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Spongy Moth

Spongy moth, (Lymantria dispar dispar, LDD; formerly gypsy moth) caterpillars were responsible for the largest disturbance to Vermont forests as mapped through aerial detection surveys in 2021. Defoliation was significant in the Champlain Valley of western Vermont, with 50,945 acres mapped as moderately or severely defoliated.

Spongy moth caterpillar
Spongy moth caterpillar
Spongy moth egg masses
Spongy moth egg masses


2021 Defoliation

One year of defoliation is unlikely to cause substantial damage to most hardwood trees, but repeated defoliation can have significant impacts on tree and forest health. The fungus Entomophaga maimaiga helps control populations of spongy moth when spring conditions are wet and/or humid. The drought from 2020-2021 may have allowed spongy moth populations to build and expand, and likely contributed to the current outbreak. Outbreaks collapse from a combination of factors: starvation, malnutrition, viral or fungal diseases, and high rates of parasitism.

Spongy Moth Distrubtion
Spongy moth defoliation 2021. Mapped area includes 50,945 acres affected.


Spongy moth landscape
2021 landscape defoliation.



Egg Mass Counts

Spongy Moth Counts
Egg mass counts from nine focal area plots in 2021 increased from 2020 levels and suggest that defoliation is likely to be observed again in Vermont in 2022.


More information about spongy moths: