Nettles and Their Butterflies in a Frenetic Spring

Watch a nettle emerge from the spring soil and tell me it doesn’t remind you of a butterfly crawling from its chrysalis. The plant appears as a bulbous bundle of leaves, pointed at the tip, purple-green, and soon peels back to spread its first leaves like wings.

As the weeks pass it will repeat the trick again and again, extending its stalk, each pair of leaves coming out perpendicular to the pair below, like mint leaves.

Visions of soup, pesto and tea dance in my head as I await the nettle flush. At last, fresh-picked greens return to our diet.

So it threw me this spring when the flush froze. For weeks the chrysalises waited, refusing to open. It made me wonder: how do plants deal with spring’s frenetic weather?

After the long deep freeze in mid-January, temperatures zoomed up and twice tickled 60 degrees. On many plants, buds began to swell. A fat overwintering bumblebee stumbled around our porch. I found a few red-flowering currant buds that had split and showed the tiny, shriveled leaves within.

Then February brought a return of typical winter weather: mid-40s and rain. The swollen buds ceased to swell. Arrested development. Days slowly lengthened. Nettles appeared on schedule in mid-February. Then we had the coldest start to a March since the 1980s. Titanic snowflakes mixed with rain and several nights froze hard. The nettles ceased to grow. Would they die back? All around, plants had been putting forth their most tender and water-filled parts. How do they survive when spring weather plays hot and cold?

March finally warmed, and the nettles went right back to growing. Insects emerged. By April Fools’ Day, we’ll be seeing showy wildflowers on osoberry, red-flowering currant, salmonberry and evergreen violet. And still, it might freeze. For such understory plants, spring offers reward and risk. If a plant can leaf out earlier than the alders and maples above, it wins several weeks of unblocked sunlight to kickstart its growth. Its flowers, in the fleeting hours when clouds scatter, are warmed and made fragrant by sunlight that will be dappled at best when the big trees get going.

The stakes are high. In many species, the leaves will die back during a late-spring cold snap. The plant must marshal its reserves to try again. Some cannot and die. There is a whole field of research, fascinating to me, that studies spring growth, its timing, what triggers it.

On woody plants, buds form in fall. Buds are packages of growth cells tightly protected against winter weather. The single prompt telling a woody plant to drop its leaves, form buds, and generally harden off for winter is photoperiod, the length of day, which makes sense because these things take time and must happen in advance of freezing temperatures.

In spring, however, the trigger for renewed growth is more complicated. It depends on the species and remains only partially understood, but it seems to be a complex blend of photoperiod, temperature and the number of chill hours accumulated over the winter. Even one species can show a variety of timings. Think of big-leaf maple. Come Earth Day, when the woods are flowering with dogwood, Oregon grape and bitter cherry and insects are abuzz, half the maples are draped with a million flower clusters and no leaves, a quarter are all leaves and no flowers, and a quarter have both. It’s all about hedging bets.

The timing of these things matters. Hatches of caterpillars are timed to give them maximal time on young leaves, which are more nutritious and less chemically defended than older leaves. Spring migration of insect-eating birds is timed to coincide with insect hatches.

In Concord, Massachusetts, the detailed nature journals of Henry David Thoreau have given naturalists the ability to compare spring’s timings in the 1850s with those observed today. The 43 species tracked by Thoreau are leafing out 18 days earlier, on average. Insects have shifted their timings but not fully, and birds are lagging more. Naturalists worry that some migratory birds are now missing the peaks of their insect food sources.

The study of timings is called phenology. To me, it is terribly exciting. For anyone with the patience to take notes, a whole symphony of reverberating blossoms is waiting to be heard.

Back to nettles. Are they appearing earlier in spring? It remains to be studied.

Nettles grow in damp shady places, often seeming to prefer churned soil. To me, the classic image of Key Peninsula nettles is a dense stand of them on an abandoned logging road, alders overhead. Their buds form underground, part of the unseen “bud bank” that gives a landscape much of its power to regrow after disturbance.

Nettles, believe it or not, are one of our most important host plants for moths and butterflies. Pollinator-friendly flowers may get all the press, but butterflies are just as dependent on the plants their caterpillars eat, and many species are quite specialized — you won’t find them away from their caterpillar host plants. In his excellent field guide to the butterflies of Cascadia, Robert Michael Pyle writes, “People denigrate native nettles as noxious weeds due to their sharp sting. By eliminating them, they exclude three of our most attractive butterflies that might otherwise be common even in town.”

The first of the three is the red admirable, a big showy butterfly with red bands and white speckles on its brown wings. Winston Churchill is said to have prevailed upon his gardeners to let nettles be for this butterfly, which has a habit of landing on gardeners while they work. Vladimir Nabokov called it “a most frolicsome fly ... with an almost frightening imitation of conscious play.”

Nettles also support Milbert’s tortoiseshell, a mottled brown thing that flashes orange when it flies, and the satyr anglewing, which looks like a broken leaf at rest. Look for them. Look for their caterpillars on nettles and let me know what you find — I’d love a better sense of the nettle-dependent lives here.