[ THE OUTSIDE STORY ]
Woolly Bears: Forecast Flops?
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hibernate. They may wander surprisingly far in their quest. Choice spots are
under leaf litter, in a wood pile, even behind loose bark. Here they are out of
the elements, but by no means protected from freezing. In fact, they must
freeze in order to survive the winter.
Like frogs, woolly bears make a substance that acts like antifreeze. As the
late autumn temperature drops, the caterpillar gradually fills with glycerol.
This viscous substance basically prevents organs and sensitive tissues from
getting freezer burn. The setae also contribute to the winterizing process
by drawing water out of the caterpillar’s body. Deadly ice crystals form
harmlessly on the bristles instead of inside the body, where cells critical to
life reside. Eventually, only the interior of each cell remains unfrozen, safely
surrounded by cold-tolerant glycerol.
With ice on the outside and glycerol on the inside, the caterpillar is ready to
endure a long period of cold weather. This period of arctic diapause is so critical
that a mild winter can spell doom for woolly bears. (So, too, can soft-hearted
but misinformed “protectors” who relocate one to the garage, “so the poor
caterpillar won’t freeze to death.”) Protected from snow and wind by its leaf or
log shelter, the frozen caterpillar can withstand temperatures well below zero.
Looking like a crispy tortellini, it lies as though lifeless until spring temperatures warm it up. Once it thaws, it resumes ravenous eating as though never
interrupted. After a few days of gorging on tender greens, the banded larva
finds a site to spin a cocoon. Woodpiles are again favorite spots, but any secure
surface will do. Every year I find four or five inside an empty wren house.
A miraculous transformation takes place over the next one to two weeks.
Then one day a delicate yellow-orange Isabella tiger moth (Pyrrharctia
isabella) emerges without warning. You’re not likely to see it unless you have
a porch light, however, as it is both nocturnal and short lived. It will mate, lay
eggs, and die in a matter of weeks, leaving its offspring to carry on the role
of pretend prognosticators.
Autumn is coming to a close. The brilliant fall foliage is
past peak, if not already layered in the compost bin.
The last geese are honking their way toward winter
homes. Predictions are proffered (sometimes cheerfully,
mostly not) for how cold and snowy this year’s winter will be.
Sources for seasonal predictions vary. The Farmers’
Almanac and traditional old wives’ tales are often cited. How
soon those geese head south, for example, is supposed to indicate how
difficult winter will be. We trust these bits of folklore because they seem to
work. (Research is advised, however; never assume that country wisdom is
reliable enough to calculate, say, your oil pre-buy needs.)
Sometimes the cuteness factor plays a role in our willingness to believe.
Take the woolly bear caterpillar, whose fuzziness often tempts people to pick
it up and, coincidentally, to discover that the bristles, called setae, are actually stiff and hard, not soft and cuddly. It is on the prowl in late fall, crossing
lawns, logs, and roads. According to tradition, the wider the rusty-orange
band around its middle, the milder the coming winter. The relative size of its
two black sections is also supposed to have meteorological significance. If
the front one is larger than the back, the beginning of winter will supposedly
have colder temperatures than the end of winter, and vice versa.
In fact, woolly bears are better predictors of the past spring and summer
than the coming winter. Like all caterpillars, the woolly bear goes through
several stages of development, called instars. Each instar is a period of
steady eating and growth, culminating in the shedding of now too-tight skin.
During each molt, some of the black-bristled segments are replaced with
orange ones. Fall is well under way by the fifth or sixth instar, just when we
begin comparing the forecast and the caterpillar.
What this means is that the ratio of black to orange actually depends on the
caterpillar’s age and developmental stage. Very young woolly bears are almost
entirely dark. If spring came early, the woolly bear will have had additional
time for growth, resulting in a wide orange band by fall. On the other hand,
lack of rain in the spring and summer may limit its food supply (dandelions,
grass, clover, nettles, and birches are preferred) and delay growth. Looking at
a stressed, spring-size caterpillar in November may tell you something about
the previous months’ weather conditions, but it won’t be much help with the
question of whether your wood pile needs supplementing.
As autumn edges closer to winter, these caterpillars seek out a place to
what species and product they are carrying. The
exercise serves as an informal barometer for
how much work is taking place in the woods. But
thanks to this study, we’re now able to assign a
dollar value to this wood as it relates to wages. If
we assume that there are about 3. 28 million tons
of wood harvested each year in New Hampshire
(that number is from timber tax data collected in
2012), we can calculate that every ton of wood
generates $32 in wages. To put this into perspec-
tive, if you pass an 18-wheeler on the highway,
the wood it’s carrying has created around $1,000
in local wages.
Of course, timber harvesting is just the tip of
the iceberg in New Hampshire’s wood economy.
Sawmills, biomass and firewood producers, wood
pellet manufacturers, and pulp and paper producers
all make huge contributions, too. We’ll tackle the
economics involving these businesses in future
Eric Johnson is the program director emeritus for the
New Hampshire Timberland Owners Association. He is
a former professional logger and maple syrup producer
from Andover, New Hampshire.