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.

Hawthorn Cedar Rust - Follow-up

A few months ago I mentioned the Hawthorn Cedar Rust that was attacking the Dwarf Hawthorn, Crataegus uniflora. The rust has been very detrimental to many of the hawthorn fruits. Fruiting bodies have recently opened and deposited spores onto the leaf below. Fortunately for the hawthorn, these spores are only capable of infecting Eastern Red Cedar, the alternate host in the rust life cycle.

Leaves have also suffered from the attack of the rust. Brown patches and edges are the most evident results.

Twigs that showed rust damage in May have developed these hard growths. This is a rather odd looking growth and looks as though the plant was trying to defend itself by growing a woody barrier between itself and the rust. As a defense against fungal invaders, many plants will use this type of defense and the result is a canker or odd growth mass at the point of infection. Maybe I don’t have to be so worried about the Cedar Rust killing off these uncommon plants.

As a whole, the shrubs look healthy. Fruit production was low this year, but the plant itself doesn’t seem to have suffered.

A few small yellow spots are all that is left of the infection on most of the leaves.

There were even several healthy fruits produced. My visit to the Dwarf Hawthorns had me in a really good mood. That changed slightly when I pulled my arm back a little bit too far while taking this shot.

I felt leaves brushing the back of my arm and then there were a couple of pin pricks. At first I thought it was just those pesky ants trying to protect some food source they had found on the hawthorn leaves. I ignored it and went on with my picture taking, until a wash of hot prickles started to spread from my elbow to my shoulder. I had managed push against this innocent looking mass of fluff, commonly known as a Flannel Moth larva. Beneath the fluff is a collection of poisoned spines that produces an effect similar to stinging nettles. As I type this, about 12 hours after the encounter, my arm is still sore and I have a nice red welt. At least I now know how I react to this particular poison. It probably wouldn’t have been this bad if I’d had the sense to pull away at the first sting.

Hawthorn Cedar Rust

It’s bloom time for the Dwarf Hawthorn, Crataegus uniflora, so I made a point of getting out to look at it yesterday. There were several blooms along with some unopened buds and developing fruit.

The plants looked in good shape. The leaves were a dark glossy green and there was very little dead wood in the plants. Dwarf Hawthorn is rare in Ohio, so I monitor it closely through the year.

I saw a bud with some yellow bumps and since the yellow spots were being tended by an ant, thought they were probably yellow aphids. A closer examination proved that assumption to be false. The yellow bumps were a deformity on the plant itself.

A second bud showed the same spotting. At this point I suspected the plants were displaying signs of Hawthorn Cedar Rust, a fungus with a life cycle like the Apple Cedar Rust I talked about a few weeks ago. However, HCR is most commonly found on the stems and leaves and those looked fine.

Well, maybe they’re not as fine as I first thought. Here are some signs on the stem and the leaves are showing just a hint of spotting. The yellow eruptions are the site of spore release for the fungus. There must also be something present that is of value to the ants.

Here’s a leaf showing development of the fungus galls. Other species of Hawthorn at Blue Jay Barrens display signs of the fungus every year and manage to survive and grow. It’s extremely disappointing to have such a rare plant infected with the disease. Maybe it’s the unusually wet spring that is to blame for this infection and things will get back to normal the next dry year. I’ll just have to watch and see what happens.