Nine Minute Naturalist by Josh Palumbo
Allow Me to Introduce You
“Out of sight out of mind” is a familiar phrase that is easy to understand. If you do not see something or someone for years they get pushed back into the recesses of the brain until they become part of our life again. I believe spongy moth (formerly known as gypsy moth) falls perfectly in that category. This edition of the Nine Minute Naturalist will serve as a reintroduction to a familiar pest that brought distress to the forests of Wintergreen for decades.
Spongy moth is a non-native pest that was introduced to North America as an escapee from a lab in Massachusetts in 1869. It made its way to Virginia by the 1980s and was a nuisance for decades. The saving grace of our forest was the successful introduction of Entomophaga maimaiga, a fungal pathogen that hosts in the body of spongy moth caterpillars. April showers not only bring May flowers but it also creates a robust environment for Entomophaga maimaiga to grow and act as a control agent. The past few years have brought warm dry Aprils that have not helped fungal growth and in turn has greatly aided spongy moth resurgence.
This resurgence is on display this year as we are experiencing our first defoliation since the spring of 2012. Our western boundary is experiencing winter-like conditions as many trees are bare as the caterpillars strip the leaves off the trees. The caterpillar levels are high enough to produce effects such as frass raining down and caterpillars “ballooning.” Frass is a fancy word for caterpillar excrement. When the levels get high enough to defoliate trees, the frass sounds almost like a light rain coming through the canopy. When the caterpillars begin to run out of leaves on one tree they will “balloon” which means they will dangle in mid-air from a silky strand waiting for the wind to blow them to another food source.
The preferred food source of spongy moth is our beloved oak trees but they are content to feed on hickory, maple, birch, beech and a variety of others which call our forest home. Defoliation is not a death sentence for trees but it can be a problem in the long term. If a tree is healthy, they will flush out a new set of leaves. Defoliation is problem for trees already stressed and those trees may struggle to put on foliage. Years of infestation at a level that causes defoliation can eventually bring about death in forest trees.
Lucky for us and our forests, they do not exist in the destructive phase forever. Metamorphosis is an incredible occurrence and the caterpillars are nearing the process of changing into a moth. The moth stage will be focused solely on reproduction and our trees will get their much-needed respite. After mating, females lay a single egg mass containing between 200-1000 eggs. They are about the size of a quarter and are covered with a mat of fine hairs. These egg masses are usually laid in protected locations such as the underside of tree trucks/branches or overhangs on roof lines and house siding.
The obvious question is what can be done about the problem? On a landscape level, nothing can be done this year. Helicopter pesticide application is the preferred method to kill the spongy moth larvae. That must be done early in the caterpillar growing season (usually early May). The pesticide sits on leaves and is consumed by caterpillars and kills them from the inside. Spraying once the defoliation is actively occurring will not stem the tide. As a homeowner, keep stressed trees watered to aid the leaf out process. If you see egg masses on your home or trees, scraping them off and disposing of them is encouraged.
The Nature Foundation and WPOA will be prepared if the infestation of spongy moth continues to grow. Pheromone traps will be deployed to trap male moths this summer. If populations are deemed high enough, we will survey high population areas for egg masses which will determine where we will need to spray the following spring. If you are seeing defoliation, please email Josh Palumbo at forestmanage@tnfw.org.
