Flannel Moth Caterpillar: All You Need to Know for Safe Encounters

Flannel moth caterpillars, also known as puss caterpillars or asp caterpillars, are fascinating creatures with unique characteristics. These caterpillars are known for their distinct appearance, which includes thick, fluffy setae that resemble a pussycat’s fur, giving them the name “puss caterpillars” Puss Caterpillar.

In this article, we will explore various aspects of the flannel moth caterpillar, such as its life cycle, habitat, and interaction with the environment. As we delve further into these intriguing creatures, you’ll come to appreciate the complexities of their existence and their importance in the natural world. Some key points to remember about flannel moth caterpillars include:

Physical Characteristics

Size and Color

The flannel moth caterpillar, also known as Megalopyge opercularis, is recognizable by its distinct appearance. The caterpillar features:

  • A hairy texture that looks like soft fur
  • A gray, yellowish, or brownish color

Adult flannel moths are chunky-bodied, with their bodies, legs, and wings covered in fluffy hair, giving it a fluffy appearance 1(https://education.mdc.mo.gov/discover-nature/field-guide/flannel-moths).

Flannel Moth Caterpillar Adult Flannel Moth
Size Caterpillars can reach about 1¼ inches long 2(https://mdc.mo.gov/discover-nature/field-guide/flannel-moths)
Color Gray, yellowish, or brownish

Venomous Spines

Beneath their soft, fur-like appearance, flannel moth caterpillars possess venomous spines that can cause painful reactions. Contact with these spines may lead to symptoms such as:

  • Intense pain
  • Headache
  • Nausea
  • Swelling

It’s essential to exercise caution and avoid handling these caterpillars to prevent the harmful effects of their venomous spines.

Habitat and Distribution

The habitat of the flannel moth caterpillar, also known as the puss caterpillar, spans across various regions in North America. These caterpillars can be found in states like Texas, Florida, and Arkansas, as well as along the east coast.

During the summer and fall months, flannel moth caterpillars are more active and easier to spot. They typically inhabit trees and bushes in these areas, feeding on their host plants.

Some common host plants include:

  • Oak trees
  • Elm trees
  • Wild plum
  • Sycamore

In comparing the distribution of flannel moth caterpillars in various regions, we can observe the following distinctions:

State Frequency Peak Periods
Texas High Summer-Fall
Florida High Summer-Fall
Arkansas Moderate Summer-Fall
East Coast Moderate Summer-Fall

By understanding the habitat and distribution of flannel moth caterpillars, you can observe and appreciate these fascinating creatures in their natural environment. Just remember to be cautious, as their stinging hairs can cause painful reactions.

Life Cycle

Egg Stage

  • Megalopyge opercularis, also known as the southern flannel moth
  • Eggs laid in clusters

The female southern flannel moth lays her eggs in clusters on host plants. The eggs are small, round, and have a light-colored appearance.

Larval Stage

  • Venomous puss caterpillars
  • Densely covered with fine hairs

The larval stage of the flannel moth is the well-known puss caterpillar. These caterpillars have a teardrop shape and are densely covered with fine gray or tan hairs that taper into a tail. They have a distinctive crest of rusty hairs along their backs and tufts of whitish hairs on their sides.

Pupal Stage

  • Tough cocoons
  • Remain on host plants

The pupal stage takes place within a tough cocoon, which remains on the host plant even after the adult emerges. These cocoons provide protection for the developing flannel moths.

Adult Stage

  • Small, hairy moths
  • Wingspan of 1-1.5 inches

After emerging from the pupae, the adult southern flannel moths are small and hairy, with a wingspan measuring between 1 and 1.5 inches. The females are typically larger than the males. Their front wings are yellow, while their hind wings are creamy yellow. The moths’ bodies are covered with thick, fur-like hairs that are yellow to orange in color.

Diet and Damage

The flannel moth caterpillars, also known as puss caterpillars, primarily feed on a variety of plants and trees. Their diet includes oaks, deciduous trees, shrubs, and other leafy plants. These caterpillars are a species of concern due to their potential to cause damage to their host plants.

One reason for the damage caused is the caterpillars’ voracious appetite for leaves. They can strip a plant or tree of its foliage in a short period. This defoliation can weaken the host, making it susceptible to diseases and other pests.

Here’s a comparison of the trees and plants most commonly affected by flannel moth caterpillars:

Plant Type Susceptibility to Damage
Oaks High
Deciduous Trees Moderate
Shrubs Low

Some notable aspects of flannel moth caterpillars include:

  • They are covered in thick, fluffy fur-like setae
  • Their potent sting can cause pain and discomfort to humans
  • Adults, called flannel moths, are covered in wavy, flannel-like scales

Keep in mind that despite their destructive potential, flannel moth caterpillars play an essential role in the ecosystem, providing a source of food for predators like birds and other insects.

Stinging and Medical Implications

Symptoms and Risks

The sting of a flannel moth caterpillar can cause a range of symptoms, including:

  • Burning sensation at the site of the sting
  • Swelling and itching around the affected area
  • Development of a rash called erucism, which can be painful1
  • Nausea or abdominal pain in some cases

A more severe allergic reaction may occur in some individuals, presenting symptoms such as:

  • Difficulty breathing
  • Fever

In these cases, it is crucial to seek immediate medical attention.

Treatment and Care

Here are some recommendations for treating the sting of a flannel moth caterpillar:

  1. Remove any visible spine remnants by using adhesive tape on the affected area2.
  2. Apply a cold compress to reduce pain and swelling.
  3. Use over-the-counter antihistamines or corticosteroids to manage itching2.
  4. If symptoms worsen or persist, consult a physician for possible diagnosis of dermatitis or other complications.
Symptoms Treatment Options
Burning Cold compress, pain relievers
Swelling/Itching Cold compress, antihistamines, corticosteroids
Rash Consult a physician if severe
Difficulty breathing/Fever Seek immediate medical attention

Natural Predators

Puss caterpillars, also known as flannel moth caterpillars, have several natural predators. Despite their potent stings, some predators still feed on them.

  • Insects: Predatory bugs, such as lacewings and lady beetles, feed on flannel moth caterpillars in their early stages of development.

  • Spiders: These predators can catch caterpillars in their webs or hunt them down.

Here’s a brief comparison of these predators in relation to flannel moth caterpillars:

Predator Advantages Disadvantages
Insects Attack caterpillars in early stages of growth May not target fully grown caterpillars
Spiders Use webs to catch or actively hunt caterpillars Can be deterred by the caterpillar’s sting

In conclusion, flannel moth caterpillars may have a defense mechanism in their sting, but they are still susceptible to predation from insects and spiders in their natural habitat.


  1. The Sting of a White Flannel Moth Caterpillar (Norape ovina) 2

  2. Asps and Other Stinging Caterpillars – Insects in the City 2 3

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Flannel Moth Caterpillar


Unknown caterpillar from Peru
May 22, 2010
I found this caterpillar on a walk through the Peruvian Amazon. It was about 2.5-3 inches long. I tapped the branch it was on to try and collect it, but some of the hairs started coming off so I decided to just take a picture.
Quincemil, Peru 640-800m in SE Peru

Asp from Peru

Dear Clayton,
In North America, there is a group of caterpillars in the Flannel Moth family Megalopygidae (which is represented on BugGuide) that are commonly called Asps.  Asps, which are also known as Puss Caterpillars, are stinging caterpillars.  We suspect your specimen is closely related to the Southern Flannel Moth, Megalopyge opercularis which is profiled on BugGuide.

Letter 2 – Mysterious Brazilian Caterpillar


what’s that bug
Hello! My name is José Antônio. I live in Brazil. I found this caterpillar (Megalopygidae) in a orange tree. Can you help me to identify the species? Thank you very much.

Hi José Antônio,
Sorry to have taken so long, but we have tried to contact other people to get you an identification.  Sadly we are unable to help you.  You probably know much more about your native species than we do since you have identified it as a Megalopygidae.  Our members of that group are known as Puss Moths.  The caterpillars often have poison spines and are called Asps locally, especially in Texas.  Good luck with a positive identification.  Please keep us informed as to what you find out.  You can always raise the caterpillar since you know its food plant and then see what type of moth emerges.  Have a great day.  Daniel

Letter 3 – White Flannel Moth Caterpillar


white flannel moth caterpillar
I believe we found a White Flannel Moth Caterpillar while hiking the Cumberland Trail near Crossville, TN. One of our group got a bit of a sting when brushing past this colorful caterpillar. I would like to confirm the ID if possible.

Hi Millette,
You are absolutely correct. This is a White Flannel Moth Caterpillar,
Norape ovina, and the sting is quite painful.

Letter 4 – White Flannel Moth Caterpillar


identify caterpillar
My boyfriend found this caterpillar in his front yard in Southern Maryland. When he found this caterpillar(S) he was cutting the grass on a riding lawn mower and drove through a Red Bud Tree and out of the branches he started to get sensations in 3 or 4 spots on his body, on the side of his belly, arm and leg. Then there is a stinging burning sensation. We have searched the internet with no avail. Can you tell us what kind this is? Thanks
Steven & Sheree

Hi Steven and Sheree,
We did not recognize your caterpillar, and we were intrigued at your lack of luck in researching its identity. Searching the internet to no avail, in our minds, means that time and effort were spent. We simply typed caterpillar and redbud and googled, and the immediately found two sites, Stinging Caterpillars of Alabama, and Stinging Caterpillars on Shade and Ornamental Trees, that identified your caterpillar as a White Flannel Moth Caterpillar, Norape ovina, whose primary host is the redbud tree.


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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7 thoughts on “Flannel Moth Caterpillar: All You Need to Know for Safe Encounters”

  1. amazing photo of Asp.I took a photo of caterpillars on a tree near the border of Peru/Bolivia and would love to identify them but cant work out how to publish photo here?

  2. If you are stung by this caterpillar immediately smash it into the stung area . That will counteract the sting. Be sure to cover the caterpillar with a leaf or something as you smash it.

  3. From personal experience I speak. As a child I lived in South Texas and when an asp fell on me, the Mexican gardner smashed that thing into the area and it stopped the pain. What a relief. The man told us that they have always treated these stings in that manner so from university study I know that that bug has to have the antidote within its body. Do not touch the thing with your uncovered hand or it will sting you again,

    • We are not sure Cesar, except it is most likely a casualty of our site migration since it is a posting from 2003. We might be able to track down the original posting on our other computer. Thanks, but this is not a high priority for us right now since it involves a major amount of work to correct. Stay tuned for updates though.

    • Hi again Cesar,
      We located the old Dreamweaver file on this Brazilian Caterpillar and we have copied the original response to fill in the missing information. Thanks for bringing this to our attention.


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