Watching Washington Butterflies with Bob Pyle: Number Forty Nine

While many people know about novelist Vladimir Nabokov’s love for butterflies, few are aware of his lasting work on the orange-bordered blues, and fewer yet his other contributions to lepidopterology. Nabokov knew his adopted North American butterflies overall, and at one point contemplated an omnibus work about them, until his literary success took over. It was Charles Remington, his one-time colleague at Harvard and long-time Yale butterfly biologist, who told me about one of Nabokov’s particular insights: he was the first to point out that a substantial portion of North American butterflies (north of Mexico) – maybe 15% or more-are not residents throughout the year but annual (or less often) arrivals from the South. These are our immigrant butterflies, who care nothing for borders, and they are neither very well known nor understood. In this column, I hope to sketch in the basics.

Birders and butterfliers, among other naturalists, have long sought to categorize the species appearing on their respective local, state, and regional check-lists in terms of their status. Their terminology has never been standardized, but certain terms have been used repeatedly. “Resident” refers, pretty unambiguously, to those species that occupy (let’s say) the state all year round, every year. (For birds, the picture is complicated by the many annual migrants, so now we will narrow down to butterflies.) We assume, no doubt correctly, that these species comprise the largest part of our list, and for the most part we know the life stage in which they overwinter-pupae for swallowtails, eggs for many blues, adults for anglewings, for example. In order to be a resident up here in the seasonal North, these species must possess a winter diapause-the ability to modify metabolism in order to make through periodic freezing temperatures, akin to a winter hibernation, involving antifreeze substances in their cells.

After “residents”, faunists have employed a battery of terms to designate degrees of residence: visitors, vagrants, strays, migrants, immigrants, accidentals, apocrypha, and so on. None of them is entirely satisfactory for all cases, and each carries differing connotations. Our only true, birdlike, back-and-forth migrant in the strict sense, involving the whole population every year, is the Monarch, and perhaps the Painted Lady to a lesser and evolving degree. When a Monarch shows up in Western Washington (under its own steam), outside the range of milkweeds, it might fairly be called a “stray”. Purposeful turn-outs, like wedding Monarchs and school Painted Ladies, are dubbed “releases”. Species that arrive by inadvertent introduction, such as a chrysalis on a camper or boxcar, as seems likely with our sole records for the White Admiral and the Zebra Longwing; and lab, hobbyist, and butterfly-house escapees can be called “accidentals”, probably including the recent Atlas Moth found in Bellevue and a cluster of Queens at Tri-Cities. Fortunately, these last two categories usually prove ephemeral. But when species non-native to North America become established, we called them “introduced” or “naturalized”. We have two of these, the Cabbage White and the European Skipperling. All our other species, resident or visitor, are considered “native,” or “indigenous”.

And then there are Nabokov-s 15%: the species that arrive with us annually or less, either in numbers or as ones and twos, that are part of a general northward diaspora undertaken by that species in the early southern spring. These movements vary greatly in strength and reach depending on both weather and climate as well as traveling conditions and other factors. They tend to leap-frog or hop-scotch in repeating, rapid generations, flying close to the ground and exploiting the wind, and very often following watercourses and other way-routes north, in a process known as saltation. Rivers and roadsides are frequently where their weedy hostplants and nectar sources are to be found. I consider the best terms for these incomers to be “immigrants”, for obvious reasons, and “irruptives”, because they burst out of their subtropical or temperate headquarters in a population explosion or mass movement known by biogeographers as an irruption. Some of these irruptions, such as those of Snout butterflies and giant sulphurs, can be truly dramatic, involving millions of individuals over days of passage.

Others are much more subtle-a barely noticed ripple of tiny butterflies over the landscape, building up as they go. These butterflies do not possess a winter diapause, though they can be quite cold-tolerant and last up to serious frosts, and they are generally one-way affairs, as far as we know (though recent radar imaging has revealed much more return flight for Painted Ladies than we had ever imagined). We should note that there are also mass movements among the residents, such as the well-documented (Pelham and James) altitudinal shifts of Coronis Fritillaries, and the unpredictable blastouts of California Tortoiseshells. These comprise a different subject.

It so happens that, as I write, we find ourselves at the very climax of one of the most spectacular instances of irruptive arrival in the history of Washington butterfly study. Back in the fall of 2004, following a tip from Neil Bjorkland and a challenge from Andy Warren, I sought and found the first Pygmy Blue recorded in the state (see G’num 12 (1) February 2011). Only a couple had been spotted since…until early this September, when birder Chris Linsey photographed one along the Walla Walla River, Mike Denny passed on the news, and a flood of observations followed. David James conducted a field trip on which dozens of observers spotted and photo’ed hundreds of individuals flashing their tiny brilliants around their beloved Russian Thistle (aka tumbleweed). D. James has monitored them since, expecting them to crash with the weather around Halloween. This has been a true phenom, greatly raising interest in our immigrants.

So, who are they, and what is their M.O.? Why would they come all this way, only to die off in the cold? Please under- stand that much of what can be said on this score is only informed speculation, since we seldom possess definitive data and must rely on likelihood. This involves human judgment, so reasonable people are bound to arrive at different conclusions (as RMP and JPP certainly have on some of these issues and species!). My criterion is that if we possess one or more verified, reliable records for a species in the state, and if it is a known, regular irruptive with any known appearances in adjacent or nearby states or provinces, then I count it as such here as well. So here we go:

• Northern White Skipper: Might or might not be resident, known to emigrate out of the South. Showed impressive numbers in certain locations in Washington this year.
• Common Checkered Skipper: Long assumed to be resident, but considered an annual immigrant in the Northeast. Do we know for certain about the Intermountain West?
• Sachem Skipper: Was an irruptive arrival in the nineties; likely resident now-see below.
• Checkered White: rare immigrant, possibly increasing, a cluster of sightings in 2022.
• Orange Sulphur: Dr. Orley Taylor, migration specialist, considers it an annual arrival in the North, with no winter diapause. Invades the high country from the eastern alfalfa fields in summer, then down into western Washington each summer and fall.
• Dainty Sulphur: major northward thrust each year from TX/MX/AZ/SoCal, mostly into the Rockies and Midwest, with some reaching the corners. I found the first in WA in 1975, seven fresh males on Snake/Grand Ronde rivers in Asotin Co. None since, but others in region that year. Long-term study suggests close fidelity to river systems in movements.
• Pygmy Blue: see above. Major movement elsewhere in the West this year as well.
• Reakirt‘s Blue: One pair caught near Ellensburg in 1993 by Joe Albright. A well-known annual irruptive through much of the interior West, almost as small and easy to miss as Pygmy.
• Variegated Fritillary: Regular and major annual emigrant from subtropical Americas into Rockies and beyond. J. Bauman and C. Rogers had the first WA sight records, RMP caught a voucher in Okanogan Co, in 2017.
• Buckeye: common immigrant in S. Oregon, several recent sightings and photos in Washington; famed irruptive species on both coasts.
• Painted Ladies: All four species probably immigrate each spring, in wildly varying numbers, from road-blocking to nearly none, with also varying survivorship in milder winters.
• California Sister: occasional visitor; as with many immigrants may breed before dying back, but no records of it.
• Monarch: our one actual annual migrant, well documented each year by D. James.

If all these are in fact visitors, and doubtless I have missed others, that would be about 10 % of our known fauna. The number is higher farther south and central, and along the East Coast; at Cape May, New Jersey, the autumn butterfly movement can be almost as impressive as that of the birds. Naturally, fewer venturers reach the far corners of the country than the Heartland.

Exciting to me, as a biogeographer, is the question: what further species might we record presenting their credentials at our state line? Among the regular irruptives that point in our direction and might fetch up here eventually are: the Mexican Yellow, the Sleepy and Tailed Oranges, the Cloudless Giant Sulphur, the Marine Blue, the Great Purple Hairstreak, and the Snout. These and others are regular movers elsewhere in the West and might well appear.

Any discussion of immigrants raises the question, how can we be sure a species overwinters or not? And the only answer is, short of finding them in midwinter in one stage or another, we cannot. Even early spring appearance sightings do not prove overwintering, as the exodus from the South can begin in late winter and progress remarkably fast, when weather, nectar, moisture, winds, and other factors are all favorable. Merrill Peterson and others will be trying to determine whether Pygmy Blues will remain with us this winter or not, after so many arrived. Though they have never been shown to overwinter north of San Francisco Bay, to my knowledge, and that fitfully, it is certainly possible, if the â’22-23 winter is mild in Walla Walla. But it is difficult to demonstrate. Scanning the always-increasing iNaturalist reports can suggest whether they are showing up to the south of here or not. But keep in mind: the expanse of territory these insects are navigating is absolutely vast, they are minute, and observers are few and far between. So, it‘s a classic case of collecting bias: and, as every beginning biogeographer knows, absence of evidence does NOT suggest evidence of absence.

So why DO they do it? Why leave the nice warm South, to face cold winds and rain for mile after bleak mile over the vast American land, only to endure a frosty end for your grandchildren in the frigid North? BECAUSE all species always try to push the edges of their ranges, a little or a lot. And while specialists need to keep quite close to home for their particular needs to be met, generalists such as our immigrants-with many weedy hostplants and high reproductive capacity-can afford to absorb a lot of loss along the way. If they manage to expand their year- round range just a little, it will all be worth it. They are betting on the come, as they say in Vegas: you might not have what you want right now, but you are hoping you will when you really need it. Or in Darwinian terms, natural selection will pay off with a jackpot under the right conditions. That’s why!

And what are the right conditions? Climate change, for one. In a time of warming climate, species that push the boundaries will be well situated to benefit over time. And, of course, that’s where we are right now. While warming trends may push our rare arctics off the mountain tops, they should favor all of these irruptive species, both by permitting them to survive farther and farther north, and in some cases actually to evolve a winter diapause. We have observed this transition in the Sachem skipper. A well-known immigrant in the West for decades, it made its appearance in the Willamette Valley in the mid-60s, Portland in 1986, Vancouver, Washington in 1990, and in Spokane county just this year. And through the research of Lisa Crozier, largely in the Tri-Cities, we know that it has not only followed (even preceded) the warmer temperatures north, but also adapted to overwintering in colder climes-graduating from immigrant to bona fide resident status. Who knows? Maybe Merrill will discover that the Pygmy Blue will be the next such winner.

As average temperatures rise even more, we are bound to see an increase in these movements. I predict that we will have additional sightings of each of the irruptive species named above; that they were not “accidentals,” but vanguards-advance signs of things to come, showing the art of the possible for these creatures elegantly adapted to take advantage of change. The time will come when Pygmy Blues and Dwarf Yellows are regular members of our fauna, even if Asotin County is largely uninhabitable for humans by then.

Meanwhile, I urge all Washington butterfliers and birders-gone-bad to take themselves down out of the lush mountain meadows and out to the rabbitbrush edges, the tumbleweed hedges, and other uninviting barrens and wastes along our long southern border; and to keep both eyes out for unfamiliar butterflies busting out from their southern realms, up into our latitudes. You just might spot the signs of things to come.

NOTE: None of the rhetoric in this piece is meant to imply any political comparison with humans, though the shared terminology makes such assumptions almost inevitable. Humans cannot fly, and for them, unlike for butterflies, a border is a very real thing.

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