Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

Let It Rain

added May 7, 2012

I first became aware of the problem back in 1980. I am sure of the year because it happened to coincide with the eruption of Mt. St. Helens in the state of Washington. I know that the two had nothing to do with each other, but in my mind they are forever linked. It happened this way:
The wedding reception was outdoors. In an oak forest. The tablecloths were white. For the moment. But soon they were covered with a black debris falling from the sky. A friend commented on how amazing it was that ash from the recently erupted Mt. St. Helens had traveled all the way across the country to fall on our wedding party. I, being more in tune to what was happening in the natural world, pointed out to our table mates that it wasn’t volcanic ash that was raining down upon us but caterpillar poop. And that was why I was covering my drink with my hand.
1980 was not the first big outbreak of the gypsy moth caterpillar. Just the first in my lifetime. The first big outbreak happened back in 1890.

Etienne Trouvelot fled France during the coup d’etat in 1852 and landed in Medford, MA. Trouvelot earned his living as an artist but was also an amateur entomologist. His main interest was in raising moths for their silk production. Our native silk moths are very good silk producers but rather difficult to raise in captivity because of their finicky eating habits. Trouvelot wanted to cross-breed them with a moth that would eat most everything. He hoped that the offspring would posses the silk production capabilities of the one and the ease of feeding of the other. So he imported some gypsy moth eggs from his native France.

Trouvelot’s cross-breeding experiments were a failure. The two moths were incapable of breeding. But he was right about one thing. The gypsy moth will eat just about anything. They are known to feed on over 150 types of our native trees and shrubs.
The details are not well known, but sometime in the late 1860’s some of his gypsy moth caterpillars escaped. Trouvelot notified local entomologists of the potential problem, then gave up entomology for astronomy. He moved back to France about the time of the first moth outbreak on his street in Medford.

By 1890, the problem had become so great that the Mass State Board of Agriculture started a program to eradicate the moth. And we have been fighting, and losing, the battle ever since. For a while there was hope of a victory, until we realized the damage DDT was doing to the environment was much worse than the damage caused by the gypsy moth. When DDT was banned in the early 70’s, the gypsy moth staged a comeback. Leading us to the outbreak at the 1980 wedding.

Gypsy moths are here to stay. Most years, they are a minor nuisance. But every so often their population explodes. Each year for the next two or three years, their numbers increase until they become so numerous and destructive we wonder if any trees will survive to leaf out next year. Then the population crashes and our trees are spared til the next outbreak. These population crashes are usually caused by a virus, gypsy moth with viruscommonly called the “wilt disease”. Caterpillars with the wilt can be seen hanging from a branch by their middle in an inverted V shape. The wilt disease seems to affect the gypsy moths only when the populations reach titanic proportions. By the time the virus becomes active, the trees have already suffered a few years devastation by the moths. While I am very grateful for the work the virus does, what we need is something that will attack the caterpillars before their numbers reach epic proportions.

The summer of 2006 looked to be the beginning of another outbreak cycle. The numbers of caterpillars was on the rise again. I had been tediously picking caterpillars off a few of my favorite fruit trees in the hope of sparing them some of the damage. On some of the larger oak trees in the yard, I had wrapped a layer of Vaseline-coated aluminum foil around their trunk. Gypsy moth caterpillars will often descend to the ground on silken threads to hide in the leaf litter during the daylight hours to avoid predators. At night, they will crawl back up the trunk to resume their feeding. If they can’t get past the Vaseline barrier, they can’t feed on the leaves. I don’t know how effective this is, but at least I feel like I am doing something for the trees.
One morning I noticed about 50 caterpillars on the trunk of the tree just above the auminum foil. Not moving . Not climbing up or heading down. All hanging on to the trunk face-down. Puzzled by this strange behavior, I decided to investigate. What I discovered was all of the caterpillars were dead.

Somewhere around 1910, scientists released a fungus into forests around Boston. The fungus came from Japan and was known to infect Gypsy Moths. Their hope was the fungus would help to keep Gypsy Moths numbers in check. After being released, the fungus promptly disappeared from sight. gypsy moth with fungusThe next year, the scientists didn’t find any fungus in the gypsy moths. It remained hidden from sight until 1989. 1989 looked like the beginning of a large outbreak. The numbers of caterpillars that year were not large enough to trigger the virus, but things were headed that way. But that summer, the caterpillars stared to die from a mysterious disease – which, upon investigation, turned out to be the long-lost fungus. No one knows where the fungus has been for the last 96 years or why it suddenly appeared in 1989, but both 1989 and 2006 had very wet summers. And fungi love moisture.
So later this summer, when the gypsy moth caterpillars start feeding on my favorite trees, I will be praying for rain. Now if only someone would discover a fungus that liked mosquitoes…