Watching Washington Butterflies With Bob Pyle: Number Eight

It is no secret to any Washington butterflier that we do not exactly live in Butterfly Nirvana. Oh, those east-side canyons can be awfully good in May, and the subalpine Cascades and Olympics in July or August may throb with four-winged color, not to mention the Blue Mountains and the Okanogan. But for much of the time, over much of the state, especially on the West Side, butterfly abundance and diversity are all too noticeably subtle, if not absent. Now, why is that? On first examination, our rich array of plants and habitats would seem to offer great amplitude for dependent Lepidoptera, and so they do. But I don’t know anywhere else where one has such a good chance of walking into seemingly inviting habitat, only to find it depleted, or even entirely innocent of butterflies. Lepidopterists from out of state often comment about this fact, shaking their heads in wonder at finding themselves skunked in such a butterfly barrens. I just shrug, and say, “Well, it is Washington, after all!”

We can easily list the proximate factors for butterfly scarcity in many places: development, chemical spray, overgrazing, or other human activities that diminish habitat quality; extensive rainfall, fog, and cool temperatures during the flight period; the relative youth of flowery pastures and other open areas (usually less than a century since release from forest cover), allowing insufficient time for maturation of habitat and concomitant development of a fauna such as Britain’s ancient grasslands have acquired. But even where no obvious cause applies, and various species do in fact occur, their number is often few and unreliable from year to year. Is there something else going on here?

I have long considered it part of my life’s work to come to a solid understanding of the modest butterfly numbers and variety in my adopted homeland–sort of a Unified Field Theory of Western Washington Butterfly Crappiness. I think I am getting close. Apart from the causes listed above, and the fact that we live well out in the biogeographical corner of the country, one further element rises to the top of my hypothesis. I call it The Rot Factor.

The breakthrough came when Jonathan Pelham quipped to me one time years ago, “Are you still down there studying those mold butterflies?” Something clicked, and I realized he was right: the few species of butterflies that manage to thrive here in the temperate rainforest must somehow cope with extreme rainfall, and the molds they sponsor: hence, the Rot Factor.

You see, butterflies do well in terms of abundance and diversity when conditions are hot and dry (desert), cold and dry (arctic), or hot and wet (tropics); but they do poorly in zones that are cold and wet–like ours. I believe that is because they can survive long, very cold but dry periods in winter diapause, or extended hot and dry periods by aestivating; while in the tropical rainforest, continual broods dispense with the need to diapause. Whereas in the Maritime Northwest, some life stage has to make it through the cool, damp, mold-inducing months of winter; and whether that be egg, caterpillar, chrysalis, or adult, its chances are much reduced by the adverse climate.

I suspect that a great deal of mortality occurs during the moist months, even more so when our wet winters stretch into spring, as happens all too often, such as the “spring” of 2011. This explanation could help to account for why species that occur here right enough, such as Mourning Cloaks, do so in small numbers; while over on the dry, cold side of the Cascade Crest, they abound. The extensive willow brakes near the coast should, it seems, be great habitat for Nymphalis antiopa. In reality, they appear in such locations only sparsely. This pattern appears to repeat itself in Europe. In Great Britain, N. antiopa is known as the Camberwell Beauty, having once shown up in some numbers in the village of Camberwell, now a London suburb. On the whole, Cloaks/Beauties are exceedingly rare in Britain, with its Pacific Northwest-like climate; but much more common on the drier Continent. Perhaps we share the Rot Factor with the perennially damp English, just as we do our regional preference for India Pale Ale.

The inhibiting effects of a cool, damp winter increase, I believe, in direct proportion to the actual rainfall in a given district.  For example, a relatively arid location such as Seattle (average precipitation ~ 37 inches) has less rot (hence more butterflies) than Forks, in the Olympic rainforest, which may receive 150 inches of rain or more. Here in western Wahkiakum County, where I have been struggling for over thirty years to record fifty species of butterflies, precipitation ranges from 110-120 inches; yet just twenty miles to the east, the county seat of Cathlamet receives less than eighty inches. That makes a difference for the butterflies. There seems to be a ceiling somewhere right around eighty inches that limits the westward expansion of some species along the Lower Columbia River valley. For example, Sara Orangetips occur in the eastern part of the county, but not the western; ditto for Silvery Blues. The same is true for a number of plants, including poison oak and ceanothus. Also, some species may be found on the Oregon side of the Lower Columbia, where the rainfall remains at or below eighty inches, but not on the rainier northern shore of the river. An example would be the Ochre Ringlet, common in Clatsop County, Oregon, but virtually absent from Pacific County, Washington.

Happily, certain species have adapted well to the Rot Factor, and manage to thrive in Western Washington in spite of all that our sodden rainforest winters can throw at them. The most successful of these include the Woodland Skipper, the Clodius Parnassian, the Western and Pale Tiger Swallowtails, the Margined and Cabbage Whites, the Purplish Copper, the Echo Azure, the Mylitta Crescent, and Lorquin’s Admiral. It would be interesting to know their anti-rot strategies.

The Rot Factor is a function of both precipitation and temperature, so it can be ameliorated by warming trends. For the first decade and a half I was here, we found the Common Wood Nymph only east of the Gray’s River Divide (our local version of the Cascade Crest, separating the drier east and wetter west sides of the county). Then in the hot, sunny summers of the early 1990s, Cercyonis pegala began to appear on the west side of K-M Mountain: the first was caught by a 4-H insect club member, Katriina Ervest. These days, wood nymphs flip-flop over our yard every August. So this species apparently jumped the Rot Factor to expand. It should be expected that if climate change continues to elevate our average temperatures in winter, or cause drier conditions, the Rot Factor will diminish in influence. But, if repeated La Niña years cause even wetter winters and springs, the R. F. may only exacerbate, along with its challenges for butterflies. Even if they make it through the bleak midwinter alive, butterflies must be able to fly, feed, mate, and oviposit when spring finally arrives, or all is lost.

Though many butterflies (including those subject to rot, like Mourning Cloaks and, I suspect, Milbert’s Tortoiseshells) possess the antifreeze necessary to withstand deep winter, such hiemal survival depends upon staying dry. We certainly have more frosts here now than when I wrote Wintergreen in the early eighties, and nothing trumps the Rot Factor like very wet weather followed directly by a frost– which is what befalls overwintering Monarchs in Mexico when they get soaked by heavy snowfall, then succumb when the temperature drops below freezing. So even global warming might not bring relief for starved West Side butterfliers, unless it produces a combination of conditions inhospitable to the molds and other agents of death and decay that attack the helpless winter stages of our butterflies. It may be that until Metasequoia and ginkgos once again grow at Vantage and Seattle resembles the Neotropics, we will be stuck with our faithful Mold Butterflies. It could be worse.

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