The Outside Story
yellow with thin black stripes. I consulted
my butterfly guides and determined the
fabulous creature was a giant swallowtail,
a cousin to our common Canadian tiger
swallowtail.
Until recently, giant swallowtails, North
America’s largest butterflies, were only
occasional visitors to southern New
England, and absent from our region. But
since 2010, these big butterflies have
been seen in increasing numbers in the
Northeast.
Giant Butterflies Moving
North
By: Susan Shea
It’s a bird, it’s a plane, it’s a …? In
September of 2012, I spied something
fluttering wildly on the lavender phlox in
front of my house. At first I thought it was
a hummingbird, but as I moved closer I
discovered it was a huge butterfly – the
largest I’d ever seen, with a wingspan of
about six inches. I rushed into the house
to get my camera.
The butterfly was a challenge to
photograph, its wings a blur as it hovered
and darted from flower to flower, sipping
nectar with its long tongue. The upper
side of its wings were black, with a band
of yellow spots from wingtip to wingtip.
Another yellow band led diagonally from
each wingtip to each wing “tail.” The tails
were long, with yellow spots edged in
black. On the underside, the coloration
was similar to a tiger swallowtail – pale
According to Kent McFarland, a
conservation biologist with the Vermont
Center for Ecostudies, the giant
swallowtail is known to wander, and feeds
on a wide variety of flowers. He theorized,
“they probably had good productivity in
the South and their population was able
to explode and move north in the warmer
weather of recent years.” McFarland
noted that this sudden range expansion is
not unprecedented. “There are accounts
of giant swallowtails in the Northeast
from the late 1800s. Samuel Hubbard
Scudder, a famous lepidopterist, had
records of giant swallowtails up into
Quebec. There were big flights into the
Northeast that lasted for several years,
then disappeared, perhaps due to colder
weather.”
Giant swallowtail caterpillars have been
found in Vermont on prickly-ash, a shrub
in the citrus family. This is the only known
host plant native to our region, and the
caterpillars' presence is evidence these
butterflies have reproduced in the
Northeast. People have also found them
on potted citrus trees on their porches,
said McFarland. (In Florida, where giant
swallowtails
are
abundant,
these
caterpillars are a pest in citrus groves and
are known as “orange dogs.”)
When the caterpillars first hatch from tiny
orange eggs, they look like bird droppings,
a disguise to foil predators. As they
munch on leaves, they grow to two inches
long, and become brown or olive with
white patches and small purple spots. At
this time they resemble small snakes, with
a swollen thorax that mimics a snake
head. When attacked, they project a red,
Y-shaped gland that looks like a snake’s
forked tongue. The gland contains a
pungent mix of chemicals that are toxic to
small predators like spiders and ants.
Keep your eyes open for the spectacular
giant swallowtail this spring and summer.
You
can
report
sightings
on
http://www.e-butterfly.org
Susan Shea is a naturalist, conservationist,
and freelance writer who lives in
Brookfield, Vermont. The illustration for
this column was drawn by Adelaide Tyrol.
The Outside Story is assigned and edited
by Northern Woodlands magazine and
sponsored by the Wellborn Ecology Fund
of New Hampshire Charitable Foundation:
[email protected]
The caterpillar’s skin eventually hardens
into a brownish case or chrysalis, where it
spends the winter. Inside the chrysalis,
attached to a branch or fencepost with a
silken thread, the caterpillar transforms
into a butterfly. In spring, the butterfly
splits the chrysalis open and emerges.
Holding onto the shell of the chrysalis, it
pumps fluid into the veins of its wings
until they are fully extended. Once the
wings are hardened, the giant swallowtail
takes its first flight. These butterflies have
a distinctive flight pattern – they appear
to be “hopping” through the air, and they
tend to fly high and fast. They produce
two broods annually in the North.
Fresh giant swallowtails have been seen in
southern Vermont and the Champlain
Valley in May in recent years, evidence
that they have overwintered successfully
here.
Did giant swallowtail chrysalises survive
this year’s cold winter, or will the species
retreat south again? “We’ll have people
looking,” said McFarland. “It will be
fascinating to find out.”
PO Box 471, Corinth, Vermont 05039
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This article is reprinted with the permission of the Center For Northern Woodlands Education. A not for profit
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understanding of and appreciation for the natural wonders, economic productivity and ecological integrity of the
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