Are Large Yellow Underwing Caterpillar Poisonous?

Large yellow underwing moths are beautiful creatures with bright, flashy wings but are large yellow underwing caterpillar poisonous? Should you let them sit on your plants? Let’s find out. Notorious for the damage they cause to plants, caterpillars are a nuisance you should tend to immediately if they are in your garden. Some caterpillar species … Read more

Do Underwing Caterpillars Bite? A Friendly Guide to Their Behavior

Underwing caterpillars are often a topic of curiosity, particularly when it comes to whether or not they bite. These intriguing creatures are the larval stage of underwing moths, known for their striking wing patterns and colors. It’s important to note that underwing caterpillars, like other caterpillars, do not have the ability to bite or sting … Read more

Copper Underwing Caterpillar or Humped Green Fruitworm

In this article, we share information on the copper underwing caterpillar Do you think of moths as boring, brown insects? Think again. Behind those boring brown wings, you might find bright colors like red and orange!  Moreover, moths during their larval stage can be brightly colored caterpillars. The case in point is the Copper Underwing … Read more

Underwing Caterpillar – All You Need To Know

underwing caterpillar

Underwing moths are fascinatingly beautiful creatures, but what about their caterpillars? Are underwing caterpillars equally rich in colors and variety? Find out all this and more below! Underwing moths carry quite a unique appearance due to the heavily contrasting colors of their wings. However, they also happen to be plant-eating pests.  Regardless of whether you’re … Read more

Do Underwing Caterpillars Bite?

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.

Do Underwing Caterpillars Bite


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),
  • 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?


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?
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

Underwing Caterpillar

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!

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??
Austin, Texas, USA

Underwing Caterpillar with Parasitic Fly Larvae

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.

Read more