Watching Washington Butterflies With Bob Pyle: Number Two

I’ve just come in from cutting Scots broom in a neighbor’s fields, once productive dairy pastures but now fallow and taken over almost completely by reed canary grass, blackberry, and broom. It was hard, hot, sweaty and stickery work, but satisfying. These bottomlands are not likely to be fully indigenous again in my time, but by reducing the opportunistic broom, at least I am helping to give willows and other native plants a chance to gain a foothold.

If you’re like me, you take special pleasure in habitats dominated by native organisms. It is more fun to watch western gray squirrels than eastern, a Lewis’s woodpecker than a starling. This is not much of an issue with butterflies themselves in Washington. The only two exotics we have are cabbage whites and European skipperlings. I actually appreciate Pieris rapae for often being the only butterflies to be seen in many times and places, especially in Western Washington. I have to say I admire their adaptability and the way they have occupied many of our seashores, right down to the tideline, by colonizing beach radish or sea rocket (Cakile maritima and C. edulenta). As for Thymelicus lineola, we watch its slow spread along our northern borders with interest, and with some trepidation, in case it might disadvantage our uncommon native skippers in the high meadows of the Pend Oreille. In 2008, I found it by the tens of thousands in the Little Blackfoot country of Montana, and no woodland skippers, the usual common species at that season, at all; so there may indeed be cause for concern over European Skipperlings. But on the whole, when among butterflies here, you are among natives.

Not so with plants. Hundreds of species have been introduced, on purpose or inadvertently, and many of these have become all too well established. Who among us has not noticed roadsides dominated by Herb Robert, even in wilder corners of the Olympic Peninsula; riversides all but consumed by Himalayan blackberries or Japanese knotweed; and formerly diverse grasslands shot with cheatgrass? We have hundreds of examples. Thea and I visited a handsome place east of Missoula along Rock Creek, known as the Valley of the Moon, and concluded it should be called the Valley of Knapweed; ditto, now, for much of Okanogan County. Then there is Scots broom, the shrub that ate the West. So whenever we look around and find ourselves surrounded largely by indigenous herbs, shrubs, and trees, it gives us a special frisson of delight, a good, things-as-they-ought-to-be feeling. It’s a sensation that is all too rare.

Given the presence and abundance of Eurasian plants adapted to our land (the word “our” written by this person of European descent not without irony), I find it interesting to ask how our native butterfly fauna responds to a flora with which it did not evolve. As a life member of the Washington Native Plant Society, I would like to think (as many choose to believe) that our butterflies actually prefer native plants when it comes to larval hosts and nectar sources. I would love to be able to reinforce that belief, but in all honesty, I cannot. Yes, anise swallowtails used mostly yampah in California, lomatiums in the Columbia Basin, and angelica by the sea before we came. But these days they exploit weedy fennel just as happily in alleys of the Central District of Seattle and along the highway verges. Two-tailed tiger swallowtails are much more abundant across the arid West today for having adapted to green ash shade trees for their larvae, and thistles, teasel, knapweed, and other weedy composites for nectar. Silvery blues proliferate on pink Vicia sativa along I-5, and purple Vicia kracca in the Blue Mountains. Spring butterflies like orangetips and arriving ladies love dandelions, while Clodius parnassians and most species on the wing in mid- to late summer nectar above all on hairy cats-ear (Hypochaeris radicata). Among the most awkward examples of such adaptive shifts toward exotics: the recently rediscovered island marble on San Juan Island, which escaped extinction by feeding on introduced, weedy mustards in lieu of their original larval hosts, whose identity is uncertain; the federally threatened Oregon silverspot, which in some sites got by on tansy ragwort in the absence of native nectar sources; and West Coast winter monarchs roosting mainly in Eucalyptus trees, ever since their original California coastal forests became too fragmented for them.

Does any of this, or the many other examples we could name, mean that we should embrace these exotic, adventitious plants, and abandon our efforts to remove them from native habitats? Certainly not! The negative impacts of noxious plants on indigenous communities and organisms are great and irrefutable. But it does suggest that if we aspire to get rid of weeds that our butterflies have dilemma of butterfly bush. Any readers who try them out, please let us all know how they do! Butterflies, it turns out, do not know native from learned to use, it would behoove us to think about their needs in advance, and take measures to replace the missing resources with native species of equivalent utility.

Lepidopterists face a special challenge in this regard. Butterfly bush (Buddleja davidii) has always been considered the most valuable and attractive of all butterfly garden nectar plants, native or non–distinctly non, in its case. As long as it was confined to yards or waste areas, BB could be enjoyed by butterflies and butterfliers alike without attendant problems. But the situation has changed as Buddleia has escaped into a benefits of our latter-day plants, when it comes to the number of habitats dominated by native plants, primarily riparian. Riverbars and certain seral forest stands are proving especially susceptible to colonization by butterfly bush, which has been listed as a Class B noxious weed in both Washington and Oregon. This places a strong onus on butterfly lovers, especially those who also love native plants, as most of us do: if we choose to utilize BB in our butterfly gardens, we take on the heavy responsibility to deadhead the blooms before they broadcast their copious seeds in late fall, as well as to police our perimeters and make sure we are not the source of any outbound colonization. If, instead, we choose to eliminate Buddleia, our imaginations will be taxed to come up with replacements both native and anywhere near as attractive. Our favorite native, late season nectar source where we live in Southwest Washington is Douglas aster. You may discover others that work well where you live.

Meanwhile, according to the Oregon Department of Agriculture, “effective immediately, the propagation, transport, purchase, or sale of butterfly bush (Buddleja davidii) is prohibited in Oregon with the exception of sterile varieties that produce little or no seed.” As our president Al Wagar remarked to me, “Sterile varieties of Buddleja seem a lot safer than depending on people to remove and destroy seedheads. Among thousands of gardeners, change of ownership, personal mishaps, and so on would surely result in many escapes.” I agree; and, of course, who is going to deadhead the existing feral stands? If these seedless varieties and hybrids retain their nectar and astonishing attractiveness for butterflies, they may furnish the answer we’ve needed for the vexing dilemma of butterfly bush. Any readers who try them out, please let us all know how they do!

Butterflies, it turns out, do not know native from non-native. But we do, and if we take pleasure in places where the flora and fauna more resemble what David Douglas found here than the tossed salad we have made of things since, it is up to us to do our part to help keep the landscape that way. We can and will enjoy the accidental benefits of our latter-day plants, when it comes to the butterflies that employ them; but we should also do what we can to maintain and restore the natural communities that arose here without us.

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