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.

Spring White

Fashion rules dictate that one cannot where white after Labor Day, but the Spring White butterfly, Pontia sisymbrii, need never worry. These pale insects expire long before that arbitrary deadline. Indeed, these are among the first butterflies of spring here along the Colorado Front Range, often appearing before the official date of the spring equinox.

Heidi and I have seen several specimens already this year, on March 9, along the Arkansas River below Pueblo Reservoir. I expect to see them any day now here in Colorado Springs.

These are wary butterflies that perch frequently but startle easily. Approaching one to take its photograph is usually an exercise in futility. Males are known to “hilltop,” flying along the tops of ridges and buttes to intercept females flying up from below. You can also find them in canyon bottoms, the topography funneling females into those areas.

Like most members of the family Pieridae, caterpillars of the Spring White feed on cruciferous plants: mustards and their cousins. Females deposit one egg at a time on the stems and foliage of host plants, especially hedge mustards (Sisymbrium spp.), tansy-mustard (Descurainia spp.), and rock-cresses (Arabis spp.). In some places in northern California, Brewer’s Jewelflower, Streptanthus breweri, produces orange spots that mimic the eggs of the butterfly. The female insect avoids those plants, since caterpillars are known to cannibalize each other when too many are on one plant (Pyle, 2002).

The caterpillars hatch from the eggs in roughly a week and begin feeding in earnest. The larvae progress through five instars (an instar is the interval between molts, first instar being what emerges from the egg), and older caterpillars are quite attractive as you can see in the image below, shot by Aaron Schusteff and borrowed from Bugguide.net

© Aaron Schusteff via Bugguide.net

At the end of the fifth instar, the caterpillar graduates to the pupa stage. The chrysalis is described as being mottled brown or black with a granular texture. While the chrysalids of most pierids are each suspended in a “girdle,” a belt-like strand of silk around the midsection and attached to the substrate at two points, the Spring White pupa lacks this feature. It attaches to the surface of the leaf, stem, or other object only at the tail end of its body. Hooks fasten into a tiny pad of silk to secure it firmly.

Some specimens have a nearly pure white upper surface

This butterfly ranges over most of the U.S. west of the Rocky Mountains, including the mountains of Arizona and New Mexico, spilling over the divide into extreme western South Dakota and the panhandle of Nebraska. It also occurs in south-central British Columbia. In Oregon and Washington it is found east of the Cascade range (and in the mountains of the Olympic peninsula in Washington).

Look for this species early in the season, from late February on through the end of June. It frequents foothills and higher elevations. It flies earlier than most whites, but pay attention to the dark pattern of veins on the underside of the hind wings to cinch an identification.

The Spring White may be a more accurate predictor of the arrival of spring than Punxsutawney Phil, the famed groundhog, at least here in the western U.S. Good luck getting the butterfly to pose for a photo opp, though.

Sources: Brock, Jim P. and Kenn Kaufman. 2003. Kaufman Field Guide to Butterflies of North America. Boston: Houghton Mifflin Company. 384 pp.
Lotts, Kelly and Thomas Naberhaus, coordinators. 2014. “Spring White,” Butterflies and Moths of North America.
Pyle, Robert Michael. 2002. The Butterflies of Cascadia. Seattle: Seattle Audubon Society. 420 pp.