Caterpillars, the larvae of butterflies and moths, come in a wide variety of colors and sizes.
While most are harmless, there are a few species that can be poisonous or venomous, causing allergic reactions or painful stings upon contact with their hairs or spines.
One notorious example is the puss caterpillar, which looks innocent but has venomous barbs hidden beneath its hairy surface.
Touching this caterpillar can result in severe pain and discomfort that may last for days or even weeks.
Poisonous and Venomous Caterpillars
Caterpillar stings have increasingly become a public health concern globally.
It’s important to be aware of the potential risks associated with these creatures, especially for those spending time outdoors or in areas with high insect populations.
Identification of Venomous Species
Some caterpillars are both poisonous and venomous, using toxins for defense against predators1. A common example is the puss caterpillar.
Key identification features:
- Aposematic coloration (bright colors to warn predators)
- Presence of hairs, setae, or spines
- Unusual or unique shapes
Toxic Chemicals and Defense Mechanisms
Additionally, they may have urticating hairs, which release toxins upon contact5.
- Hemolymph (caterpillar “blood”)
- Setae or spines containing toxins
- Venom glands (may be associated with setae or spines)
- Urticating hairs (can cause itching and irritation)
Table comparing poisonous and venomous caterpillars
|Setae or spines
- Puss caterpillar: Venomous barbs
- Giant silkworm moth: Toxic caterpillar hairs
Common Poisonous Caterpillar Species
The Puss Caterpillar is considered the most dangerous caterpillar in the United States. Found mainly in the Southeast regions, it is also known as the Asp Caterpillar or Southern Flannel Moth Caterpillar.
Its spines can cause:
- Intense pain
- Burning sensation
Buck Moth Caterpillar
The Buck Moth Caterpillar is another species with venomous spines. When touched, they cause:
- Painful stinging sensation
- Reddened and irritated skin
Pine Processionary Caterpillar
The Pine Processionary Caterpillar is a problematic species found mostly in tropical climate zones. It can cause:
- Local dermatitis
- Systemic effects, sometimes life-threatening
American Dagger Moth Caterpillar
The American Dagger Moth Caterpillar is another painful stinger. Its bristles cause:
- Skin irritation
The Saddleback Caterpillar is a brightly colored, venomous caterpillar. Its urticating spines may cause:
- Intense pain
Table showing the impact of spines of different caterpillar species
|Intense pain, itching, burning sensation
|Buck Moth Caterpillar
|Painful stinging, skin irritation
|Pine Processionary Caterpillar
|Local dermatitis, systemic effects
|American Dagger Moth Caterpillar
|Skin irritation, rashes
|Urticating spines, venomous
|Intense pain, swelling
Caterpillar Bites and Human Reactions
Caterpillars, particularly the poisonous ones, can cause a range of symptoms upon contact with human skin. Some typical symptoms include:
- Rash: Itchy, red bumps may appear on the skin.
- Blisters: In some cases, small fluid-filled blisters can form.
- Burning sensations: A burning or stinging sensation may be felt.
- Allergic reaction: Some people may experience more severe reactions, such as shortness of breath or even anaphylaxis.
It is essential to know that not all caterpillars are harmful, and many are harmless to humans.
However, brightly colored caterpillars can be a warning sign of potential danger, as noted by entomologists.
Immediate First Aid Treatment
If you come in contact with a poisonous caterpillar, it’s crucial to take immediate action:
- Remove urticating hairs: Use adhesive tape to gently lift the caterpillar’s irritating hairs off the skin.
- Wash the area: Clean the affected area with soap and water to remove any remaining toxic chemicals.
- Apply ice pack: Place a cold pack on the skin to reduce pain and inflammation.
After initial first aid treatment, several long-term remedies can help alleviate the symptoms:
- Hydrocortisone cream: Apply an over-the-counter hydrocortisone cream to reduce itching.
- Baking soda: Mix baking soda with water to create a paste, and apply it to the rash to help soothe the skin.
- Oral antihistamine: Take an oral antihistamine to alleviate itching and prevent an allergic reaction.
Caterpillars, especially those in the poisonous category, can cause various symptoms upon contact with humans.
Knowing the symptoms and appropriate first aid treatments can help mitigate the effects and promote healing.
It is always a good idea to wear gloves when handling caterpillars or coming into contact with nature to avoid any unwanted reactions.
Environmental Interactions and Predators
Role in Nature
Caterpillars play an essential role in ecosystems as they serve as a food source for a variety of predators and help in the process of pollination.
Some caterpillar species can be poisonous, causing skin irritations or more severe reactions in humans when touched.
In Texas, for example, several venomous species such as the hickory tussock caterpillar, io moth caterpillar, white flannel moth caterpillar, and stinging rose caterpillar pose potential health hazards1.
A wide range of predators feed on caterpillars, including:
- Small mammals
- Insects like wasps and beetles
These predators help maintain a balance in the ecosystem by controlling caterpillar populations.
Some predators are selective, feeding on specific species like the Acharia stimulea or the Phobetron pithecium2.
Apart from their natural predators, caterpillars also rely on various defensive mechanisms to protect themselves. Some of these deterrents include:
- Camouflage: Many caterpillars blend in with their surroundings, such as leaves or branches of plants like willow, maple, and rose, to escape the attention of predators.
- Irritating hairs: Some caterpillars, like the giant silkworm moth, have irritating hairs that can cause a painful reaction when touched.
- Poisons: Species like the cinnabar moth and the monarch butterfly produce toxins in the larval stage, making them unpalatable or even dangerous when ingested.
Table showing different caterpillar species and their deterrents
|Hickory Tussock Caterpillar
|Eastern United States, Texas
|Io Moth Caterpillar
|Eastern United States, Texas
|White Flannel Moth
|Stinging Rose Caterpillar
|Eastern United States, Texas
|Eastern United States, Texas
|Eastern United States, Texas
Gardeners should be cautious when handling plants infested with caterpillars to avoid injury, and pet owners should keep dogs away from suspected venomous caterpillars.
The world of caterpillars looks fascinating, yet it presents potentially hazards.
While the majority of caterpillar species are harmless and play vital roles in ecosystems, some wield toxic defenses that can cause discomfort or severe reactions in humans.
Awareness and caution are paramount when encountering these creatures, particularly in regions with venomous varieties.
Understanding their identification, defensive mechanisms, and appropriate first aid measures can help us coexist with these unique creatures while minimizing any adverse impacts on our well-being.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about caterpillars. Scroll down to have a look at some of them.
Letter 1 – Red Caterpillar
Subject: red larva
Geographic location of the bug: Big Bend Nat. Park, TX
Time: 10:35 PM EDT
Seen on November 20, 2014 at about 6000 ft. on the Laguna Meadows trail. About 2 1/2 inches long and 1/2 inch in diameter. It looked like a gummy worm.
How you want your letter signed: Dusty
We are pretty confident that this is a Moth Caterpillar, possibly in the superfamily Noctuoidea, because it looks so similar to the caterpillars in the genus Heterocampa.
Here is a similar looking individual posted to BugGuide. We will continue to attempt a more specific identification. Perhaps one of our readers will have a suggestion.
Thanks very much, I have been wondering about what it might be for a couple of years.
You guys have the coolest site!
Letter 2 – Sparshalli Moth Caterpillar from Australia
Subject: Strange Caterpillar – Australia
Location: NSW Australia
September 10, 2013 8:02 pm
Came across this quirky looking caterpillar yesterday and have never seen one like this before.
I am in the Hawkesbury region of NSW, Australia.
The caterpillar is about 5cm long. Would love to know what he or she will eventually become.
I also have a video of him if you would like to see it, he is just adorable.
We did a quick scan of Butterfly House, but we didn’t have any luck identifying your caterpillar. We really must go to bed now. Perhaps one of our readers will be able to assist us in identifying your distinctive caterpillar.
Update: September 26, 2013
One of our readers supplied a comment indicating this might be the caterpillar of the Sparshalli Moth, Trichiocercus sparshalli, and based on photos on the Brisbane Insect Website and Butterfly House, we agree.
Letter 3 – Mystery Cocoons in Michigan
March 4, 2010
Following up – just to make sure – did you get the note and pics I sent of odd coccoons (1/2 inch, hundred of them, in Michigan) last week?
unsure if you got my first note
WE apologize sincerely. We did receive your first note, but alas, we had hoped to try to research your query prior to posting, but work interfered. We don’t know what these cocoons will metamorphose into. We will try to contact Eric Eaton to see if he recognizes the family at least.
We couldn’t even be certain that they are moths, but that would be our first guess.
Letter 4 – Entometa fervens, NOT Guava Moth Caterpillar
Strange caterpillar on Lemon-scented gum tree; SE Qld
Dear Daniel (I think that’s your name)
We found this caterpillar on a lemon-scented gum tree on our property this morning; thought it was a growth on the trunk until we looked closer and could actually see its legs. It seems to have attached itself onto the trunk and hasn’t moved for over two hours.
Questions are: 1. What is it? 2. Is it damaging the tree (which is only a young sapling)? 3. Should we leave it alone or remove it? I did look on your website but my computer is soooo slow I couldn’t open all the info you had on caterpillars. Hopefully this one is new to you so that I’m not wasting your time. My caterpillar (whatever it is) is on the move – but taken 24 hours to move about 4 inches. It is itself about 4 inches in length.
I’m looking forward to finding out what it is and have e-mailed all the people I think may have an idea of what it is, but so far no gel. Hope you can shed some light on what is probably a very common caterpillar. Many thanks
(02/03/2008) Strange caterpillar on Lemon-scented gum tree; SE Qld
Dear Daniel and Lisa?
So sorry – didn’t mention that my caterpillar is on our property in Warwick, South East Queensland, Australia. I’ve lived here for nearly three years and am amazed at how many bugs there are!
I’m having fun looking at your site, even if you don’t have time to answer my query. You might be interested to know that I found it by accident; all I did was type in “identify caterpillar Australia” and up popped your very informative and ‘pretty’ page. Hope I’m not being a pest e-mailing you yet again.
Heather from Warwick, Queensland
We have spent a goodly amount of time trying to identify your fascinating caterpillar, but to no avail.
We suspect it is in the superfamily Noctuoidea, family Noctuidae, the Owlet Moths or the or an Underwing Moth in the subfamily Catocolinae (family Erebidae). There are some taxonomical errors on the Caterpillars of Australian Moths website we tried searching. An American underwing caterpillar posted on BugGuide shares many similarities.
Breaking News: As we struggled with this posting, and trying to create all the links, we believe we have identified this caterpillar as a Guava Moth, Ophiusa disjungens, based on photos posted to the Geocities website.
Though many caterpillars in the Catocalinae group look similar, gum is listed as a food plant of the Guava Moth Caterpillar
Thank you for your prompt reply to my query (see below). However, I also received a reply from Don Herbison-Evans (whose website I found on your site, thank you) and he thinks it is Entometa fervens.
I had a look on the link, http://www.usyd.edu.au/museums/larvae/lasi/fervens.html and, sure enough, it is almost identical to my visitor. I took a video of the caterpillar last night and it had become very active indeed – I may have a new hobby!
Thanks for the update. We stand corrected.
Letter 5 – Moth Caterpillar from Nepal
Subject: Nepali Caterpillar
Location: Marchan Paradise View Resort, Nepal
January 24, 2014
While taking an early morning walk through the vegetable fields in a village near Marchan Paradise View Resort, I found this caterpillar. Please tell me what kind it is.
This is definitely a Moth Caterpillar and not a Butterfly Caterpillar. It resembles a Tiger Moth in the subfamily Arctiinae, and we found a similar looking North American species on BugGuide identified as being in the new world genus Apantesis. We will post your photo and attempt some additional research.
Letter 6 – Caterpillar on Marijuana Leaf in Hawaii
Subject: What is this?
June 7, 2016 2:11 pm
This appears to be a Caterpillar eating a Marijuana Leaf.
Yeah I’ve seen plenty of caterpillars eating cannabis flowers… I did not realize they also ate/attacked leaves.
Letter 7 – english grub
Can you identify a grub/larva whatever for me? I live in the south east of england and found two of these horrible things in my garden, or rather my dog did. They are about 3 inches long and fat, the head end of its body about 2 inches in circumference. It is greenish brown, and the most distinctive marking is on its head, it has markings like two large eyes.
It makes it look like a ‘pretty’ nursery rhyme sort of insect character. My dog found one is some bindweed undergrowth and the other on a fuchsia bush. Can you help me please. Havent had any luck from anyone else.
Thanks, Mary Thomas
It sounds like you have found some type of caterpillar, most probably a Swallowtail Butterfly or a Giant Silk Moth of some type. The eyelike markings are a defense mechanism to frighten birds, one of the greatest threats to a plump juicy caterpillar.
Here in the U.S. we have several Swallowtail Caterpillars that could possibly fit your description, including the Western Tiger Swallowtail and the Spicebrush Swallowtail. It is possible that you have a European species that has a similar looking caterpillar. Here are some images of Papilio troilus, the Spicebrush Swallowtail, I downloaded.
These look like nursery rhyme characters, and are frightful to birds. Unfortunately, they do not live in England and I can’t seem to find much information on your local fauna to give you a more accurate identification.
Letter 8 – Mexico Mystery
My family and I are living in Xalapa, Mexico for the year. We have many of these faux-bark creatures and I am fascinated! I have no idea what their classification is. I have tried desperately to find them on the Internet, but have so far found nothing.
They are about 1/2 inch long. They have a little caterpillar-like head but their bodies (shell?) look like bark. I have also found them going up and down webs or silk from the ceiling. They stick to the ceiling, plants or anything with their exposed mouths.
The one on my house plant is eating the leaves, but not too many, so I let him/her stay. Thanks for all you do!
Certain Inchworms in the Geometrid Family exhibit similar camoulfage tendencies. That is our best gues
Letter 9 – Mysterious Caterpillar Plague in Washington
Subject: green caterpillar
Location: NE corner of WA state.
June 27, 2017 1:53 pm
I’d like to identify the caterpiller (and it resulting moth or butterfly) in the attached photos. It seems to act like a tent caterpiller but spins a strand and drops down to earth. Most strands get wrapped around each other forming a much larger strand (1/4″ dia) that reaches the ground. This site was on a forest road in NE Washington.
Signature: John McMillan
Since it is green and appears to be hairless, this is most definitely NOT a Tent Caterpillar. Our web searching for caterpillars exhibiting this behavior in Washington has not produced anything significant, however we did find this interesting article Daily Mail concerning millions of green caterpillars on a single tree.
The site states: “Stuart Edmunds, from Shropshire Wildlife Trust, said he believed the moths could be the larvae of the aptly named ash moth: ‘It is incredibly rare, when there is a limited supply of trees like there is in this area the ash moth mothers could have decided to lay their eggs all in one place.
Usually the caterpillars would be distributed over many more trees and with this many on a few trees there is a danger it could weaken the trees'” Was the phenomena you observed limited to a single tree? We feel certain this is a moth caterpillar. Perhaps one of our readers will be able to help us solve this mystery.
Letter 10 – Mystery Caterpillar
American Copper Underwing?
Greetings from the “other” coast!
Hi Bug Man! We loooooove your site! Can you help with this one? My cat found this fellow in our yard today and my wife thinks it might be an American Copper Underwing caterpillar.
We have scanned through all the pages in your web site but couldn’t find this one. Our reference books don’t have very many caterpillar pictures so we’re not sure what it could be. I know you’re swamped with inquiries right now so we’ll understand if it takes a while before we see a response.
Keep up the amazing job with the web site! Cheers! Greg and Lori Ferens
Ingonish, Nova Scotia, Canada
Hi Greg and Lori,
We found images of the Copper Underwing Caterpillar, Amphipyra pyramidoides, on BugGuide, and that is not your species. For now, this will remain a mystery caterpillar on our site and hopefully someone will recognize it.
Letter 11 – Nawab Caterpillar from Singapore
Caterpillar with a crown?
Wed, Nov 12, 2008 at 6:22 AM
Hi, I found this caterpillar-like creature in a canal near my house. Can you help me to identify it? Thank you.
This is a Nawab Caterpillar from the genus Polyura. Information online indicates that there are only two species in Singapore. The caterpillar is not an exact match to the Blue Nawab, Polyura schreiber tisamenus, pictured on the Expert Insight website, but it looks even less like the Plain Nawab, Polyura hebe, also pictured on the Expert Insight website.
We also located a Polyura web page that indicates there are more species in Singapore, but we can’t locate images of the caterpillars. You will have to be satisfied with the genus Polyura and the common name Nawab Butterfly. In March 2008, we posted a photo of an Australian member of the genus, Polyura sempronius, and found that its common name is the Tailed Emperor.
Correction: December 18, 2008
Hello again, Daniel. a few other IDs and correction. Only two Nawabs ( Polyura ) presently fly in Singapore, both of which I am familiar with. This is a larval Blue Nawab ( P. schreiber ), which can be distinguished from the Plain Nawab ( P. hebe ) by its differently configured head horns and single — though at times absent, as here — dorsal crescent. I hope the above information is helpful.
Letter 12 – Moth Caterpillar from South Africa
Subject: Funny looking catterpilar
Location: Randfontein South Africa
November 29, 2014 6:04 am
Hi I just found this guy under attack by a bunch of ants, saved it and placed it on a strawberry leaf to photograph. (Don’t think that is the diet of this caterpillar)
The closest pic I could find on the net is of the one eyed sphinx moth from Alaska. This however is in Randfontein South Africa. Any ideas?
Signature: Vic Mouton
Though it has a caudal horn, we do not believe this is a Hornworm. We believe this is a Butterfly Caterpillar, not a moth caterpillar, and we believe it is in the Brush Footed Butterfly Nymphalidae.
We have not had any luck finding any matching images online, and we have contacted butterfly caterpillar specialist Keith Wolfe to see if he can identify your caterpillar.
Correction Courtesy of Keith Wolfe
Hi Daniel; I hope you had a wonderful Thanksgiving! This is definitely not a nymphalid (butterfly) larva of any sort, but rather an immature moth. Sorry to be of limited help.
Letter 13 – Parnip Webworm
Caterpillar “nesting” in closed Queen Anne’s Lace – not Black Swallowtail
September 17, 2009
Last week (Sept. 13, 3009), out of curiousity, I opened up some Queen Anne’s Lace “nests” – i.e., the closed cup-like shape that the blooms take as they go to seed. About 1/3 of the nests had one of these small caterpillars in it.
They were usually resting on or underneath a small silk pad, slightly larger than their bodies. The “nests” were full of frass, and it felt as if a bit of silk was being used to help keep the cup of the bloom closed more tightly than those without caterpillars inhabiting them.
All searches of “caterpillar, Queen Anne’s Lace” bring up the black swallowtail, but none of them seem to mention this caterpillar.
The closest I’ve come to identifying it is a picture of a Nettle-Tap Moth caterpillar. The Nettle-Tap Moth is found in England, which is the same place that Queen Anne’s Lace originated from, so it’s not impossible that that’s what this is. However, I can find no mention of it as a host plant. The nettle (of course) is what’s always mentioned.
This must be a fairly common caterpillar if it’s so easy to find. Can you help me identify it? Thank you.
I’m enclosing closeups of two caterpillars and one larger view which includes my thumbnail, for scale. The first caterpillar is smaller than the second, and may be an earlier instar.
Thank you for your wonderful site!!!
Lake Forest, IL
“Caterpillar “nesting” in Queen Anne’s Lace – NOT a Black Swallowtail
September 18, 2009
By searching “black spotted, caterpillar”, I found a caterpillar that has the same spot pattern my unknown one, but it can’t be right. It’s a Pickleworm (!). The only problem is that it’s a southern US caterpillar, and I live in Illinois.
Apparently they don’t survive cold winters and they like squash, canteloupe, and cucumbers. No mention of Queen Anne’s Lace, but they do tend to go for the blossoms of their food plants.
Wait, wait… in some years they may reach Michigan. Hmmm…
Here’s a link with info: http://entomology.ifas.ufl.edu/creatures/veg/pickleworm.htm
I’m attaching the photo that does resemble the caterpillar I found.
This is a Parsnip Webworm, Depressaria pastinacella, which you can see on BugGuide. We are not posting the found photo of the Pickleworm since you did not take it and since it is not your species.
Fantastic, and, considering the host plant, it makes a lot of sense. Great work, and thank you so very much!
I’m sorry, I didn’t expected you to print the photo I linked to; I was just including it in case it would help with the identification Thank you for your quick and perfect ID. Mystery solved!
Also, enjoying all the reactions to Ichneumons. I saw my first one last year during a bicycle ride in the woods, and it certainly freaked me out at first. Amazing that they can get those whip-thin ovipositors through the wood.
Many thanks from Illinois,
Update and Correction
Caterpillar “nesting” in closed Queen Anne’s Lace – not Parsnip Webworm either (Part III)
September 25, 2009
Turns out the caterpillar in question isn’t exactly a Parsnip Webworm (as it was identiied in the Sept. 19, 2009 posting).
I wrote to May Berenbaum, an entomologist at University of Illinois who studies Parsnip Webworms, to ask her why she didn’t have Queen Anne’s Lace listed as a host plant in her papers, since that’s what I found this caterpillar on.
Turns out there’s “a new moth in town”, so to speak.
Only recently identified as a newcomer to America, it is the Sitochroa Paelalis. Its larvae, of which there are few pics on the web (http://ukmoths.org.uk/show.php?id=3280), are only distinguishable from the Parsnip Webworm by experts, but the according to Dr. Berenbaum, the host plant and the time of year (most Parsnip Webworms finish their development by July, according to Dr. Berenbaum) help determine its identity.
Apparently it’s been spotted in Michigan, Indiana, and Illinois. I’ll try submitting some photos of the larvae to the bugguide to round out their collection, if they’ll take it (http://bugguide.net/index.php?q=search&keys=sitochroa+palealis).
I can’t thank you enough for this site and your help; I’d never have gotten to the right answer without you, and I’d never have gotten to write to a famous entomologist!
(p.s. You just know you’re begging for a smart aleck answer when you’re asked to prove your a human being by giving the color of snow! Didn’t you guys ever listen to Frank Zappa? *G*)
Lake Forest, IL
Letter 14 – Parsnip Webworm
The Parsnip Webworm: Nasty on Nasty
Didn’t see many webworms on your website, but I think I’ve correctly identified this one as a parsnip webworm?
I thought this volunteer plant in my yard might be yarrow (which I wanted), so I became obsessed with finding out what was destroying it with these yucky webs. Turns out my plant is Wild Parsnip, which can cause really bad reactions to people’s skin because of something called “furanocoumarins” that it secretes in order to try and ward off these darned parsnip webworms.
Seems it causes sunburn-like rashes and even blisters, along with a sensitivity to sun exposure. I couldn’t find any information about whether the worms have anything good about them, so I finally dunked the whole mess (plant and all) in soapy water. I’m not a bug killer by nature but had to get rid of the plant, so I hope I did the right thing.
This just seemed like nasty on nasty, am I right? Here are some pictures of what the nasty little webworms did to my nasty little parsnip, before I destroyed the whole thing.
p.s. Almost everything I found online talking about parsnip webworms or wild parsnip seemed to come from Illinois, which is where I happen to be. Made me wonder if they’re especially bad here, or something?
We really don’t care to pass any judgement regarding if you did the right thing or not, but we are very happy to have your letter and image to post.
This is a new species for our site and we are very happy you saved us what might have been hours of research to properly identify the Parsnip Webworm, Depressaria pastinacella. BugGuide has a few images that match yours and they provide a link to a site with more information.
Letter 15 – Probably Chrysalis of Common Rose: National Butterfly of Singapore
Subject: Caterpillar looks like bear
Location: Khon Sawan, Chaiyaphum, Thailand
December 10, 2016 5:09 am
Found this stuck to a vertical white wall outside our rural house in the shade of an air con unit, today 9th Dec 2016. It rolled up into this tight shape and stayed that way until we put it back and left it. Any ideas what this could be?
Signature: Thanks, Andrew
Thank you so much for including multiple view of different angles of this Chrysalis. After the caterpillar stage, butterflies and moths enter the pupal stage and the pupa of a butterfly is known as a Chrysalis.
We feel very confident that this is a Butterfly Chrysalis, and we suspect it is in the Brush Footed Butterfly family Nymphalidae. We will contact Keith Wolfe who is an expert in the early stages of development of butterflies to see if he recognizes the species.
Keith Wolfe supplies an identification:
Sawasdee Andrew and Daniel,
This is a Rose (Pachliopta) swallowtail chrysalis, most likely a Common Rose (P. aristolochiae) given its appearance and that species’ widespread abundance in Thailand. Here is more information from Singapore . . .
. . . where it outvoted five other candidates last year to become the national butterfly.