Throughout much of New York State earlier this summer, fuzzy caterpillars were rampaging through natural forests and well-kept gardens alike. Maybe you noticed these bristly little critters wobbling along, or even had an itchy rash after touching their mildly stinging hairs!
These crazy caterpillars are Lymantria dispar, which you may have called gypsy moths in the past. Why not just call them gypsy moths? What is really in a name?
This is an exciting time as we wait to hear the new official common name for our moth, Lymantria dispar, but for this blog post we’ll call them L. dispar for short. Currently, the Entomological Society of America has is considering options for new names under the Better Common Names Project, in order to “bar names referencing ethnic or racial groups and names that might stoke fear.”
There is a plethora of fun characteristics for this moth which could apply to a new name. I personally vote for something akin to “Pricklecater,” “Blue-Red Spotted Messworm” or “Itchy Eww Moth.”
Anyways… back to our story.
A native of Europe, L. dispar were accidentally released into the wild in 1869 and have since become “naturalized” in 19 Northeastern states. This means they have shoved their way into local food webs as they munch down on foliage then in turn become a tasty food source for birds, bugs, and other predators.
For the most part, they are active participants in the wonderous world of ecology. They are citizens playing their part in a complex and everchanging ecosystem. A single L. dispar caterpillar can eat about a square meter of plant material during its short lifetime, but one caterpillar doesn’t do too much damage.
The problem is that one female moth can lay more than 1,000 eggs in a single mass, which stick to the sides of trees, and are browish and gummy-looking.
That’s a lot of eggs!
Every 10 to 12 years, the L. dispar population explodes exponentially and hundreds of thousands of tiny caterpillars hatch in the spring. Once hatched, they use a strand of silk to “balloon” away on the wind until they find a newly leafing tree to eat and eat and eat.
To experience these numbers, I’d like you to imagine walking your favorite path in the woods. Shaded from the hot sun, you can hear the gentle pitter-patter of rain sprinkling down through the canopy. How peaceful… There is no better place in all the world on this cloudless day.
“Cloudless day? But isn’t it raining?” you ask.
Oh yes, something is raining down… but it’s not water.
Scientifically known as frass, this tiny spherical poop from thousands of very hungry caterpillars is dropping down onto your head and shoulders, as these little machines diligently convert the lush green leaves overhead into little brown balls of poo.
Not great. Pretty gross.
These baby caterpillars have small, young jaws, and prefer soft new budding leaves until they are old enough to chew tougher vegetation. While the prefer hardwood trees, they will eat more than 300 different plant species when hungry enough, stripping away all foliage until trees and bushes are left embarrassingly naked
This can be a problem.
When deciduous trees like oak, birch and maple are eaten by caterpillars, they usually have enough stored energy to push out another set of leaves before the summer is through. It takes multiple years of defoliation to weaken these trees to the point of death. However evergreen trees cannot bounce back as quickly. Coniferous (evergreen) trees put lots of energy into their tough, thick, needle-like leaves, and will likely die if more than half of their needles are eaten.
Most years the caterpillars are fairly harmless, except during these incredibly destructive outbreaks which reoccur in a slow but disastrous cycle. Due to this pattern, L. dispar are considered cyclical pests.
In the adult stage L. dispar moths are not destructive at all, as they do not eat anything (no digestive system) and only live for a few days. The white fluffy females have pretty wings used for decoration rather than flying, and release a hormone into the air for male moths to find them. Females remain on the sides of trees as the males fly in search of the females’ scent.The female will lay fuzzy egg masses on whatever surface she’s near and the life cycle will begin again.
This is where we can take some control over the situation. By counting the egg masses in the wintertime, we can predict how many L. dispar caterpillars will hatch in the Spring and we can prepare a plan of defense.
Natural Population Controls
While major L. dispar outbreaks can resemble a plague of locusts consuming everything in their path, nature often has a way of correcting imbalances. At low densities, vertebrate predators keep the population in check, but are ineffective at controlling massive numbers of prey. Bird bellies just aren’t big enough!
However, when L. dispar caterpillars are densely packed into one area, viruses and funguses can spread rapidly. These are naturally occurring diseases which are always present in the environment, but only take significant effect when populations are grossly out of control. Researchers have identified one virus specialized to L. dispar which kills 90 percent of infected caterpillars. This virus has since been converted into an effective treatment which brings the population down to healthy levels.
This natural method of population control is the preferred way to control the situation since it doesn’t harm any other species. However, this treatment must occur very soon after the caterpillars hatch, otherwise the damage will already be done.
These last few months we’ve seen many caterpillars eating their way through New York, and next year could be even worse in some places… or not. It all depends how well nature’s natural defenses have worked.
Measures are being taken at State Parks to perform egg mass surveys to try and predict next year’s population and prepare for any treatments accordingly. Let’s not repeat the summer of 1981 when 13 million acres of forest were defoliated! Our poor defenseless trees!
Post by Juliet Linzmeier, Student Conservation Association member, Invasive Species Unit, NYS Parks
Cover shot – A L. dispar caterpillar. All shots from NYS Parks.
DISCLAIMER: The following materials have not been updated on the new common name for L. dispar, and refer to this pest as “Gypsy Moth”.
Want to learn more about these moths and efforts to protect the forest? The DEC has great information here at Gypsy Moth – NYS Dept. of Environmental Conservation
Prefer watching videos? The DEC also did a 30-minute Facebook Live post, which covers the history, morphology, control methods, and more!