Underwing caterpillars are the larvae of underwing moths. While the moths have beautiful underwings like butterflies, their larvae are garden pests. But they don’t bite humans. Let’s learn more about these enigmatic creatures.
Underwing moths (Catocala) are from the Holarctic genus of moths from the Erebidae family and belong to the Lepidoptera order of insects.
The word Catocala comes from the Greek word Kato, meaning behind, and Kalos meaning beautiful, a reference to their beautiful and hidden underwings. It is pronounced, “kah-TAH-kuh-luh.”
Larger than most moths, they can measure anywhere between 2 to 4 inches. Their dull-colored front wings act as excellent camouflage when they rest amidst trees, but their red or yellow-colored hind wings are what make them so attractive.
What Are Underwing Moths?
There are about 200 species of underwing moths in the world. Nearly half of these are found in North America, while the rest are across Eurasia.
Of the Catocalinae tribe members, underwings are the rare few moths that birds and other predators eat.
Entomologists believe that whenever the underwing moth detects danger, it flies away quickly, displaying its multi-colored underwings with concentric black circles.
These circles look like the eyes of a large predator, which confuses and frightens the bird or rodent, giving the moth enough time to escape.
Some of the most common Underwing moths are
- Catocala gracelis,
- Catocala lacrymosa,
- Catocala. palaeogama,
- Catocala herodias,
- Catocala gracias etc.
Interestingly, each of these underwing moths has English names that are translations of very feminine greek words.
For example, Lacrymosa translates to tearful in English, while Gracelis means graceful.
What Are They Like?
First discovered by Peter Cramer in 1776, the underwing moths live in large numbers in the majority of the coniferous and deciduous forests of North America.
These moths are nocturnal insects and are harmless to humans, animals, and birds. They generally feed on nectar and sap.
However, their large size combined with the bright-hued underwings often scares people.
The adult moth predominantly flies after sunset, feeding on hickory, walnut tree sap, and nectar.
Many species of underwing moths have distinctive colors; they don’t look alike. Adult moths are pollinators.
They have smooth brown to gray colored forewings that have bright colors and hindwings that generally remain overlapped.
The female and the male moths are easy to distinguish. The female adults have bigger and bolder markings than the males that may or may not change over time.
Adult female underwing moths lay their eggs in clusters during summer months along the crevices and creeks in tree trunks. The eggs are pale yellow and turn darker with time.
The larval stage of the moth species is called cutworms. These larvae feed voraciously by chewing through the stems of plants, especially seedlings.
The soft-bodied worms can grow up to 1-inch in length. They have distinctive circular strips on their body. Their body consists of 4 distinctive sections, as described in the Owlet Caterpillars of Eastern North America:
- Lobe (the front),
- Saddle (middle), and
- Ridge (the behind).
They have thick setae on the belly, which have sub-ventral fringes, also known as rootlet setae.
Underwing caterpillars are called semi-loopers as they can coil their body into a C shape while moving. Smooth-skinned, these long and slender caterpillars have three pairs of abdominal prolegs.
Can They Bite?
There is no evidence directly stating that caterpillars bite humans. However, in some instances, they have been known to sting cats and dogs that might probe them out of curiosity.
Even though their bite is not poisonous, it can cause temporary swelling and discomfort.
Are They Dangerous to Humans?
Though the adult moths are harmless pollinators who feed on tree sap and nectar, the larvae can cause significant damage to human crops.
These caterpillars cause extreme damage to foliage by eating them away very rapidly. They chew the stems and cut through the base causing permanent damage.
They also damage the roots of plants and, in severe cases, cause permanent death. So while they don’t bite or sting, they can cost you your pretty garden plants or crops.
What Are They Attracted To?
The quote “like a moth to a flame” perfectly describes what Underwing moths are attracted to.
Though there is no concrete explanation for this phenomenon, underwing moths are nocturnal insects attracted to lights.
This also includes being attracted to UV lights invisible to the naked eye. This is why you might see them entering homes at night.
One of the most common baits used to trap underwing moths is by painting barks of trees with sticky traps and placing a light source nearby.
Where Do They Live?
Underwing moths live mostly in deciduous and coniferous forests, where there is an abundance of foliage to feed on all year long.
Adult moths also live in caves, under ledges, cliffs, rocks, and even drying leaves littered on the ground. The caterpillars feed extensively on the canopies, commonly seen hidden amidst bark crevices and tree gaps.
How Do They Camouflage Themselves?
Since Underwing moths are nocturnal insects, you might often see them hanging from tree barks in an upside-down position with open wings.
Due to the unique patterns, the wings allow them to blend seamlessly with the surroundings and keep them hidden in plain sight. Their distinctive gray and brown pattern conceals them among tree marks and drying foliage.
Caterpillars are constantly feeding during the entire day. Hence they are commonly seen on the stems and leaves.
However, they are masters at hiding in plain sight because of their distinctive color and boy striation. The larvae can easily be in plain sight yet blend in with the tree bark.
Frequently Asked Questions
What happens if a caterpillar bites you?
Caterpillars are not venomous and do not have any harmful effects, even if they bite humans. In case of an accidental bite, they might leave a slight localized skin irritation. But it usually fades away within an hour.
However, a puss moth caterpillar’s sting has venom in it, and it leaves behind hairs on the skin that can cause a severe burning sensation and rash. You will need to get medical attention immediately if one bites you.
Do caterpillars bite humans?
Most caterpillars do not have appendages or mouthparts strong enough to penetrate the skin.
However, some species have a hairy body, and these hairs can cause irritation, rashes, and burning sensation if they come in contact with the skin or other exposed areas of the body.
What do underwing caterpillars eat?
Underwing caterpillars are also known as cutworms because they cut the steam of plants. They can rapidly eat through stems, leaves, and even roots. Being in the larval stage, they are constantly in a feeding frenzy.
What’s the most poisonous Caterpillar?
The most poisonous stinging caterpillar responsible for numerous deaths is the Lonomia obliqua. It is one of the most venomous caterpillar species to have been discovered yet and has caused the deaths of many people in Brazil.
Know When It’s Time to Say Goodbye
While adult underwing moths are magnificent, they are a nuisance for trees and shrubs in their larval stage.
If you see them around your garden, it is best to eradicate them before it’s too late. Apart from being pests, they can also bite you, though the bite won’t cause much harm.
Thank you for reading!
Letter 1 – Possibly Underwing Caterpillar
found when cleaning out old mulch Found this guy amongst oak leaves, pine bark and acorns. He was slow, but alive and — well, I guess you can’t really say he was kicking…. Any ideas? Kay Valdosta, Georgia,USA Hi Kay, We haven’t finished researching yet. We believe this might be one of the Underwing Moth Caterpillars in the genus Catocala. They feed on a variety of deciduous tree leaves. There is a close match on BugGuide and a second equally close match.
Letter 2 – Underwing Caterpillar
what is this caterpiller? Is this a geometridae? If not, any ideas as to what it is? Ideas appreciated. Mary Kay Stewart San Antonio, Texas Hi there Mary Kay, This looks to us like an Underwing Moth Caterpillar in the genus Catocala.
Letter 3 – Underwing Caterpillar
Grey knobby, hairless caterpillar found in GA mountains April 25, 2010 Hello. My children found this caterpillar one evening after dark in the north GA mountains. It is about 1.5 to 2 inches long, and as big around as a pencil at its widest point. Any idea what this guy is, and or what he will become? Thank you so much North GA mountains We are confident that this the the caterpillar of an Underwing Moth in the genus Catocala, and you may compare your photo to an image from North Carolina posted on BugGuide. Underwing Moths get their names because they are masters of camouflage with upper wings that allow the moth to blend into the bark of a tree when it alights. The underwings are often brightly marked with red and orange stripes, and when the moth is flying, it is rather flashy, but upon alighting, the bright colors are hidden and the predator easily overlooks the resting moth. Thank you so much! My kids will be thrilled to know what it is! Mandy
Letter 4 – Double Mystery: Possibly Underwing Caterpillar with Parasitic Fly Larvae
What insects are on this caterpillar? April 27, 2010 I saw this caterpillar holding onto a cedar beam of the arbor above my deck. I’m curious if the insects piled up on this caterpillar are parasites or progeny. Could they be a symbiotic species?? Don Austin, Texas, USA Dear Don, This double mystery is one of the most unusual submissions we have ever received, but we have a couple of guesses and a theory. The caterpillar looks like an Underwing Caterpillar in the genus Catocala, and they are well represented on BugGuide. If not an Underwing Caterpillar, perhaps a related species like a Black Witch Caterpillar, also pictured on Bugguide. The hitch-hikers are definitely not progeny, and they are not acting like parasites, though parasites might be a possibility. The passengers look like fly larvae to us, possibly Syrphid Fly Larvae, though the behavior is most unusual. Might we fathom a crazy guess and suppose that the fly larvae are taking advantage of the mobility of the caterpillar to transport the larvae to a food source? This behavior is known as phoresy, and it is common in the world of arthropods. We would really love a professional opinion on this phenomenon. We will contact Eric Eaton and our friends at the Natural History Museum of Los Angeles County for assistance. Awesome. I thank you very much for your obvious passion. My brother and I have been inquisitive about nature since we hatched. He and I both marvel at the macro world that most don’t take the time to uncover. Now that film and processing is so cheap (digital photography ) we try never to waste a photo op in this world that gives us back aches to expose. Now that I have discovered your site, I will take advantage of your expertise, in situations whose mysteries evade my browsing abilities. Heartfelt thanks for your help, Don Soderberg South Mountain Reptiles Eric Eaton provides a partial identification Hi, Daniel: Ok, I’m not sure of the identity of the caterpillar, but the other larvae are erupting from inside of it. They are most likely larvae of a braconid wasp (family Braconidae). That synchronous emergence, from one exit hole in the host, is not uncommon. They will spin cocoons in a mass, too. Eric P.S. Might I have permission to blog about this, using those two images? Hi Eric, What’s That Bug? would grant you permission to use anything since we know it will be for educational purposes. We hope Don agrees. No problem using the pix. Wish I’d stuck them into a container that would have been suitable for all this to unfold. I’m sure I would have gotten the temps and humidity wrong, so . . . oh well. Brian Brown thinks they look like Fly Larvae April 29, 2010 They look like fly larvae to me. I asked Mike Sharkey, a braconid expert, to look at this, and he said “They do not look like bracs or any Hym to me. With the sharp posteriors they look like dips to me. Very interesting.” They don’t look like syrphid larvae; more like phorids, the group I work on. Many are parasitoids. Did Don collect any specimens or try to rear these out? Brian Brown LACM Entomology Thanks Brian, We will write back to Don to see if he kept specimens.
Letter 5 – Underwing Caterpillar
caterpillar ID please Location: Charlottesville Virginia January 21, 2011 12:02 pm I’m stumped on this one; it was found under leafy matter by my daughter last April. Is there a significance to the underside coloring? Thanks in advance. Signature: John Hi John, This it the caterpillar of an Underwing Moth in the genus Catocala. Quite fortuitously, BugGuide has a posting that shows both the dorsal view and underside of a similar Underwing Caterpillar.
Letter 6 – Underwing Caterpillar
What kind of caterpillar? Location: Summerville, South Carolina. Found him on the tree in the picture April 5, 2011 5:12 pm I was outside on the phone when I saw this guy on the tree. He blended in so perfectly I actually thought it was a little niche in the tree at first. After I got off the phone I picked up a stick and scooted him (her?) onto it. It has a purple with black horizontal lines on it’s underbelly. I would like to know what kind of bug it is, please. Signature: Caterpillar Fangirl Dear Caterpillar Fangirl, We believe this is an Underwing Caterpillar in the genus Catocala. That was our suspicion even before we considered your description of the purple and black striped underbelly which must resemble this image of an Underwing Caterpillar on BugGuide. Your photo nicely illustrates the camouflage ability of the caterpillar, but the adult moths are even more masterful at hiding. The upper wings of the adult moths in the genus Catocala are often colored like tree bark while the underwings are brightly colored. When flying, the Underwing Moth attracts attention, but it blends with its environment when it comes to rest. The hunter might still be searching for the bright red flying insect, but it is thwarted since the underwings are hidden when the moth is at rest.
Letter 7 – Underwing Caterpillar
caterpillar curiosity Location: central Indiana June 17, 2011 10:12 pm After checking several web guides, and making it to page 90 of your caterpillar submissions, I decided to try throwing myself on your mercy, O Mighty Bug People! I found this guy as I was attacking my seriously overgrown garden area, pruning down some tree-like plants (I have no idea what plants, sorry!). He blended in so well I nearly cut him in two when I was pruning. I’m located in central Indiana, and found him today, June 17. Any ideas what he might turn into? The closest photographic match I could find was a Malaysian Fruit Piercing Moth Caterpillar, which I have a hard time believing is here in Indiana. He’s 2 1/2 to 3 inches long. Signature: Cheers, Jamie Hi Jamie, Your Caterpillar will eventually transform into an Underwing Moth in the genus Catocala. They are masters of camouflage as both caterpillars and adults. You may compare your individual to this image on BugGuide.
Letter 8 – Underwing Caterpillar
Can you identify this brown caterpillar Location: South Texas March 22, 2012 3:28 pm We found this caterpillar on the side of our house. We have serched the internet and we can’t seem to find it. Signature: -MaKenna Dear MaKenna, We believe this is the caterpillar of an Underwing Moth in the genus Catocala. It looks very close to this image posted on BugGuide.
Letter 9 – Possibly Parasitized Underwing Caterpillar
Subject: Bug in backyard Location: Stafford Tx. USA April 24, 2013 12:06 pm I live in Stafford TX and found this critter in my yard on a piece of iron…what is it??? Should we run !!! Signature: Randy Dear Randy, This is a most curious set of photos, and we are requesting assistance from Eric Eaton prior to posting. This is a Caterpillar and we believe it might be an Underwing Caterpillar in the genus Catocala. They grow quite large. You can also compare your image to this photo of an Underwing Caterpillar on BugGuide. We are most curious about the surrounding objects. They look like the pupae of parasitic Wasps known as Braconids. The wasps are generally quite species specific. Here is a photo from our archive of a Hornworm parasitized by Braconids. The curious thing about your photo is that the pupae are not attached to the caterpillar. Again, we hope to get a more professional opinion for you. Daniel: I’m not an expert on caterpillars, but I think your scenario is right on. Definitely braconid pupae. This would be something interesting for Bugguide, and maybe someone else there knows more. As of yesterday I am now writing blogs (ghostwriting, actually) for The Blogger Pool for a major third party client in the pest control industry. So, I may not always get back to you as quickly as usual. Plus, my wife and I are visiting her family out of state May 5-13, just so you know I won’t be online very often then. Eric
Letter 10 – Underwing Caterpillar
Subject: What’s this bug? Location: Dallas, North Texas May 24, 2013 4:46 pm Hi! I live in Dallas and found this bug today. The underside of it is flesh colored with blood red spots and looks fleshy. It looks like a caterpillar of some sort. I live behind a wooded creek area and this was found near my pecan tree. Thanks for any info! Signature: Debra Hi Debra, We believe this is an Underwing Moth Caterpillar in the genus Catocala. Here is a photo from our archives and one from BugGuide with the “underside of it is flesh colored with blood red spots and looks fleshy” that you described.
Letter 11 – Underwing Caterpillar
Subject: large caterpillar Location: Troy, Texas May 26, 2014 8:30 pm This beautiful caterpillar (I assume) was on our tent late morning after camping overnight in a grassy area near a lot of pecan trees. Signature: Thank you, Lisa Hi Lisa, This looks like an Underwing Caterpillar from a moth in the genus Catocala. You can view some examples on BugGuide.
Letter 12 – Underwing Caterpillar
Subject: What is this creature? Location: New York May 30, 2015 9:04 pm This rather creepy looking caterpillar looking thing was crawling up my boyfriends back while we were sitting outside at 12 am in the morning. It appears to have pinchers on its back end(I think that’s its back end) and seriously moved around when poked with a stick. As though it was trying to get you with said pinchers. The underneath looked like a mixture of hole like suckers with red in them. Only way I can describe it is blood. It’s about 3ish inches long. Signature: Creeped Out Girlfriend Dear Creeped Out Girlfriend, We believe this is the Caterpillar of an Underwing Moth from the genus Catocala. We wish you had provided an image of the ” underneath looked like a mixture of hole like suckers with red in them.” Did it look like this image from The Backyard Arthropod Project? We just posted an image of our own native, adult Walnut Underwing from Southern California, but our image doesn’t show the beautiful, brightly colored underwings that give the Underwing its name. I wasn’t sure how to reply to this, so hopefully you’ll get this message, but that’s exactly what it is. Thank you so much!
Letter 13 – Possibly Underwing Caterpillar rescued from Pool in Arizona
Subject: Unidentified Caterpillar! Location: Southeastern Arizona April 1, 2016 10:55 am Dear bugman, I found a caterpillar in the pool this morning. He was still alive when I found him, so I took him in and gave him a few leaves from our backyard. We are still unsure what kind of caterpillar he is, or what he eats! Any help? Signature: Dawn S Dear Dawn, This might be an Underwing Caterpillar in the genus Catocala which is pictured on BugGuide, but we would not rule out any of the other groups in the superfamily Noctuiodea, which includes the Owlet Moths. We are tagging your submission with the Bug Humanitarian Award, and unless the caterpillar was dropped into the pool by a passing bird, we feel confident it was feeding on some plant in your yard. The plant upon which you photographed it looks like Mesquite, which is pictured on the National Park Service site, which leads us to believe it is a plant close to your pool. Try offering other leaves from your yard, and if it starts eating, you can place the caterpillar on that plant. Any additional information like size may help us to narrow down an identification. We also wondered if this might be a Black Witch Caterpillar, and according to Texas Butterfly Ranch: “Black Witch Moth caterpillars eat legumes, and favor acacia and mesquite. ” Update: The caterpillar created a cocoon out of silk. A few weeks later, he hatched into a common , brown moth. (about 1 inch long.) I released him and watched him fly away. Thanks for the Update. That was neither a Black Witch or an Underwing Moth, but our general ID from the superfamily Noctuiodea is still most likely correct.
Letter 14 – Underwing Caterpillar
Subject: Caterpillar? Location: Upstate New York May 26, 2016 5:44 am We found this under a tree. He is about 2 inches long. His underbelly is green with black spots. There are 2 black ‘spikes’ near his rear end. It is almost June here in Albany, NY. Signature: Abbie Donnelly Dear Abbie, We believe based on your image and descriptions that this is one of the Underwing Caterpillars in the genus Catocala, but we are unable to provide you with an exact species. You may browse through BugGuide to see some similar looking Caterpillars. Here is a BugGuide image showing a green underside with black spots.
Letter 15 – Underwing Caterpillar
Subject: What’s that bug Location: Montgomery, Alabama April 2, 2017 3:14 pm No horn or we would say it was a horned tomato worm Signature: Ellen Horton Dear Ellen, This is the Caterpillar of an Underwing moth in the genus Catocala. They blend in quite well when they are on lichen covered branches.