Swallowtails - Neighborhood Naturalist

Nature you can find in town and the nearby countryside
Corvallis, Oregon
Summer 2012
Swallowtails
article, photography and illustrations by Lisa Millbank
F
loating on a summer breeze or sipping nectar from
a flower, a swallowtail is the embodiment of the
carefree days of summer. But strangely enough,
before it became a colorful, winged adult, it resembled a
bird dropping, a big-eyed green monster and a piece of bark!
A swallowtail has an interesting life cycle that incorporates
chemical defenses, bizarre camouflage, an intimidating
disguise and delicate beauty.
Swallowtails differ from all other butterflies in their
wing venation, but a more peculiar feature is found on the
caterpillar. Only swallowtail caterpillars have a defensive
organ called an osmeterium, which secretes strong-smelling
chemicals. This fleshy, forked structure is usually concealed
A Western Tiger Swallowtail feeds on penstemon nectar
behind the head. If you gently touch or press on a
swallowtail caterpillar’s body, it will extend its osmeterium.
To the human nose, the defensive odor can be somewhat
pleasant, but it probably repels other creatures intent on
eating the caterpillar.
A Pale Swallowtail rests in the shade on a hot day
We have four representatives of the swallowtail family
in our area, and Western Tiger Swallowtails are by far the
most common of these. These large swallowtails, patterned
with sunny yellow and bold black stripes, flit along wooded
rivers and streams, where forests of Black Cottonwood,
Red Alder, Oregon Ash and willows ensure plenty of food
for caterpillars. But they’re also happy to feed on planted
poplars, ashes, plums, cherries, willows and sycamores in
yards and parks.
Neighborhood Naturalist, Summer 2012 v10 #2 • page 1
suitable caterpillar food plants like Queen Anne’s Lace
and Cow Parsnip are abundant in the valley, it’s a special
occasion to see an Anise Swallowtail in the lowlands.
The Anise Swallowtail has dark patches on the forewings.
Though they also have bright yellow markings, Anise
Swallowtails are smaller than Western Tigers, and have
extensive black areas on the forewings. The black patches
are visible even when the butterfly is in flight. Locally, Anise
Swallowtail caterpillars eat lomatiums, Cow Parsnip, Water
Parsley and other members of the carrot family. But female
Anise Swallowtails will also lay eggs on cultivated fennel and
dill in yards and farms. In the mountains, caterpillars eat
lomatiums, lovages and angelicas. Even though seemingly
Ne i g h b o r h o o d Na t u r a l i s t
promotes interest about nature
in mid-Willamette Valley
backyards, neighborhoods, and
countryside.
Visitors to the nearby foothills and mountains are likely
to see Pale Swallowtails in flower-dotted meadows and
hilltops. The black markings of the Pale Swallowtail are a
bit heavier, but otherwise nearly identical to those of the
Western Tiger. Between the black stripes is a white to cream
color. Although Pale Swallowtail caterpillars eat the leaves
of a wide variety of
common plants, such
as Oceanspray, Red
Alder, Serviceberry,
Cascara, plums and
cherries, we don’t often
see them in the valley
lowlands. The blackand-white stripes of
the Pale Swallowtail
sometimes cause
confusion with an An Anise Swallowtail caterpillar on
eastern species that
Barestem Lomatium
doesn’t occur in our
area, the Zebra Swallowtail.
There’s one final, surprising member of the swallowtail
family, and it looks nothing like the other three. The
Clodius Parnassian is much more likely to be found in
the Coast and Cascade Ranges, and only occasionally
in the valley. It has translucent wings marked with dark
bars. But like all members of the swallowtail family, its
caterpillar has an osmeterium, albeit a small one. Clodius
Parnassian caterpillars feed on Pacific Bleeding-Heart and
related plants.
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©2012 Don Boucher and Lisa Millbank.
A Clodius Parnassian feeding on Oxeye Daisy nectar
Neighborhood Naturalist, Summer 2012 v10 #2 • page 2
Western Tiger Swallowtail Life Cycle
about 1 mm
in diameter
egg
ald
ow
will
er
adult
caterpillar after
second molt
ash
cottonwood
caterpillar food
plants
silk girdle
eyespots
prominent
dark stripe
on chrysalis
osmeterium extended in
defensive posture
chrysalis
turns deep brown
before pupating
caterpillar after fourth molt
cremaster attached to silk pad
The goal of adult swallowtails is to find a mate. Like
most butterflies, they use pheromones to find mates, but
swallowtails also use certain behaviors to help them locate
one another. Male Western Tiger Swallowtails patrol along
riverside forests and watercourses, or fly along tree-lined
streets in cities, looking for females. Pale Swallowtail
males engage in a common butterfly breeding behavior
called hilltopping. The butterflies congregate on prominent
hilltops, which function like lepidopteran singles bars.
Male Clodius Parnassians stake out the caterpillar food
plant, Pacific Bleeding-Heart, in the hopes that a female
will show up. And male Anise Swallowtails hedge their bets
with a combination of patrolling, hilltopping and hanging
out near the caterpillar food plant.
Once she has mated, a female swallowtail uses her
antennae to detect the appropriate host plants for her
caterpillars. She locates them by sensing specific volatile
chemicals given off by the plants. She’ll lay eggs on the
foliage, one at a time. In warm weather, it only takes
about four days for the egg to hatch into a minuscule
caterpillar.
Neighborhood Naturalist, Summer 2012 v10 #2 • page 3
Like other butterflies, the Western Tiger Swallowtail
caterpillar spins a pad of silk and attaches its cremaster, a
cluster of small hooks on its abdomen, to the pad. Unique to
the swallowtails (except for the parnassians), the caterpillar
also makes a silken sling that it can use to suspend itself
head-up. It sheds its skin for the last time, and hardens into
a weatherproof shell with bark-like camouflage. Chrysalides
can be brownish to bright green depending on the season,
but generally have a prominent dark stripe down the side.
In the Willamette Valley, there are usually two or three
generations of Western Tiger Swallowtails every summer,
with the chrysalis stage lasting only a week or so in warm
A female Clodius Parnassian has just emerged from her cocoon (not weather. But the chrysalides formed later in the year will
a chrysalis, as is typical for butterflies). She will pump fluids from spend the winter in dormancy, until the warmth of next
May or June coaxes out the adult butterflies once again.
her swollen abdomen to extend her wings.
The Western Tiger Swallowtail caterpillar is the one most
likely to be found locally. Despite having an osmeterium,
this caterpillar also relies on two stages of visual deception
to protect itself, mainly from insectivorous birds. When
the egg hatches, the caterpillar resembles a tiny brownand-white bird dropping—something that birds obviously
avoid eating. For the first couple of molts, it continues
the unappetizing poop mimicry. Once it gets too big to
be a believable bird dropping, it molts into a vivid green
costume that blends in well with the leaves it’s eating. Two
large eyespots stare out from the top of its thorax. To a small
bird, it probably looks like an intimidating creature with a
startling gaze. It fattens up on a final eating binge after its
fourth molt. The caterpillar becomes quite pudgy, abruptly
stops eating, and turns from green to deep chocolate brown.
It’s ready to become a pupa, or chrysalis, and it wanders in
search of a suitable location.
Watch a video of swallowtails at
www.neighborhood-naturalist.com
A female Anise Swallowtail deposits eggs on fennel, a host plant.
A Western Tiger Swallowtail sips nectar from
Himalayan Blackberry blossoms.
In all stages of caterpillar development and pupation,
the Pale Swallowtail closely resembles the Western Tiger
Swallowtail. Anise Swallowtail caterpillars have a similar
bird-dropping mimic stage, but have well-developed spiny
protuberances on the back. After a few molts, they take
on a dramatically colored pattern of stripes and spots. The
nocturnal Clodius Parnassian caterpillars are black with
a row of spots along the sides, but their most interesting
feature is that they spin a moth-like cocoon around the
pupa, something highly unusual for a butterfly.
You can encourage adult swallowtails to visit your yard by
planting a wide variety of flowering plants (keeping in mind
that swallowtails are sensitive to insecticides). Swallowtails
are particularly fond of zinnias and penstemons. Female
Western Tiger and Pale Swallowtails will lay eggs on native
and introduced shrubs and trees of many kinds. Attract
Anise Swallowtails by planting fennel or dill—as long as
you don’t mind sharing your plants with some brilliantlycolored caterpillars! ó
Neighborhood Naturalist, Summer 2012 v10 #2 • page 4
American Goldfinch
article and illustrations
by Don Boucher
photography by Lisa Millbank
A
nybody who feeds wild birds knows about the
gregarious American Goldfinch. Have you ever
wondered why American Goldfinches are one of
the most reliable feeder species? The short answer is that
they’re seed specialists. But it’s a little more complicated
than that. American Goldfinches may be familiar, but they
have an uncommon life cycle.
Other species like chickadees, nuthatches, sparrows and
even other finches visit seed feeders in a typical seasonal
pattern. In fall, winter and early spring they visit regularly.
By mid-spring and summer, they visit less often, or are
absent altogether. These birds need a lot of high-protein
nutrition for breeding activities such as producing eggs
and raising fast-growing chicks. They meet this need by
hunting for insects or other animal foods, and lose interest
in your bird feeders.
of seeds to their babies, a diet unusual among songbird
nestlings. That’s why they’re still emptying your feeders in
mid-summer.
While visiting your backyard feeders, they may prefer
nyjer seed to sunflower seed. Nyjer seed (also called niger
or thistle seed) is a domestic crop bred from sunfleck, a
sunflower relative native to Africa. I suppose the tiny nyjer
seeds most resemble their preferred wild foods. Other birds
that eat a steady diet of juicy bugs or fruit in summer get
a substantial amount of moisture this way. The American
Goldfinch’s metabolism can conserve water well, even
on a diet of dry seeds. But I’ve noticed that American
Goldfinches are frequent visitors at watering holes and bird
baths in summer, maybe due to their low-moisture diet.
American Goldfinches occasionally eat bugs, but they’re
really geared to eat seeds, especially seeds from plants in
the sunflower and thistle family. That’s why gardeners plant
sunflowers, not only for the showy blossoms, but also to
attract these pretty finches. In the wild, they depend on
seeds from plants whose seeds ripen in mid-summer. That
includes seeds from both introduced and native plants such
as thistles, wild lettuces, tarweeds and others.
The American Goldfinch’s life cycle coincides with this
summer seed abundance. In our area, they nest in July and
August. That’s later than most birds, and even later than
their closest relative, the Lesser Goldfinch, which begin Tarweeds are native plants that provide food for goldfinches and
nesting in May. Adult American Goldfinches get plenty other seed-eaters. This American Goldfinch is eating tarweed seeds.
of nutrition from seeds, but they also feed large quantities The yellow blossoms pictured are Elegant Tarweed flowers.
Neighborhood Naturalist, Summer 2012 v10 #2 • page 5
This breeding male is pale
yellow, probably due to lack
of carotenoid pigments in
his diet during spring molt.
A goldfinch nest is a tidy structure
of small twigs expertly woven into
a tight basket. It is then lined with
fluffy plant down, often from thistles.
American Goldfinches are also our only finches that molt
twice a year—once in spring, and again in fall. The timing
of this molt varies among individuals. In fall and winter,
males and females look similar. Sometime in spring, the
males take on their lemon-yellow breeding plumage while
the females become a little more bright and crisp-looking.
A breeding pair in summer
A male on Canada Thistle
the mnemonic per-chick-o-ree to describe it. I once heard
about the mnemonic po-ta-to chip! and I found it so silly
but apt that it’s helped me recognize American Goldfinches
by sound ever since. Lesser Goldfinches and Pine Siskins
have their own distinct flight calls as well.
Watch a video of
American Goldfinches at
In our area, they’re year-round residents and remain in
www.neighborhood-naturalist.com
flocks all year except while nesting. Pair bonds are formed
in late winter. During courtship, females beg from males,
similar to the way fledglings beg from parents. Males sing
As sociable, flocking birds, American Goldfinches have
their extended twittering songs and perform circling display many other calls besides the po-ta-to chip! flight call, and
flights while singing.
you can become familiar with them. Try listening to them
for a while. Crack open the window by the feeders, or sit
By summer, breeding pairs leave flocks and establish in the yard or garden and calmly wait for them to get used
nesting sites. When you watch American Goldfinches to your presence.
dismantling the seed heads of thistles, they may be
doing more than eating seeds. They line their nests with
From late July through September, most of the bird
thistledown or fluffy material from other plants such as world is a little lazy and quiet. Singing has dwindled,
cattails. The male feeds the female on the nest while she is nesting is nearly over, and many fledglings are feeding on
brooding, and both parents feed the babies.
their own. American Goldfinches are the exception. They’re
a summer extension of springtime bird activity. ó
The song is unusual among songbirds. For most
songbirds, a song is a pattern or phrase lasting a few
seconds. A singing session lasts part of an hour or longer
and consists of one to several songs, repeated many times.
But an American Goldfinch’s song is long and complicated.
Instead of singing specific, repeated songs, they go on
and on, almost without stopping, for the entire session.
Throughout the session, the pattern constantly changes
with a steady stream of twitters and call notes. Many people
still call goldfinches “wild canaries” for this reason.
Our other two goldfinch species, the Lesser Goldfinch
and Pine Siskin, sing this way too, and sound similar. The
European Starling also has an on-and-on singing style, but
the quality of its voice is quite different than a goldfinch.
Fortunately, the American Goldfinch flight call is
something a beginner can depend on. Many field guides use
A flock gathers on Tansy Ragwort
Neighborhood Naturalist, Summer 2012 v10 #2 • page 6
a♪ po-t
♫
ip!
h
c
to
a♪ po-t
♫
ip!
h
c
to
The goldfinch flight pattern is distinctive. They flap their wings in bursts of 3 to 5 flaps (fewer are shown in the illustration)
and then tuck their wings momentarily to dart through the air. This cycle creates a bounding, wave-like flight path that even
shifts from side to side a little. Other finches do this to some degree, but in the American and Lesser Goldfinches and Pine
Siskins, this pattern is pronounced. American Goldfinches often make a po-ta-to chip! (or per-chick-o-ree) call while flapping.
This flight call (occasionally given while perched) can be distinguished from Lesser Goldfinch and Pine Siskin flight calls.
American Goldfinch
male
Lesser Goldfinch
female
• Yellow or brown back
• Breeding male’s black cap restricted to forehead
• Legs and feet are usually pinkish
• Males and females are similar in winter
• White under the tail
• Immature has buffy wing bars
• Yellow-orange bill in breeding plumage
male
female
• Greenish to dull olive-gray back
• Adult male’s black cap extends to the back of the head
• Legs and feet are dark or gray
• Plumage doesn’t change seasonally
• Yellow or gray under the tail
• Immature male has patchy black cap
• Male has prominent white spots on his wings and tail
American male, breeding
American male, breeding
Lesser male
Lesser male
American male, breeding
American male, non-breeding
Lesser male, immature
Lesser male
American female, non-breeding
American female, breeding
Lesser female
Pine Siskins are goldfinches too, but are easily
distinguished from our other two species. Aside from
their streaky feathers, their key features are yellow on
the wing and tail feathers, and an ascending buzzy call.
Few are present in the valley during summer, and their
numbers from year-to-year vary widely.
Neighborhood Naturalist, Summer 2012 v10 #2 • page 7
Lesser female
Dragonfly Afternoon
Saturday August 4, 3:00-4:30 PM
Join us on a hot summer day to watch dragonflies
and damselflies fighting, mating and hunting
over the ponds! We’ll identify as many as
we can, and just sit back and enjoy watching
this dramatic spectacle. It’s possible to see a dozen
species of dragonflies and damselflies at this site.
Please bring binoculars and wear sunscreen. We’ll provide cold
drinks for everyone.
Meet us at the Bruce Starker Arts Park in Corvallis (parking lot
near duck pond and amphitheater).
In this issue:
American
Goldfinch
Swallowtails
Neighborhood Naturalist
5008 Technology Loop #9
Corvallis, OR 97333
EVENTS
Naturalist Adventures
Third Sunday of the Month, 9am-Noon
July 15 Meet at Avery Park Rose Garden: 1210 SW Avery Dr., Corvallis
August 19 Meet at Avery Park Rose Garden: 1210 SW Avery Dr., Corvallis
Starting in September, we will no longer be meeting at the Avery Park Rose Garden.
September 16 Chip Ross Park: Meet at parking lot at end of NW Lester Ave., Corvallis
October 21 Bald Hill Farm & Mulkey Creek. Meet at Oak Creek Dr parking lot. Corvallis
Come learn or share your knowledge about nature in the Willamette Valley. We look at birds,
flowers, animal tracks and all kinds of other things. Our nature walks are slow-paced and casually
structured. Bring along a hat, rain gear and shoes that can get muddy. Please, no dogs. Activities
are geared toward adults but children may enjoy them too.
Rain or cold will not prevent us from going out and enjoying nature. Remember to dress for the rainy
and/or cold weather.
For other events or more information:
www.neighborhood-naturalist.com
Don Boucher, 541-753-7689, [email protected]
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