Saturday, April 9, 2016

Marble-ous!

I am not one to get very excited about butterflies. They endear themselves to human sentimentality with little need for my literary intervention, thank you very much. Still, I am occasionally prone to bouts of surprise and effusive language when confronted by species I have not seen before. Such was the case last Monday, April 4, when my wife and I encountered a Large Marble, Euchloe ausonides, while hiking in Aiken Canyon Preserve, a The Nature Conservancy (TNC) property in El Paso County, Colorado south of Colorado Springs.

The common name of this butterfly is rather unhelpful, as it is not particularly "large." It has maybe a 5 centimeter wingspan at best, comparable to other average members of the family Pieridae, which includes the whites, sulphurs, and orangetips. The "marble" part of the name does effectively describe the reticulated pattern on the underside of the hind wing.

You would think that such a contrasting pattern would make the perched insect stand out, but it is the exact opposite. The butterfly has an uncanny ability to choose backgrounds that render it nearly invisible. Plus, it folds itself such that it can almost completely conceal the bright white forewing. Heidi and I watched this butterfly land, and in glancing at my camera to turn it on I lost track of it completely when I returned my gaze to where I knew it had alighted. The insect was able to orient itself in such a fashion that from my vantage point it was perfectly camouflaged. Even with Heidi's help it took me a good two or three minutes before the butterfly again resolved itself.

The Large Marble is a widely distributed species from Alaska to central California and extreme northern Arizona and New Mexico. There is but one generation annually at higher elevations, two at lower elevations. The adult insect is on the wing in spring in lower areas, in summer in mountain meadows.

At least one subspecies, the Island Marble, E. ausonides insulanis, is considered to be highly endangered, though it has not yet qualified for federal listing as such. It is now found only on San Juan and Lopez islands off the coast of northwest Washington state, according to the Xerces Society web page profiling this butterfly.

The caterpillar stage of the Large Marble is equally inconspicuous, being very slender, and vertically striped in yellow and blue-gray (with black speckles throughout) so as to blend perfectly with the delicate stems of the mustard plants it feeds on. Rockcress, Dyer's Woad, and Tower Mustard are among favored host plants in prairie and dry meadow habitats.

Spring White, Pontia sisymbrii

It occurs to me that I may have seen this species previously, but passed it over by confusion with another "early bird" butterfly, the Spring White. When they are in flight it is essentially impossible for an amateur like me to tell them apart. Even the ubiquitous Cabbage White can complicate matters.

Cabbage White, Pieris rapae

I also vaguely recalled seeing another species of marble in Arizona, when I lived there. Luckily, my memory served me well and I was able to locate my one image of the specimen, a Pearly Marble, Euchloe hyantis, from the summit of Tumamoc Hill in Tucson, on....get this....April 4, 2010! The Pearly Marble ranges from southern British Columbia to northern Mexico, west of the Rockies. The males do what is called "hilltopping," flying swiftly along ridgelines to intercept passing females. According to the Kaufman Field Guide to Butterflies of North America, the males are "....fast, erratic....and rarely pause except briefly at flowers." I am glad this one was so cooperative.

Pearly Marble, Arizona

Birders traveling to Alaska and adjacent Canadian provinces might wish to be on the lookout for two other marbles, the Northern Marble (E. creusa), and Green Marble (E. naina). The Green Marble is highly restricted in its distribution, however, so good luck. Still, marbles are unique and captivating insects worth taking the time to observe and appreciate.

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