Attack of the Gypsy Moths

Late last summer, I hiked the Beehunter trail with friends.  It was weird and creepy.  When we stopped, it sounded like it was raining.  The trail was littered with bits of leaves – like the schnitzels of paper after children have been practicing with scissors.  Normally, when you look up into a tree, you can see distinctive leaf shapes and recognize which trees are maples or oaks.  Not on this day.  The leaf shapes had been altered.

What sounded like rain was frass – caterpillar poop – falling on the leaves.  And it was these very same caterpillars responsible for the misshapen leaves and leaf fragments on the ground.

Gypsy Moth Caterpillar

During subsequent hikes, I also noticed a high density of egg masses on the trees – far more than normal.  Normal.  Ha.  Before 1869 normal would be zero.

Brought here by Étienne Léopold Trouvelot from Europe to Massachusettes with the intent of breeding a more robust silk worm, the Gypsy moth caterpillar escaped the laboratory and became a part of the northeast landscape.  Over the years, it has managed to spread as far west as Wisconsin, north into Canada, and south to Virginia or North Carolina.

Gypsy Moths overwinter as egg masses.  In spring – late April and into May, the caterpillars emerge and begin eating.  By late June or early July, they will reach their final instar and pupate.  About two weeks after pupation, the adults emerge.

gypsy moth laying eggs bug of the day
Left: Female laying eggs by Jeff Tome. Right: Male by Jenn Orth

Females are flightless.  Males will find the females by “smelling” pheromones with their large, feathery antennae.  After mating, the female lays approximately 500 eggs.  Because the female is flightless, the egg masses are found on trunks along with empty cocoons.

Gypsy Moth caterpillars will dine on over 500 species of tree leaves, both deciduous and evergreen.  A serious infestation can defoliate a forest affecting the trees’ mortality.  The New York State Park system defines an infestation as serious enough to treat when there are 1,000 or more egg masses per acre.  Last fall, teams surveyed the trees in high use areas of the park and found an AVERAGE of 5,700 per acre with some areas having in excess of 14,000 masses per acre.  Concern in these high use areas is for visitor experience in the park.  Camping and hiking is unpleasant when frass falls into your food, or you slip on caterpillars as you walk.  Yes, they are that plentiful in some places!

Gypsy moth pupae and egg sacs
Egg masses and empty cocoons – by John B.

Of bigger concern to me is impact on the ecosystems, in particular the old growth areas of the park.  Survey teams in the these areas found densities of egg masses ranging from 1,990 to 16,430 per acre.  It would be such a shame to see the huge old hemlocks affected by these voracious caterpillars, which will devour hemlock needles in their later instars.

To combat the infestation, the park is spraying Gypchek – a virus that targets the gypsy moth species, but is reportedly harmless to humans, pets, and other species of wildlife.  One dose was applied last week.  Another will be applied sometime this week.

I haven’t been to the park yet this spring.  I’m a little nervous about it.  Guess I’ll know soon enough when I attend the Allegany Nature Pilgrimage!

I found these files on the internet:

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3 thoughts on “Attack of the Gypsy Moths

  1. Another disturbing account of the devastation that can be caused by invasive alien species, I hope your old growth hemlocks are ok and I hope the spraying works!

  2. I wonder when or if we will ever learn our lesson about importing plants and insects without giving any thought to the absense of natural controls when they are taken from their native environments. I still see black circles of sticky tar around tree trunks, put there to keep gypsy moth caterpillars from climbing the trees back when I was a kid.

  3. So interesting to see this happening on the other side of the country this year. I’m in Washington State and we had a huge bloom of tent caterpillars last summer. It was just like you describe, with the paths sometimes slippery from caterpillars and the sound like rain and the totally altered landscape. By late summer, after the caterpillars were gone, there was still a distinct difference to the way the canopy looked. I work in the same park every summer (for the last 8 years) and it was really striking how different it looked. I know some folks who’ve lived next to the park for 25 years and have never seen a big caterpillar infestation like that. The park didn’t do anything (no fungus or other control method), so I’m very curious to see how it looks this year. I won’t be in that park until July. I read though, that the following year after a bloom like that is aften extra lush…all that caterpillar fertilizer is apparently good for something.

    Thanks for sharing all your pictures. I got here just cruising for nature blogs and enjoyed browsing through.

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