On the Hunt for Crowberry Blue

By Laura Hatmaker

“Don’t mess this up. Stay calm,” I muttered under my breath, repeating it as a mantra as I slowly and cautiously extended my net ahead of me. My footsteps were measured and knees crouched as I slinked closer. Different scenarios rapidly played in the back of my mind as I neared my target: a diminutive butterfly that flashed brilliant blue when it batted its wings, nectaring on a cluster of nearby Labrador tea flowers.

Author and field naturalist graduate student Laura Hatmaker at work conducting a vegetation survey and natural resource inventory for two MCHT-conserved properties in downeast Maine.

The target of my attention was the crowberry blue (Plebejus idas empetri) a small butterfly in the Lycaenidae family. Taken in profile, the wings and antennae together are no bigger than your thumb. Two black-and-white striped antennae poke out above two jet-black eyes and a predominately white head and legs.  

“My footsteps were measured and knees crouched as I slinked closer.”

As you gaze at its folded wings, the outer scales are mostly an ivory color that fade to a steely light grey at the thorax. Both upper and lower wings are dotted with ebony spots and ringed in a brighter white, each shaped more like a splash of paint than a perfect circle. Along their wing margins, the ebony spots are smudged and ringed in a bright orange before being edged once more in black—a paintbrush dragging along each vein. The outermost margin is further decorated with a delicate sable line that enhances the shape before the wings feather out at the very edge. These traits are identifying markers of the crowberry blue.  

When the butterfly opens its wings, the ivory color and spots are gone, and you are dazzled by a vibrant, iridescent blue that shimmers in colors ranging from brightest azure to royal blue, the back of its body scaled and tufted to match. The black outline from its exterior is mirrored, but the outermost edges remain white, enhancing the dramatic display of opalescent blues.  

“At my particular site, the last crowberry blue sighting had been in the 1990s, and no specimens had previously been photographed or taken for confirmation.”

The black crowberry, which is found in bogs and nestled on rocky outcrops, is the larval host for the rare crowberry blue butterfly.

As with many pollinators, the crowberry blue is highly specialized. Its larval host plant is black crowberry, a plant that nestles in bogs and clings to rocky outcrops. However, this butterfly is even more particular, preferring the coastal plateau bogs found only in Maine’s Washington County. This limited range and sensitive habitat have earned the blue an S2 (Imperiled) species rank in the United States.

This summer, I was working in one of these coastal plateau bogs. At my particular site, the last crowberry blue sighting had been in the 1990s, and no specimens had previously been photographed or taken for confirmation. As part of my study, I was determined to find, catch, and photograph the crowberry blue to validate its presence in the bog.

A daytime flyer on the wing in mid to late June and July, that June afternoon in the bog was a bit early for the crowberry blue. I was not anticipating finding my quarry and had even contemplated not bringing the net with me that day. Yet, serendipity and the stars aligned: I glanced up from my peat-depth measurements just in time to see a flash of deep azure ahead of me, a wink of color before returning to a white spotted tuft—the size of tussock cotton sedge’s apical fluff.  

“I glanced up from my peat-depth measurements just in time to see a flash of deep azure ahead of me.”

Photo by Laura Hatmaker of the crowberry blue butterfly.

I held my net poised under the Labrador tea the crowberry blue was on. Offering a quick prayer, I flicked the net up and over, heart hammering as I peered through the mesh to see my results. Success winked back at me in blue and speckled white, the fluttering form of the crowberry blue secure in my net. Hands shaking in excitement, I took deep breaths to steady myself.  Nerves calmed, I carefully transferred the delicate form to my cellophane envelope to capture a lateral image without touching and irrevocably damaging the butterfly.   

My documentation complete, I released the crowberry blue to the gentle breeze over the bog, watching as it joined with companions I had not previously noticed. A sign of a steady population, they danced around hummocks of crowberry and tufts of Labrador tea.

A version of this story was originally published by the Vermont Entomological Society.

Laura Hatmaker is a graduate student at the University of Vermont – MS candidate for the Field Naturalist program, which she describes as “field ecology, research, and planning meets science communication and education.” In the summer of 2021, as part of her graduate program, she worked as a consulting ecologist in Washington County for Maine Coast Heritage Trust. Give her a follow on Instagram @lhatmaker and Twitter @hatmakerlaura.