Monday, September 19, 2011

Flannel Moth Caterpillar

This innocent looking bit of fluff fools a lot of people. Flannel Moth caterpillars can easily be mistaken for a wad of spider silk or an out of control fungus or a downy feather stuck to a tree branch. It’s hard to see that the body of a caterpillar is hidden within the wild mass of hairs.

Upon closer examination, you can detect the outline of a body and some vertical striping. A visual examination is as far as you want to go with this guy. Hidden within the hairs are stinging spines that can deliver a potent dose of an itching and burning toxin. The combination of disguise and pain provide the caterpillar will an effective defense.

It’s really hard to see the mouth, but if you watch for a while you’ll find the mouth at the point where the leaf is disappearing. The caterpillar begins feeding at the leaf tip and then eats back and forth across the leaf in a pattern similar to a person eating an ear of corn. This pattern maintains a distinct leaf shape to the uneaten portion. Many caterpillar predators detect their prey by investigating irregularities in the leaf being consumed. Keeping the leaf looking like a leaf helps to avoid notice by these predators. This caterpillar certainly employs a wide range of tactics in order to avoid predation.

At a distance, this certainly doesn’t seem to be a caterpillar. The shrub being consumed is a Dwarf Hawthorn, Crataegus uniflora. Dwarf Hawthorn is a rarity in Ohio. Flannel Moth caterpillars feed on a wide variety of trees and shrubs, but it’s on the Dwarf Hawthorn that they are regularly found.

Appearance of the caterpillars is always a late season event and doesn’t seem to cause any negative effects to the Hawthorn. The tiny shrubs have produced several fruits this year.

The Dwarf Hawthorn leaves look quite healthy. Quite a difference from last year when the leaves suffered from a bout of Hawthorn Cedar Rust. Fortunately, most native plants can handle quite a range of diseases and predators without being killed. Hopefully these rare plants will thrive and continue to produce my annual encounter with the Flannel Moth caterpillars.


  1. ...hmmm...I wonder if I've ever been fooled. I bet I have and simply walked on instead of taking a closer look. Loved this post. I'm going to keep my eyes open...

  2. Hi, Kelly. I imagine a lot of people dismiss these caterpillars when they see them. I guess that's better than accidentally getting stung. I backed into one of these last year and got a sting that kept my arm aching for over 12 hours.