By Carol Stocker, Globe Staff | March 31, 2005
Region will be blanketed by caterpillars
The biggest caterpillar outbreak since the heyday of the gypsy
moth is expected this spring along the Massachusetts coast,
South Shore, the Cape and some areas inland.
1981 there were so many gypsy moth caterpillars, they stopped
trains that couldn't get traction on hills because they were
slippery and covered the tracks. They caused car accidents,
too. It was the Year of the Gypsy Moth. And this year is going
to be close to it!" Charles Burnham of the state Department of
Conservation and Recreation told a sold-out Brockton conference
of green industry professionals March 23.
But the problem isn't gypsy moths this time. Eastern tent
caterpillars, fall cankerworms, and forest tent caterpillars
are all out of control in some areas. ''A lot of caterpillars
are going wild. I'm seeing ones I never saw before," said
Robert Childs, extension entomologist at the University of
Massachusetts at Amherst.
The main culprit is a European insect never before seen on the
East Coast. It's called the winter moth because the adult moths
emerge from their cocoons in late November and December. If you
had a snowstorm of these tiny moths at your porch lights last
Christmas, your trees are in for trouble soon, thanks to their
voracious offspring. These will hatch as caterpillars in about
Originally reported on the South Shore and Cape Cod, the new
insect outbreak was thought to be an infestation of native fall
cankerworms, which were also in the area. These usually crash
from natural causes after about three years, so specialists
didn't think there was a problem.
But the South Shore defoliation has continued and spread for at
least a decade now. Horticulturalist Deborah C. Swanson of the
Plymouth County Cooperative Extension/UMass Extension, raised
the alarm (and kept raising it) and in 2003, and scientists at
the University of Connecticut and Cornell finally identified
the pest as a new arrival from Europe, Operophtera brumata.
''This was a tricky little critter that snuck in under radar
because it shares many of the same hosts as the cankerworm
caterpillar and looks very similar to it," said Childs. ''We
didn't notice it until Deborah started notifying us seven or
eight years ago and the first sample she sent were fall
cankerworms. There were a couple of winter moth caterpillars in
the second sample, but I thought maybe they were just spring
cankerworms. I asked for a third sample in 2003, and we sent
that to Dave Wagner in Connecticut," who first identified it as
Meanwhile, the new moth multiplied because it has no natural
enemies here. And even though the females are flightless, it
managed to spread. ''We know it's in the coastal towns from
Gloucester to Boston, in and around Boston out as far as
Newton-Wellesley, and pretty much throughout southeastern
Massachusetts, and most of the Cape out as far as Eastham.
There's going to be more research this year to locate it," said
Now the numbers at the center of the outbreak are astounding.
''We've got some crazy, incredible densities," said the Brenda
Whited of the UMass-Amherst survey team. Individual banded
maples and oaks in already hard-hit Hanson and West Bridgewater
last winter yielded up to 1,600 females laying eggs on each
tree monitored. Since winter moths can lay 150 eggs, that adds
up to almost a quarter of a million caterpillars this spring
per tree. Many of these inchworms may starve to death,
especially if they hatch before the tree buds swell, and
numbers won't be that large inside Route 128, as the moths just
reached here about three years ago. ''But it's going to get
worse for the next five years, at least," said Joseph Elkinton,
forest entomologist and ecologist at UMass-Amherst.
Then, if all goes according to plan, a counter measure will
start kicking in. Elkinton collected a predator of the winter
moth called Cyzenis albicans, in Nova Scotia, where they were
released to control a winter moth outbreak there 50 years ago.
He is now raising these caterpillar-killing flies in the
quarantine facility at the USDA lab Otis Air National Guard
Base in Falmouth. ''This is important because we need to make
sure that only Cyzenis is released and not some other organism
brought in accidentally with Cyzenis, which is very specific to
winter moths," Elkinton added.
But the moths have a big head start. ''It took five years for
them to multiply enough to catch up with the winter moth
population when they were released in Nova Scotia," Elkinton
said. After that the winter moth population declined
dramatically there over a couple of years, and has been kept at
a low level ever since.
Until then, however, you're on your own, and trees that have
been defoliated for several years are very unhappy. They face
decline and even death without extra help. (Canadian research
found that many trees die after four consecutive years of
complete defoliation, though this will vary with the tree
condition and species.)
The tiny green inchworms start with oaks, maples, fruit trees,
ash, rose-of-sharon and blueberry bushes, but almost any leaves
or flowers are fair game after that. One way to tell if you're
going to be hit hard is to check your tree trunks for the tiny
orange eggs the moths randomly scatter in bark crevices. Just
before they hatch, the eggs turn bright red.
The inchworms usually hatch around April 20 and immediately
weasel their way inside swelling leaf buds, where they cannot
be reached by sprays. The leaves open in tatters. After that,
the caterpillars are ''free feeders"; they spread by swinging
tree to tree like Tarzans on their own silken ropes when
looking for a new food source.
In the past, the state took the ''atom bomb" approach to
caterpillar outbreaks with massive and largely ineffective
spraying of chemicals such as lead arsenate and DDT. Now state
specialists have learned that introducing diseases and
predatory insects that kill only that pest is much safer, and
works better, too. A fungus from Japan called Entomophaga
maimaiga has all but finished the gypsy moth as a serious pest
since 1989, though it can recur when springs are dry enough to
inhibit the fungus, which needs wet conditions to thrive.
There are outbreaks of other caterpillar species as well, for
even the natives are restless. For some unknown reason, when
one type of caterpillar overpopulates, several other kinds
often follow suit. Perhaps the weather conditions suit them
all. Or the birds and other predators have been just too busy
keeping up with winter moths to get to them. Or perhaps when
there were more gypsy moths around, they spread their diseases
and pests to the other caterpillars, Childs speculated.
Winter moth caterpillars are active for only about three or
four weeks. Around May 20, they will dangle down to the ground
on skeins of silk and burrow into the top layer of soil, where
they will become dormant pupae until emerging as adult moths
between Thanksgiving and New Year's for their nighttime mating
ritual. They don't eat anything then. The males just flutter
around and mate with the flightless females, who clamber up
trees, lay eggs, and die. Then next April those eggs will hatch
. . . and on and on it goes.