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.
Adults
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.
Caterpillars
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),
- Horn,
- 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?
Adults
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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