Are Woolly Bear Caterpillars Poisonous? Helpful Facts

Woolly caterpillars are cuddly, and lots of people want to keep them as pets. But one question always comes up – are woolly bear caterpillars poisonous, like many others are? Let’s put all the fears at rest once and for all.

Caterpillars often make an appearance in kids’ storybooks as friendly worms. Yes, these insects are usually not aggressive and do not bite humans.

However, they are certainly not always something to be played with. In fact, some of the caterpillars can be so dangerous and poisonous that they can kill humans.

In this article, we will discuss the woolly bear caterpillar and find out if they are poisonous to humans and pets.

What Are Woolly Bear Caterpillars?

Woolly bears are caterpillars that grow up to be tiger moths. These caterpillars have fine and dense hair all over their bodies.

There are around eight or more types of caterpillar species in the United States that have such hair on their bodies and can be called woolly bears.

They are also known as banded woolly bears, fuzzy caterpillars, and more. These insects have black-colored bodies with rusty bands in the middle.

You can spot them in different regions of the U.S., southern Canada, and Mexico.

The chance of an encounter with a woolly bear caterpillar is highest during autumn, which is when they leave the food plants and shift into warmer spots to hibernate throughout the winter.

Are They Poisonous?

Wolly bears are not poisonous, and they are mostly harmless to people. These insects are not even aggressive, and they usually curl up like a ball to play dead when they feel threatened.

They lack a stinger and do not bite. However, if you touch them without any protection, there is a chance that the stinging hairs on their body can break into your skin, causing irritation and pain.

Other Poisonous Caterpillars

While the woolly bears are not poisonous, there are many other venomous caterpillars that can be lethal for humans. Here are a few of them:

Buck Moth

These caterpillars can grow up to 2 inches in length. They have a blackish-purple bodied topped with some bright yellow spots. Buck moth bodies are filled with sharp spikes that are harmful. You are likely most encounter them during the mid-summer season in willow trees.

Io Moth

Io moth caterpillars are green to yellow in color and have a red line bordering their body. They also can grow up to 2 inches in length and have black spikes all over the body. They usually eat plants like roses, corn, elm, oak, apple, clover, and more.

Puss Caterpillar

They show an average growth of an inch. A Puss caterpillar has a wooly coat of brown hair beneath which you will find a bunch of poisonous spikes that can cause problems like severe irritation in humans. You will find them feeding on trees like apples, maple, oak, and more.

Slug caterpillars

Slug caterpillars get their name from the habit of crawling around in leaves like a slug. If you look at them from above, you won’t be able to spot the head and legs. You are most likely to spot them crawling around leaves during the late summer.

Do They Bite or Sting?

Wolly caterpillars don’t have a stinger which is why they don’t bite humans. On top of that, they are not aggressive; if they feel threatened, they will curl up like a ball to play dead.

Do They Harm Humans or Pets in any way?

Although these insects don’t bite humans or pets since they are covered with fine hair, touching them without proper precautions can cause problems. The hair is strong enough to break past the human and cause severe irritation. Also, if your pet swallows one of these, the hair can get stuck in the throat, which will cause problems like allergies, gagging, coughing, and more.

Are They Dangerous to Plants?

The woolly bear caterpillars often feed on garden plants, flowers, and shrubbery.

They chew out big holes in these plants, and if a big group of caterpillar attack one plant, they can damage it to quite an extent.

On top of that, when they eat these plants, it decreases the aesthetic value of the garden flowers.

What Do They Turn Into?

The woolly bear caterpillar grows up to become an Isabella moth or a Giant Leopard moth, which is considered the largest tiger moth in the east. You will be surprised to know that it can take around 14 years for the eggs to turn into a complete moth for these species.

How Do They Survive Winters?

To survive the cold temperature in winter, the woolly bears search for warm places like rocks, fallen logs, and more to crawl into. They spend the entire winter hibernating in such spots.

There is folklore according to which these insects can be helpful in forecasting the weather.

If the brown band in their bodies is wide, there will be a comfortable and mild winter. However, if it is a completely black caterpillar, the upcoming winter will be harsh.

Frequently Asked Questions

Wrap Up

Woolly bear caterpillars are harmless to humans, but one should never try to handle these creatures recklessly.

The hair present in the body can cause problems like severe irritation. Also, if your pet swallows one, it will encounter problems like coughing and gagging.

Therefore always be cautious around these caterpillars. Thank you for reading the article.

Reader Emails

Many of our readers have asked over the years about the urticating spines of woolly bear caterpillars – these fuzzy hair are usually bad news because they cause allergic reactions and can sting you.

Do read the emails and our conversations about the caterpillars.

Letter 1 – Unknown Tiger Moth from Patagonia: Noctuid Moth

 

Arctiidae moth from Northeast Patagonia, Argentina
Hi Bugman!
I´ve found this beautiful and elegant moth several times since January, probably attracted by lights of a new building between the coastal dunes and the shrub vegetation (that we call "monte" in spanish) in Las Grutas, a beach city in Río Negro, Patagonia, Argentina. It is no longer than 2cm (0.8 inches). Hind wings have white and black broad lines and bloody red in the posterior area. All the femurs are shocking red too. I´ve been searching dozens of websites with Arctiidae pictures, but there are very few with southern South America´s ones. No luck until now… So I will try sending my low quality pictures (taken with a pocket cam) to you, in hope you can help me! Your site is one of my favourites, and I´m visiting it as much as I can to enjoy and learn with you and the people who write. I´m biologist, and had worked in spider taxonomy, but right now I´m working with shorebirds ecology. Your site keeps my loved and amazing bugs from all the world at hand! Thanks a lot for your work!
Mirta
in San Antonio Oeste and Las Grutas
Río Negro. Patagonia
Argentina



Hi Mirta,
Thank you so much for your touching letter. It is the first query we have ever received from Patagonia. Sadly, we cannot identify your lovely Tiger Moth, but we plan to post it for our readership. We will also contact our venerable neighbor, Julian Donahue, an expert in the Arctiidae, in the hopes that he can provide you with an answer.

Update: (03/10/2008)
Hi Daniel,
Got the photos, and have printed them. I won’t be able to give you an answer until I check my references at the Museum on my next visit … . However, I suspect that your moth is actually a noctuid, rather than an arctiid (although the higher classification nerds have recently demoted the arctiids to a subfamily of noctuids–what a blow!). Just didn’t want you to think I overlooked your query. All the best,
Julian

Letter 2 – Isabella Tiger Moth Caterpillar

 

Banded Wooly Bear Hello Daniel, I took a picture of this fellow on my lawn. Looked it up in my National Audubon Society “Field Guide to Insects & Spiders”. I actually don’t have much luck identifying bugs from this book… but occasionally I get lucky. In its description it stated… “According to superstition, the amount of black in the caterpillar’s bristle coating forecasts the severity of the coming winter. Actually, the coloration indicates how near the caterpillar is to full growth before autumn weather stimulates it to seek a winter shelter.” It doesn’t really explain how it overwinters, or where. Do they burrow underground? Cocoon themselves up? Thanks! Yvonne Barrie , Ontario Hi Yvonne, The Banded Woolly Bear is the caterpillar of the Isabella Tiger Moth. The caterpillar sheds its hairs forms a cocoon from the hairs. It pupates inside the hair shell.

Letter 3 – Milkweed Tiger Moth Caterpillar

 

i found this in my yard i have never seen one look like this. Its not a bad thing but i thought i was a really cool thing can you tell me what kind this is.. thanks for your time robert fell INDIANA Hi Robert, This is a Milkweed Tiger Moth Caterpillar, Euchaetias egle. It is also known as a Harlequin Caterpillar and it feeds on milkweed.

Letter 4 – Lophocampa Tiger Moth Caterpillar

 

What’s THIS Bug Hi Bug Experts, I work for a nature center just south of Durango Colorado, in pinyon-juniper habitat and river bottom. We sit at about 6,100 ft in elevation. It’s pretty dry if you are not right in the river bottom. This caterpillar, photo attached, was EVERYWHERE this spring from about mid April to mid May. We would literally go on nature walks with kids and have them keep track of how many they saw. The numbers were often between 30-50 in a short walk. The caterpillar, on close observation, was eating the yellow clover growing at the nature center (legume specialist?) in and around the sage (not right in the river bottom). Full size caterpillars were about 1 3/4 to 2 inches long. No distinguishing marks other than black with yellow spines. We don’t have a field guide detailed enough to figure it out (Insects of North America is way to broad, and butterfly web sites don’t have enough pic’s of caterpillars). Any ideas? Thanks, Jennifer Kleffner Lead Naturalist/Community Resources Coordinator Durango Nature Studies Durango CO The spring caterpillar is the tiger moth, Lophocampa ingens. This is one of the few caterpillars that can remain active throughout the winter, feeding on pinyon (sometimes other pines) when days are warm enough. They usually make conspicuous webs in the pines. Can’t say about the other caterpillar. Beats me. Probably something in the subfamily Arctiidae, based on its hairiness. However, it may be a Sonoran tent caterpillar, if it is feeding on oak. Whitney Cranshaw Hi Jennifer and Whitney, It seems Jennifer wrote to us both and Whitney got the answer first. We will still be posting your letter and identification. Your second photo is rather blurry and not easily identifiable.

Letter 5 – Milkweed Tiger Moth Caterpillar

 

What is it? We have found three or four of these caterpillars in our back yard here in Lima, Ohio. We have searched several web sites and feel that it is not exactly like the Spotted Tussock Moth caterpillar. This one has black spines as well as the white, and the orange on its back appears almost woven They have been happily munching away at our milkweed. Is it a variation of the Spotted Tussock, or something else? Thanks for any help you may provide. Sincerely, Cheryl and Earl Fisher P.S. Our granddaughter calls these critters ‘callipitters,’ which I find quite amusing! Hi Cheryl and Earl, This is a Milkweed Tiger Moth Caterpillar, Euchaetias egle. It is also called a Harlequin Caterpillar as well as a Milkweed Tussock Moth Caterpillar.

Letter 6 – Tiger Moth from Ecuador: Idalus species

 

moth identification October 11, 2009 This photo was taken in Ecuador in the cloud forest, I would really like to know what kind of moth it is. Thais Ecuador, Nanegal

Hi Thais, We will contact lepidopterist, Julian Donahue, an expert in the Arctiids, to see if he can provide the species name for this beautiful Tiger Moth. Identification by Julian Donahue It’s a tiger moth in the genus Idalus. There are quite a few species in the genus, and I can’t give you a species name without comparing the photo to specimens in the collection (and even then there’s a chance we don’t have it there with a name). It’s similar to photos of Idalus herois posted on the Web, but there are a number of very similar species, and details of the head are not visible in this photo. Julian

Letter 7 – Unknown Tiger Moth from India is really Owlet Moth

 

Please help with the identification Location:  India,Maharashtra State, Nagpur City August 6, 2010 9:16 am Hi. i came across WTB & found it to be very helpful.recently clicked the picture of a Moth in the garden of my house.have consulted a few people about the identity of lovely insect but could’nt get a confirmed id. can you please help me with the same. Regards, Abhishek Sagar (India)

Dear Abhishek, Before doing any research, we can tell you that this is some species of Tiger Moth in the subfamily Arctiinae.  We will continue to research a species name and we have requested assistance from an expert in the subfamily, Julian Donahue. Julian Donahue corrects the family Actually, I DO recognize it! I can’t give you a definitive name until late next week, after my next visit to the Museum–I have to check my Indian moth references there. For now, however, I can tell you that this moth has been a most interesting one to study. It doesn’t key out to Arctiidae, and is not included in older works on arctiids because it belongs to a group formerly known as the Hypsidae, and Afro-Asian-Australian group of moths. Currently, the moth is placed in the subfamily Aganainae of the Noctuidae (not an arctiid at all). The moth is usually placed in the genus Aganais, but the Natural History Museum (London) names list says that Aganais is a junior synonym of Asota (previously recognized as a separate genus). Online I found references to an african species, Aganais speciosa, which was given the common name “Specious Tiger Moth,” an incorrect translation, because “speciosa” means “beautiful,” not “specious”! Seems like a few dozen species (at least) have been described in the genus, so it might help to know just what part of India the moth came from. I’ll let you know later next week what I come up with for a better name. Julian P. Donahue BTW, I forgot to mention that the larvae feed on Ficus, presumably making the larva and subsequent moth distasteful to predators. Julian P. Donahue Additional Update from Julian Donahue August 12, 2010 Daniel, I checked the literature at the Museum today. The moth in question appears in most of the older literature (and perhaps current online resources) as Aganais ficus (Noctuidae: Aganainae). According to the Natural History Museum (London), the correct current name should be Asota ficus. Appropriately named, as the larva feeds on Ficus. The moth occurs throughout India and Sri Lanka. It is distinctive in the Indian fauna: any other species of Asota in India will lack the black and white bars at the base of the forewing leading edge. Julian P. Donahue

Letter 8 – Which Tiger Moth???

 

Subject: Beautiful Snow Prince Location: San Francisco Bay Area, CA April 1, 2016 11:22 pm Hello Bugman! You answered an email I sent before about a moth, and so I thought I would ask again. I found this beauty while visiting my parents in the SF Bay Area. What kind of moth is he/she? It was such a beautiful creature. 🙂 Thanks for your help. You’re awesome! Signature: Claire

Dear Claire, This lovely moth is a Vestal Tiger Moth, Spilosoma vestalis, and according to BugGuide:  “Larvae feed on leaves of various flowering trees, particularly oak.”  We believe this may be the first example of this species on our site. That’s exciting! Thanks again, it made my day seeing the post on Facebook! ? Glad to contribute to moth documentation! Claire Update:  April 16, 2018 Thanks to a comment by Karoline, we are now wondering if this might be a Fall Webworm moth.

Letter 9 – Clio Tiger Moth Caterpillar

 

Subject: Caterpillar Location: Tucson April 1, 2017 11:03 pm Can you tell me what he is or what he eats? Found on a sidewalk. Signature: Brenna

Dear Brenna, Your image is quite amusing.  It appears you have been offering this Clio Tiger Moth Caterpillar, Ectypia clio, every imaginable vegetable except its preferred food.  According to BugGuide:  “Larvae feed on milkweed (Asclepias, Asclepiadaceae) and dogbane (Apocynum, Apocynaceae). Behr reported them on spreading dogbane (Apocynum androsaemifolium).”  It is also possible that this individual has left its food plant in search of a place to pupate, in which case it is no longer interested in eating. Thx. And you are correct. I will get him a stick unless he buries. That would explain why he was on a sidewalk.

Letter 10 – Wasp-Mimic Diurnal Tiger Moth from Thailand: Amata sperbius

 

Subject: Insect I.D Needed Geographic location of the bug:  Chiangmai Province, Thailand Date: 02/14/2018 Time: 04:04 AM EDT Your letter to the bugman:  Hello Bugman, I found this insect walking along some gravel on the side of the road.  It appeared to be injured and it could not fly.  Could you please help me identify this species. Sincerely, How you want your letter signed:  Myles Davis

Dear Myles, This beautiful wasp-mimic, diurnal Tiger Moth is Amata sperbius based on the resemblance of your individual to those pictured on iNaturalist and on FlickR.  Perhaps it is recently eclosed and its wings are not yet capable of flight.