Gypsy moth outbreak appears to be statewide

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Gypsy moth caterpillar
A gypsy moth caterpillar.
Photo credit: Howard Russell, MSU Diagnostic Services

We received samples of gypsy moth caterpillars from Hillsdale County and Ontonagon County this past week, which pretty much indicates that our current outbreak is statewide in scope. It’s strange that fifteen years ago when gypsy moths were ravaging trees across the state, I would guess that nearly everyone could recognize a gypsy moth caterpillar if they saw one. After a long lull of very low gypsy moth populations, its seems that many people have forgotten what they look like. Here are some key characters to look for when you think you might be dealing with this bug. First, the caterpillars are very hairy and older caterpillars have easily recognizable pairs of red and blue spots that run down the back of the caterpillar. Younger caterpillars do not have these spots, but they do have a couple of other characters that identify them as gypsy moths. Like other lymantriids (the family of moths that gypsy moths belong to), they have a single mid-dorsal, eversible gland on the sixth and seventh abdominal segments. They also have large setae bearing verrucae (big hairy knobs) on each side of the first thoracic segment that look like big hairy warts on each side of the head.

Close up of gypsy moth head
A close up photo of a gypsy moth
caterpillar showing the large hairy
bumps along the side of the head.
Photo by H. Russell, MSU Diagnostic Services

Top view of mid-dorsal eversible glands
The mid-dorsal eversible glands on the
6th and 7th abdominal segments of a
gypsy moth caterpillar shown slightly
from the side. Photo by H. Russell, MSU
DiagnosticServices

Sample of gypsy moth caterpillars
The sample of gypsy moth caterpillars
that came from Ontonagon County in the
western Upper Peninsula of
Michigan.

Mid-dorsal eversible glands
A top view of a gypsy moth caterpillar
showing the mid-dorsal eversible
glands on the 6th and 7th abdominal
segments. Photo by H. Russell, MSU Diagnostic
Services

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