News Feature

Blue Hill
Originally published in The Weekly Packet, June 7, 2018
Forest tent caterpillars cause havoc on Mines Road

Slippery when wet

Motorists reported a stretch of the Mines Road as slippery as driving on “black ice,” prompting town officials to engage the Department of Transportation, which placed signs on either end, said Selectman Jim Schatz.

Photo by Faith DeAmbrose Order prints of selected PBP photos.

by Faith DeAmbrose

Along a two-mile stretch of the Mines Road in Blue Hill an outbreak of the native caterpillar known as the forest tent caterpillar is making itself known. The pests have deforested acres of hardwood trees, have covered homes and traveled across the roadway, causing a mess so slippery that the Department of Transportation has set up electric signs warning motorists. There is also a lingering odor in the air.

The forest tent caterpillar is attracted primarily to oak trees, but will also feed on other hardwood trees such as poplar, aspen and sugar maple.

The caterpillar is native to Maine, and it is usually kept in check by environmental factors and pests. Those natural controls, explained Forest Entomologist Allison Kanoti of the Maine Forest Service, such as parasites and disease, were not sufficient enough this year to preempt an outbreak.

Last year, said Kanoti, approximately 70 acres of trees were deforested by the forest tent caterpillar in much the same Mines Road location. She said that, this year, the caterpillar seems to be stripping the trees more quickly and may have started to feed earlier. “In most years people won’t notice” when the caterpillars feed, she continued, but said that an outbreak can last anywhere from three to five years until nature returns to balance.

And, while the Mines Road area has garnered much attention by passing motorists, parts of Brooksville and Brooklin have also historically experienced defoliation by the caterpillar.

What about the trees?

Leaves enable photosynthesis, thereby producing the energy for a tree, said George Fields of Blue Hill Heritage Trust. The absence of leaves is problematic, but that factor alone, over a year or two’s time, will not kill a tree. However, explained Kanoti, when other factors are present, such as drought or when trees grow in poor soil, the effects could be more severe. The Mines Road area, she said “is a challenging site because the soil is not deep and trees can dry out quickly if there is a drought.”

Once caterpillars start to move, treatment with pesticides will not make much difference, said Kanoti. The time to treat trees is early May, and the preferred pesticide is called Bt (bacillus thuringiensis), which specifically targets caterpillars.

As the cycle continues, in the fall, forest tent caterpillar eggs will be deposited at the tips of a host’s tree branch in a tightly woven web. The eggs will overwinter and caterpillars will emerge in late May.

Despite their name, the forest tent caterpillars do not create a proper tent, and instead live in a silk webbing until hatched. They feed for approximately six weeks and are expected to continue destruction throughout June.