deliver a painful sting to a pet, but the risk is increased by the caterpillar’s tendency to gather together in groups, typically on the trunk of a tree. This is a behavior seen in other species, including non-venomous ones like the huge, striped caterpillar of Pseudosphinx tetrius. Often the entire mass of caterpillars will shake or quiver in unison, to appear to be one larger organism and scare away predators.

When buck moth caterpillars gather together on the trunk of a tree, they make a large mat of very poisonous caterpillars that you do not want to touch.

A Mass of Spined Caterpillars on a Tree Trunk
A Mass of Spined Caterpillars on a Tree Trunk | Source

Spines of the Buck Moth Caterpillar

One way to identify this species is by looking closely at the way the spines are arranged on the back. Buck moth caterpillars have many spines, some in sets of “rosettes." They are also typically large, plump caterpillars and occur in groups.

Buck Moth Caterpillars: What You Can Do

Especially if you live in the South, there’s a good chance that there are buck moth caterpillars somewhere in your area. They tend to go through population explosions, and this is when the risk of you pet being stung is greatest. Keep an eye out for groups of dark-colored, spiny caterpillars on oak trees and shrubs.

Be aware that these caterpillars, like all of the ones in this guide, are of course not just a hazard to your pets—you yourself can come away with a nasty set of stinging, burning welts from contact with these species!

Can Dogs and Cats Be Allergic to Stings?

The short answer is YES, according to petpoisonhelpline.com:

"Some pets, just like people, can develop severe systemic (anaphylactic) reactions to insect stings. In animals allergic to Hymenoptera venom, just one sting can cause anaphylaxis (a severe life-threatening allergic reaction)."

Hymenoptera is the insect order that includes bees, wasps, and ants, but in the case of some caterpillars, especially the Asp, it is possible to develop an anaphylactic reaction. It has occurred in people, and it's possible that it could occur in pets as well. If your pet shows any signs of difficulty with breathing following a sting of any kind, call your vet immediately—it could be a life-or-death emergency. (The same advice, of course, applies to people).

The Stinging Io Moth Caterpillar, Automeris Io
The Stinging Io Moth Caterpillar, Automeris Io | Source

Caterpillars That Could Sting Your Pet: The Io Moth

This species is related to the buck moth (above), even though it looks nothing like that species. Io moth caterpillars are typically bright green, with many pale spines and a red-and-white line running down each side. Also, unlike the buck moth, these caterpillars tend to be solitary, and are not really known to congregate in groups. They are large and hard to miss on the food plant (willow, maple, redbud, dogwood, and many others).

Unlike the buck moth, which is mostly a southern species, the io moth occurs throughout North America, with similar species stretching all the way into South America. One of the buck and io moth’s relatives has actually caused human fatalities! The sting of the Lonomia caterpillar can result in uncontrolled internal bleeding, and death has resulted in some cases. None of the North American species have this powerful venom, although if you know you are allergic to bee stings, you should exercise special caution around stinging caterpillars.

The amazing false eyespots of the adult Io moth.
The amazing false eyespots of the adult Io moth. | Source

Caterpillars That Could Sting Your Pet: The Saddleback Caterpillar

This species is mentioned in this guide simply because it stings and is very common, however, it is a small caterpillar, and unlikely to cause any real discomfort to you or your pets.

This is also a very interesting-looking, some might say beautiful, caterpillar; it belongs to a group of moth species, the family Limacodidae, that is known for having striking-looking larvae, all of which can sting to some degree. One of the insects in this group is the stinging rose caterpillar, which you might come across while gardening. Since they are small and seldom leave the food plant, your pet is unlikely to come across one.

The Remarkable Saddleback Caterpillar
The Remarkable Saddleback Caterpillar | Source

The One to Watch Out For: The Asp

Of all the species in this guide, this is the one to look out for. Most caterpillar stings are relatively mild and do not last long, but the sting of the Asp can be quite painful and can last for days in severe cases.

If your pet (or you) come into contact with one of these stinging caterpillars, it’s wise to call your local Urgent Care facility. At the very least, they can provide pain relief if necessary.

Watch Out for the Asp, AKA Southern Flannel Moth, Puss Moth
Watch Out for the Asp, AKA Southern Flannel Moth, Puss Moth | Source

Most Caterpillars Are Completely Harmless!

Finally, if you see your pet playing with a caterpillar, or there's an outbreak of them in your area, there is no need to panic! The vast majority of caterpillars are harmless to animals—in fact, there are only a handful that can sting at all. Being educated is your best line of defense against pet insect stings.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

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