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.
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.
