Caterpillar Invasion Returns for Encore, Stripping Trees, Shrubbery,
in Our Hair
By IAN FEIN
They dangle down on silken threads and stick to your shirt or in
your hair. They crawl up the sides of homes and infest your trees. You
can hear them munching away on leaves, their frass falling to the ground
like rain.
Caterpillar tales are spreading around the Island like horror
stories, as the Vineyard - like other parts of southeastern
Massachusetts - undergoes one of the most memorable caterpillar
outbreaks in decades. More than a quarter million acres of trees were
defoliated statewide last year, and already this summer large swaths of
trees off Lambert's Cove Road in West Tisbury and near the blinker
in Oak Bluffs have been decimated.
SRC="http://www.mvgazette.com/news/2006/06/09/content/caterpillars_bare_branches_sm.jpg" The sticky topic arose in selectmen's meetings in three
different towns this week, with both Tisbury and West Tisbury boards
discussing the possibility of pursuing massive townwide spraying.
Anyone who has stepped outside on the Vineyard this week will attest
to the inconvenience and discomfort posed by the army of caterpillars,
but many arborists and entomologists are concerned about widespread
overreaction to what is almost certainly a temporary natural cycle.
"People certainly have a natural aversion to the
overpopulations, but this type of thing has repeated itself
before," said Tim Boland, executive director of the Polly Hill
Arboretum, which hosted two caterpillar forums this winter and spring.
"I would urge people to be conservative in their approach and not
be too aggressive in spraying. If we were to globally spray everything,
we would lose a good portion of our native biodiversity."
Although caterpillar outbreaks are a relatively common cyclical
occurrence, the current situation is somewhat unique in that it involves
several different species sustained over multiple seasons.
Massachusetts Natural Heritage and Endangered Species Program
restoration ecologist Tim Simmons said yesterday that significant
declines in the caterpillar populations may not be seen for another
decade.
"We're going to see massive defoliations for at least
another ten years at least. It should take that long for natural or
introduced parasites to catch up," Mr. Simmons said.
"It's going to be a while."
There are five different types of caterpillars feasting on Vineyard
trees, including three native species: the eastern tent caterpillar, the
fall cankerworm and the forest tent caterpillar, which has not seen such
outbreak numbers for more than 100 years.
Two non-native species - the gypsy moth and winter moth
caterpillars - are also present on the Island. While the gypsy
moth has been around for more than a century and reached outbreak
proportions statewide in the 1980s, the European winter moth was first
seen in the region only a few years ago. Some state entomologists
studying the current outbreak have theorized that the introduction of
the winter moth may have distracted some of the predators of native
caterpillars, leading to an overabundance of multiple species.
SRC="http://www.mvgazette.com/news/2006/06/09/content/caterpillars_steve_masterson_sm.jpg" Most of the caterpillar types typically appear in very large numbers
for a few years before subsiding rather dramatically. They usually
defeat themselves by overfeeding, or a change in ecological conditions
might cause a rise in a particular fungus or parasite that controls the
caterpillar population.
The winter moth situation is slightly more concerning to
entomologists because there are no known predators here at this time. A
nonnative predatory fly species has been identified and is now being
studied for possible release, but some biologists have warned against
it. Another parasitic fly that was released on the Vineyard to control
the gypsy moth population in the 1980s is now partially blamed for the
decline of the threatened imperial moth.
Over time, the caterpillar feasting could eventually have an impact
on the Vineyard tree population. Many of the younger trees will likely
re-leaf later in the summer, and although a season without leaves does
not pose an immediate threat to a tree, those that are defoliated year
after year can die within a few years.
Island biologists have noted that many of the caterpillar
populations appear to be rotating around the Vineyard over the last few
summers, which might prevent some repeated defoliation. Also, some tree
deaths might not be a bad thing for the Vineyard environment; it could
open the canopy for smaller native plant species that have been blocked
out by oaks.
At least four different tree service companies have been busy
spraying on the Island over the last few weeks. While most have been
using an organic substance called Conserve SC, there is not unanimity on
the potential impacts that the compound might have on other plant and
animal species. And at least one company has been using a moderately
toxic pesticide.
Sheriff's Meadow Foundation - a conservation
organization and the largest private landowner on Martha's
Vineyard - decided not to spray any trees on its more than 2,000
acres this year, because the solutions currently available are not
species specific and might harm native moths and butterflies.
SRC="http://www.mvgazette.com/news/2006/06/09/content/caterpillars_eaten_tree_sm.jpg" Mr. Boland said it is probably too late for spraying to have much of
an effect on the caterpillars at this point anyway, and he recommended
that homeowners should regularly water the defoliated trees they want to
protect over the long term. At Polly Hill they sprayed Conserve SC on
some of their oldest trees that they consider irreplaceable, but Mr.
Boland specifically warned homeowners against spraying anywhere near
native pitch pines or frost bottoms, which some rare moths are known to
inhabit.
Although the caterpillar species are on somewhat different
schedules, many are expected to migrate into the soil within in the next
week to spin a cocoon and pupate, only to reemerge as moths later on.
Mr. Boland suggested that people try to take the long view when
thinking about the caterpillars.
"Nature does have the ability to rebound, and that's the
thing to remember," he said. "Things will eventually even
out."
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