Forest tent caterpillars: 2003 update
On the scene, but declining in 2003
Forest tent caterpillars (FTC) ate their way across over seven million acres of rural and urban forests in 2001 and again in 2002. In 2003, caterpillars are expected to be abundant in an area from Deer River through Grand Rapids and up through the Iron Range over to Virginia. Areas around Finland, Floodwood and Gooseberry Falls State Park also will have large FTC populations. However, the forest tent caterpillar population is on the downswing, so many areas defoliated in 2002 will have little or no defoliation in 2003, and most of the defoliation will be patchy
The "friendly fly" (a parasite that is a natural control of FTC)population is predicted to be high in 2003, especially in areas that had large FTC populations in 2002. For some, this fly will be more of a nuisance than the caterpillar. Friendly flies do not bite and are native to Minnesota.
Because the FTC, Malacosoma disstria, is a native defoliator of hardwoods, the impact of their defoliation on forest health will likely be minimal. But the impact on outdoor activities is noticeable. Abundant caterpillars, stripped trees, and bug poop dropping into your backyard BBQ can create an unpleasant environment. There are things you can do to minimize the inconvenience. See the list of suggested publications below.
Forest tent caterpillars prefer aspen and birch trees in the northern counties of Minnesota and basswood and oaks in central and southern counties. The caterpillars are often mistakenly called "armyworms" because of their habit of wandering around in search of food during population outbreaks.
Widespread outbreaks of FTC occur at intervals of 10 to 20 years and are two to three years in duration. Outbreaks peaked in 1922, 1937, 1952, 1967, 1978, and 1990. Populations collapse due to starvation, predation, and parasitism. Populations of the friendly fly, a native parasite of FTC, build up as the FTC populations peak and can themselves become a nuisance.
Forest tent caterpillar defoliation in 2002. [Legend: yellow = trace defoliation (1-25%); peach = light defoliation (26-50%); red = moderate defoliation (51-75%); maroon = heavy defoliation (75-100%)] |
In the forest, FTC defoliation usually does not affect tree health because FTC populations usually collapse before tree damage occurs. FTC can consume 60 percent of a tree's foliage for three years and the tree will show no ill effect. Even completely defoliated trees will develop a second set of leaves in early July without a loss in health. |
Projected schedule* for FTC life stages and host tree foliage |
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Host tree buds break |
April 18 - May 10 |
FTC hatch |
April 18 - May 15 |
FTC major feeding period |
June 5 - June 25 |
Host trees refoliate |
Early to mid-July |
FTC moths fly and lay eggs |
July 1 - July 15 |
*The timing of biological events varies from year to year because timing depends on weather and location. For example, events will occur near the earlier date when the spring is early, when May and June are hotter than average, or when the location is south of Mille Lacs. |
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Friendly Flies: A Fly that Parasitizes Forest Tent Caterpillars
More information on FTC and color photos can be found on these web sites:
