Research Spotlight: a New Method of Searching for Rare Butterflies

by Josh D. Kouri || Photos by Bryan Reynolds

How do you find a rare, tiny, well-camouflaged butterfly that’s only active for a few weeks each year? That’s the question that Bryan Reynolds and other researchers studying the frosted elfin butterfly (Callophyrs irus), a species of conservation concern, are asking themselves. Wouldn’t it be easier if the butterflies held up a flashing sign to say, “I’m here,” alerting the researchers to their presence? In a way, that just might be possible.

Frosted elfins are small butterflies in the family Lycaenidae. They can be found across the eastern United States but are rare throughout most of their range (especially in Oklahoma, the western edge of where they can be found). Because of their rarity, and recent declines in known populations, the US Fish and Wildlife Service is investigating this species to determine if it should be protected under the Endangered Species Act. This task comes with plenty of challenges, as the butterfly is both rare and elusive. These butterflies are tiny, with a wingspan of only an inch, and have a dusky brownish-gray coloration that blends into the background and makes them difficult to find even at locations with known populations. Thankfully Bryan Reynolds, one of Oklahoma’s butterfly experts and the man tasked with leading the field surveys in Oklahoma, is up to the challenge.

Frosted Elfin, Callophrys irus, female on larval food plant, yellow wild indigo, Baptisia sphaerocarpa

Reynolds is a professional nature photographer, and since moving to the state in 2005 he has made it his mission to photograph all of the approximately 200 species of butterflies found in Oklahoma. The expertise he has developed during that time made him the natural choice to lead the search for this elusive species. One of his initial ideas was to first locate the frosted elfin’s host plant (yellow wild indigo, Baptisia sphaerocarpa) and then search for the butterflies. Unfortunately, while the host plant has distinctive yellow flowers that make it easy to find, the adult butterflies are only active during a brief period from late March to mid-April, before the indigo flowers. That meant Reynolds would have to find suitable habitat after the butterflies were already dormant, get permission from landowners to survey the sites, then return the following year in the hopes of finding a population of frosted elfins during their brief period of activity.

Frosted Elfin, Callophrys irus, caterpillar on yellow wild indigo, Baptisia sphaerocarpa

Fortunately, when he returns to the survey sites this spring he’ll have a new tool in his arsenal. Recent research has found a way to finally make these drab butterflies stand out: searching their host plants with a UV light at night makes the caterpillars practically glow in the dark! David Moskowitz, a researcher in New Jersey, demonstrated in a 2019 survey that the caterpillars of the frosted elfin fluoresce under UV light (a phenomenon where molecules in the caterpillars’ skin react to the UV light in a way that makes them appear to glow). In these surveys, up to 7-times as many caterpillars were found at night using these methods as could be found using traditional survey techniques during the day.

Photos from Moskowitz (2019), Journal of Insect Conservation

While it was too late in the season for Bryan Reynolds to test out this new technique last year, he nonetheless demonstrated proof of concept during nocturnal searches for other arthropods. The photo of the striped bark scorpion (below) shows just how promising this new technique can be. Reynolds is hopeful that this efficient search method, combined with the host plant’s success in disturbed areas, could reveal more abundant populations of frosted elfins than expected.

Striped Bark Scorpion, Centruroides vittatus, under blacklightYellow Wild Indigo, Baptisia sphaerocarpa