Wading for Bugs: Exploring Streams with the Experts

1. The Ghost Mayfly

4 1 The Ghost Mayfly John Woodling Anglers and stream biologists know that flowing water and ever-changing rivers create experiences both rare and beautiful. Sometimes they present questions that may never be answered. I remember one foggy evening on July 27, 1969, when Jerry Parsons and I, both graduate students at the University of Louisville, were collecting adult aquatic insects from Brashears Creek in Spencer County, Kentucky. A slight change in barometric pressure created a light fog in the Brashears Creek Valley, bothering what few drivers were out and about. Enough light remained so that we noticed a fog bank rapidly moving towards us, winding through the overhanging trees and shrubs and curling over the stream. The sun had set, and dusk was deepening. To lure flying adults, we’d suspended a white collecting sheet from a tree limb to reflect light from our ultraviolet blacklight lamp. We were hoping to match adults with larval and nymph stages from the stream, but that night the few caddisflies and stoneflies we attracted were the same as others we’d seen for the last few weeks. Without a breath of wind, the fog rolled over and past us. We watched streamers of mist weave through the limbs and leaves The Ghost Mayfly 5 of the pin oaks lining both sides of the creek. Instantaneously the temperature dropped several degrees, although we didn’t feel cooler. It was Kentucky: the evening remained hot and muggy. The flying insects also didn’t seem bothered by the temperature change. Bugs continued to fly into the sheet, creating a light patter of sound as wings, bodies, and legs hit the cloth. We talked idly and drank from our half-gallon bottle of Pisanno, a cheap red wine that accompanied us on those lazy evening collecting jaunts. The fog quieted the few country sounds, though a soft gurgle of water flowing over riffle cobblestones wafted in the swirling mist. Gradually we became aware of faint plopping sounds coming from the stream. Jerry played the beam of his flashlight onto the water. We saw fish rising and feeding on pale white insects that floated on top of the slowly swirling stream. These white wisps were about an inch and a half long with wings only slightly shorter. The white mayflies were emerging to mate, floating down the stream using their cast nymphal husks as rafts while their wings inflated and dried. They were a movable feast for the fish. With a sweep of our butterfly net, we got a few of the first mayflies rising up into the air. They were very delicate and had useless legs that couldn’t support their bodies. To our surprise, this was a species completely unknown to us. Quickly, the numbers of flying mayflies increased, and the sound of fish feeding intensified. Evidently the change in pressure and temperature had triggered a mass emergence of the pale mayflies. Jerry and I completely lost interest in using the blacklight, which didn’t matter since the mayflies weren’t attracted to the light. The mass of flying pale insects formed an undulating tube that floated silently over the stream through the fog, rising and falling from a height of about ten to fifteen feet down to the surface of the stream. Like a ghostly vapor, the entire swarm stayed over the water, never straying past the adjoining stream banks. The pale, silent cloud of life wove through the evening mists, confined by the darkening tree mass along the stream bank. We stood mesmerized by the spectacle. A moment later, many of the mayflies looked like two individuals flying in tandem. As the lead portion of an individual 6 Mayflies in the Mist rose and fell, the trailing part followed like the rear end of a roller coaster. We used our trusty butterfly nets to grab a few. What looked like a pair of individuals hooked together was actually a single mayfly. Because most mayflies are subimagoes, not true adults, when they first emerge from the water, they must molt one more time before mating. What we saw as the front part of the tandem pair was an adult, or imago; the back part was the cast skin of the subimago, which remained attached to the two tails of the adult. These mayflies had only a few seconds to wiggle out of their subimago skins before rising out of the water, assisted...