GOOD, BAD, UGLY: Actually, when it comes to caterpillars they do
fall into those three categories – although none of them are what
we’d call “cute.”

Andrew Sidelinger, forester, Elk State Forest, helps us sort out
the ones we see most often in or near the woods. The cast of
characters includes the forest tent caterpillar, eastern tent
caterpillar and the gypsy moth caterpillar which are often found in
the same area or even on the same trees.

The two tent caterpillars are native to Pennsylvania while the
gypsy moth is an introduced or non-native species.

“Trying to predict insect populations is like trying to predict
the weather,” Andrew writes. Based on last year’s observations,
forestry officials hoped the numbers would drop or at least stay
the same but, instead, they exploded.

“The majority of the caterpillars causing damage in the forest
were forest tent caterpillars, leaving large areas of
defoliation.”

The eastern tent caterpillar has a continuous white stripe along
the length of its body, the forest tent caterpillar has keyhole or
footprint-shaped white spots along its back; and gypsy moth
caterpillars have a double row of hairy dots along their back with
four sets of the dots being blue and the rest being red in
color.

Eastern tent caterpillars feed primarily on black cherry trees
along with other trees in that same family such as apple, crab
apple, hawthorn and pin cherry. Forest tent caterpillars prefer to
feed on sugar maple, oaks and basswood. If populations are large
enough, they will feel on other species as well.

Gypsy moth caterpillars prefer the oaks; however, when
populations are large enough, they will also eat other tree
species.

Healthy trees that are defoliated should leaf out again by
mid-summer, and generally a tree will recover from the first
defoliation. If trees suffer successive defoliations or a
combination of defoliation and other stressors, such as drought,
frost or anthracnose, this can increase the chance of tree
mortality.

Eastern tent and forest tent caterpillars are generally not a
long-term concern as they tend to move through an area and on to
another the following year, or the population will collapse due to
natural mortality. DCNR has been monitoring these outbreaks for
many years, and has never had to institute a statewide spray
program of either eastern tent or forest tent caterpillar.