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Column by Susan Vernon: Island Marble Butterfly Part I - May 2010


May 01, 2000, was a glorious afternoon for a walk. It seemed like all the wildflowers were in bloom and I was pleased to find seashore lupine casting an especially warm purplish-blue glow on the bluff trail near Cattle Point. Savannah sparrows were singing in the grass. Along the way, I spotted a medium-sized white butterfly that I did not recognize. It had subtle black markings including a black pattern on the tips of its forewings and greenish-yellow mottling on its hindwings. The butterfly was feeding on field mustard. I made a sketch of the stranger in my notebook. That evening, I consulted a field guide and found images of the large marble butterfly, Euchloe ausonides, that resides in Washington State east of the Cascade Crest. I wondered if the butterfly I had seen might be Euchloe, too.


Some time later I learned that biologist John Fleckenstein of the Washington Department of Natural Resources had collected an unfamiliar white butterfly at the south end of San Juan Island in the spring of 1998 while doing a survey. The specimen was initially identified as Euchloe ausonides, "unnamed subspecies" for the San Juan Islands. It appeared to be the same butterfly subspecies that was present on southern Vancouver Island and Gabriola Island, in the Gulf Islands of British Columbia, from 1859 until 1908 when it was thought to have become extinct. In 2001, scientists formally described this newly rediscovered subspecies as Euchloe ausonides insulanus - the island marble butterfly.

News of the island marble's presence prompted more surveys for the butterfly in the San Juan Islands in 2002 - 2004. In 2005, the Washington Department of Fish and Wildlife and other agencies, organizations and individuals conducted surveys for the butterfly on several islands in the archipelago and on mainland counties in northern coastal Puget Sound and the Olympic Peninsula, as well as on Vancouver Island. They found island marbles, but in small numbers, at several new locations – all on San Juan and Lopez Islands.

What an intriguing situation – the rediscovery of an "extinct" butterfly. Where had it been for 90 years? How had it gotten to San Juan Island from Vancouver Island, or had it resided here all along perhaps being mistaken for the common cabbage white butterfly? I was eager to learn more about the little Pieridae—a member of the family of whites, marbles, and sulphur butterflies.

One of my more memorable early encounters with Euchloe was at American Camp. Standing on a ridge overlooking the prairie on a sun drenched day in late April of 2004, I watched nearly thirty creamy white island marbles fluttering with rapid wing beats low over the grass keying on patches of field chickweed growing among a riot of western buttercups, sheep sorrel, willow-herb, field mustard, newly budding hyacinth brodiaea, and stork's bill. The little white butterflies rained down upon the plain. The rich yellow blooms of the mustard plants seemed to beckon the marbles from times gone by.

I returned to the site for several days watching the high spirited butterflies "hill topping" along the ridge and fluttering across the prairie investigating blooming wildflowers and seeming to reject death camas and chocolate lilies as nectar sources When the breeze kicked up, the marbles settled down in a grassy swale to wait out the wind.

I watched island marbles all spring and found another habitat that was a good place for this butterfly, too. Along a backbeach strewn with sun bleached driftwood, the marbles nectared on pepper-grass, yarrow, sea rocket and fiddleneck. Male and female marbles patrolled the beach with straight, strong, fluttering flights occasionally coming together in energetic airborne displays that I hoped would produce a new generation of butterflies to carry on their kind. Finally, as spring leaned into summer, the number of adults quickly declined as the winged phase of their life cycle came to an end. By the summer solstice, the backbeach had lost the luster brought by the little white papillons.

In 2005, I joined the Washington Department of Wildlife's island marble survey team to document the presence of island marble butterflies throughout the archipelago. During the ensuing five field seasons, the surveys produced both encouraging news and heartbreaking disappointments. Each field season has its own unique character: good or bad butterfly weather; the satisfaction of discovering new populations of island marbles far afield from their core location; and, sometimes, the frustrating experience of realizing that a once favored marble site has been lost to development or perhaps adverse winter or spring weather conditions.

Now, in 2010, another island marble season has begun. After nearly a decade of observing this rare butterfly, my anticipation of the field season—from early April through mid-July—has not waned. This spring we've seen sunshine, showers, stiff breezes, and even a hailstorm. I wondered, early on, if the contrary weather would give mixed signals to the marbles preparing to emerge as adult butterflies from the tiny gray chrysalides where they had overwintered. I began searching for adults in the grasslands and remnants of prairie early in the month as field mustard, an important host plant for the cryptic butterflies, began to bloom. By the second week in April, spring azures, silvery blues, cabbage whites, Sara's orangetips, and satyr anglewings had all taken to the air, a good sign that the marbles' appearance was drawing near, as well.

Among the sites where I had found island marbles in the past was a southwest-facing slope on San Juan Island along the shore adjacent to Haro Strait. The headland is steep, rocky, and a tangle of grasses and early blooming plants including field mustard and chickweed. Nearly every day that week, I sojourned to the shore and sat, sometimes for hours, watching and waiting for that first marble to appear.

Cabbage white butterflies - close in appearance to island marbles - were already there: four of them. They flaunted their floppy white wings and fluttered about the slope and down into a swale in an erratic pattern that made them hard to keep track of. When the sun disappeared behind a cloud, the butterflies disappeared into the grass. Some days it rained; other days the wind produced a chill that even I wasn't about to abide for long. And so, I practiced patience.

April 16 was a fine spring day. My hopes for finding my first marble of the season were high. By the time I got to my favored site, the temperature had reached 60 degrees. It was calm and clear - perfect marble weather. I scanned the familiar rocky slope by the sea, got reacquainted with the cabbage whites, settled into the grass with my camera and binoculars, and waited.

How many times, I thought, can I check the same four cabbage white butterflies fluttering in and out of view along the slope and over the ridge? With a wingspan of less than two inches, they were a tiny image to keep track of so far away. But I kept checking – looking for any faint sign of the black and white patterned wing-tips of the marbles, the black bars on its forewings (rather than black dots on the cabbage whites), or the yellowish-green coloring the rare little butterfly displayed on the underside of its wings.

The watching and waiting was not a chore. Tiny silvery blue butterflies animated the air with their swift, darting, sometimes aggressive, aerobatics. An immature bald eagle flew low across the slope casting a dense shadow over the scene. Two crows strutted up and down the ridge; black oystercatchers screamed along the shoreline; gulls slept on the beach; and the first seashore lupine bloomed nearby. The sound of the waves gently nudging the shore seemed to counter-balance the oystercatchers' outburst. It was a glorious afternoon.

After about forty minutes of watching cabbage whites, I grew restless and began a walkabout to check the tall grass for perching butterflies. I found cabbage white #5 basking on a leaf blade, possibly newly emerged and drying its wings. Red-winged blackbirds blared their audacious calls from a nearby wetland as I continued searching.

Then the moment I had been waiting for: my first glimpse of an island marble – Class of 2010. It fluttered earnestly down the slope heading straight for a patch of field mustard. It perched on the bright yellow inflorescence of one plant, then another, and another, supping on the flowers' sweet nectar, so energizing to its new life. The little white butterfly shone brightly in the sun, its black wingtips and distinct black rectangular bar on its forewings clearly diagnostic of the subspecies. The time was 2:43 p.m.

I watched the marble flutter about the rocky slope for several minutes. It was clearly focused on finding food. After years of monitoring this rare butterfly here in the islands – the only place on earth, perhaps, where it exists – I allowed myself the pleasure of welcoming another generation of marbles to the world. But as quickly as the butterfly arrived, it disappeared into the grass as the sun receded into a darkening cloudbank that had insinuated itself into the scene while I was preoccupied with my discovery.

There would be time enough to see more island marble butterflies as the season progressed. Getting this first glimpse of my icon of San Juan Island wildlife was enough for one day, and so I headed home - smiling.

NEXT - PART II: The island marble is one of the treasures of our wildlife community. Its survival is an inspiring story for changing times. The marbles' lives here on San Juan and Lopez Islands are fraught with threats to its longevity, but there is good work being done to help insure that this steadfast butterfly remains in our midst. Next time, I will recount the marbles' fascinating four-stage life cycle that spans nearly a year. Also, I will explain how islanders might get involved in helping island marbles thrive, and thus become a part of this amazing animal's life story.

NOTE: The island marble butterfly is listed by the Washington State Department of Fish and Wildlife as a state candidate species for possible listing as endangered, threatened, or sensitive. The U.S. Fish and Wildlife Service list the island marble as a species of concern. It is illegal under Washington State law to collect the island marble butterfly, even for catch and release, without a state permit. For more information about the island marble butterfly contact Ann Potter, Washington Department of Fish and Wildlife at ann.potter@dfw.wa.gov.

About Susan Vernon

Susan Vernon is a former executive director of The Whale Museum, co-founder of the San Juan Nature Institute, and author of Rainshadow World – A Naturalist's Year in the San Juan Islands.

SAN JUAN NATURE NOTEBOOK / ISLAND MARBLE BUTTERFLY copyright 2010 by Susan Vernon. No part of this column (text or photograph) may be reproduced without the expressed written consent of Susan Vernon. All rights reserved.

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Last modified onTuesday, 19 April 2022 23:44

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