Studying Moths in the North Cascades

September 29th, 2017 | Posted by in Naturalist Notes

By Nick Engelfried, graduate student in the Institute’s 16th cohort

To my mind, it isn’t truly spring in the lush, green landscape on the west side of the Cascades until the first half-white carpet moth (Mesoleuca gratulata) has flown. This small insect, with its delicate wings of white, gray, and dark brown, is a sign that sunny days and warmer weather have finally arrived.


Mesoleuca gratulata. Illustration by Nick Engelfried

I chose the hundreds of moth species in the North Cascades as the subject for my in-depth study of a natural history topic at North Cascades Institute this spring. I was drawn to moths partly because of their vast diversity—there are some 11,000 species in North America, far more than the 750 or so butterflies—and partly because of how deeply underappreciated they are. If you spend time outside in western Washington, you’ve probably seen an M. gratulata at some point—but most people who take time to notice it at all will likely mistake this day-flying moth species for a small butterfly. Most moths are even less noticed, due to the nocturnal habitats, nondescript colors, and tiny size of many species.


Platyprepia virginalis. Illustration by Nick Engelfriend

This spring, I embarked on a project to seek out moths wherever I could: below lights on the outsides of buildings after dark, hiding on the bark of trees and walls by day, and—for day-flying species—flitting across trails in patches of sunlight in the North Cascades forest.

I identified as many moth species as possible, including those I found this spring as well as specimens collected last summer and fall. I relied on Jerry A. Powell and Paul A. Opler’s excellent reference book, Moths of Western North America, as well as the expertise of editors at the citizen science website Butterflies and Moths of North America (BAMONA).

In addition to seeing as many species as I could myself, I generated a list of all moths from eight target families reported on BAMONA from Whatcom, Skagit, Okanogan, and Chelan Counties. This list includes nearly 150 species. For reasons of feasibility, I confined myself to “macromoths,” largely ignoring the smaller and even more numerous but very tricky to identify “micromoths.”

One of the most rewarding parts of studying moths this year has been following the emergence and disappearance of different species as their “flight periods” come and go. Most moths in the North Cascades live in this region year-round, but for much of this time they reside only in the egg, larva, or pupa stages. The length of the adult phase ranges from months in species like the tissue moth (Triphosa haesitata)which overwinters as an adult and emerges to fly in very early spring—to only a few days in the giant Ceanothus silk moth (Hyalophora euryalis), which lives just long enough as an adult to mate and lay eggs.

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