Yesterday, August 29, 2021, I received an email from C. Croll requesting ID of a moth photographed by T. Ormenyi. Their query read,
“I live on Orcas and kayak quite a bit. Today I was paddling from Patos Island back home, and there were thousands of moths in the air. They were heading from south to north. We first saw them on Patos but then all the way home. Some had fallen onto the water on the crossing. ”
“I had not witnessed so many moths all traveling together before. Seemed like a migration of some sort? When they first arrived I thought there were cottonwood seeds floating on the breeze, took a second to realize that it was moths. The air was full of them for almost an hour. “
These moths sighted by Calvin and Tessa are the Phantom Hemlock Loopers, (Nepytia phantasmaria). They are in the family Geometridae. This species ranges from southern BC to California. There is one generation produced per year and larvae feed on conifers, including Western Hemlock, Douglas-fir, Grand Fir, Amabilis Fir, Sitka Spruce, and Western Red cedar (Bugguide.net).
Adults typically emerge in fall (September and October), so seeing them now is a bit earlier than when I’ve typically collected specimens at my porch light on San Juan Island. Last year, I photographed my first specimen of the season on Sept. 7, 2020. As these moths are nocturnally active, Calvin and Tessa’s report of of them traveling en-masse like this during daylight was intriguing. I was curious to know more.
William H. Hendrix III’s thesis titled Migration and behavioral studies of two adult noctuid (Lepidoptera: Noctuidae) species plus feeding observations of some moths common to Iowa (1990), cites (Johnson, 1969), stating these migration events are part of the “oogenesis flight syndrome” stage where the newly emerged adult insects move en-masse before reproduction and egg laying takes place. Hendrix (1990) also provides some theories as to WHY these moths migrate in the first place. Several theories have attempted to explain this, but he concludes, “Migration, consequently, occurs primarily in young adults and its chief function is to allow escape from unfavorable habitats and allow colonization of a broad range of environments” (Hendrix, 1990).
After reading about this particular species, I believe the migration witnessed yesterday could be attributed to either 1) the sudden weather change we experienced overnight in the islands, or 2) the lack of suitable habitat for reproduction because of the drought we are experiencing. I’m guessing the drought may have more to do with this and we will see more evidence as other species struggle to survive the coming environmental shifts associated with global warming.
Thanks to Calvin and Tessa for sending in their observations!
References and Further Reading
Edwards, D.. (2011). Activity rhythms of Lepidopterous defoliators. II. Halisidota argentata Pack. (Arctiidae) and Nepytia phantasmaria Strkr. (Geometridae). Canadian Journal of Zoology. 42. 939-958. 10.1139/z64-093.
Hendrix, William Hurston III, “Migration and behavioral studies of two adult noctuid (Lepidoptera: Noctuidae) species plus feeding observations of some moths common to Iowa ” (1990). Retrospective Theses and Dissertations. 9373. https://lib.dr.iastate.edu/rtd/9373 https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=10372&context=rtd
Johnson, C. G. 1969. Lepidoptera: Long-distance displacement. In MigrationandDispersalofInsectsbyFlight. Methuen&Co.,Ltd., London. 763 pp.