Michigan Trout Unlimited
MICHIGAN Trout
Which Fly Is It?
14
by Ann R. Miller
Summer 2021
As fly fishing transitions from familiar spring hatches of mayflies, caddisflies, and stoneflies to summer terrestrials, it is still important to have an understanding of the insect fauna on streams and rivers. Summer fly boxes are filled with plenty of big floating patterns, many with legs and foam, but let’s consider an insect that is largely a mystery, at least to anglers—the water snipe fly, Atherix lantha. But first, a digression. Terrestrial insects become critical in the diet of trout, helping to sustain them mid-summer through fall. Fly fishers are generally aware of many of these food sources, including grasshoppers, crickets, beetles, ants, inchworms, and more. There are a plethora of scientific studies that have documented which insect is eaten, when it is eaten, and what percentage of the diet consists of any given insect. However, one group of insects that is a little vague on details is Diptera, or true flies. Trout do eat them, both larval and adult forms, but other than being classified as Diptera in stomach contents, that seems to be about as much as is known. One Dipteran that some skilled fly anglers imitate is the deer fly, Chrysops sp. It would not be much of a stretch to say that anyone who spends any time out-of-doors in Michigan is familiar with one or more of the many species of this pesky fly. While the males are innocuous, the females require a blood meal before laying their eggs, and their bite can be rather painful. Deer flies have one pair of wings, marked with brown spots. Their large eyes are prominent and often have a horizontal stripe or fluorescent appearance. Two somewhat-long antennas extend from between the eyes. The thorax and abdomen can be striped, sometimes horizontally, sometimes vertically, and sometimes a combination of both, depending on the species. Deer flies are active throughout most of the Michigan summer, laying their eggs on vegetation or other solid substrate that extends over the water. Eggs, most often laid in a single layer but sometimes in tiers in a compact mass, are white to light tan when first laid, darkening to deep brown to jet black after a short time. The grub-like larvae drop into the water after hatching, where they will develop in about one year. Pupation takes place out of water and hatching adults will mate soon after. However… there is a deer fly ‘look-a-like’ on the river during June and July that might be the real prey item of trout, possibly overlooked and misidentified over the years. The water snipe fly, Atherix lantha, looks quite similar to the deer fly, with large, prominent eyes, mottled brown wings, and striped abdomens. They lack the long antennas that deer flies possess and fortunately do not bite. They typically swarm mid-day, attracted to anything dark. Individuals can also be found resting on stream-side vegetation. Their life cycle is rather interesting (from a biologist’s view, at least), although some readers may find the following to be a bit on the gross spectrum. After females have mated, likely on stream-side brush, they seek out suitable sites for egg-laying. The flies must oviposit on a substrate that is suspended over water, such as an overhanging tree. However, they quite often lay eggs on the undersides of low concrete bridges, specifically on the outer edges. An individual
water snipe fly will land on a sheltered spot under the bridge, often in a crack or drip hole. Then, additional females are attracted, possibly by pheromones, and will cluster around her, interlocking to one another and the substrate with tiny Velcro-like hairs found on the cushiony pads of their feet. The size of the cluster is variable, often containing a few hundred females to upwards of tens of thousands of flies. The cluster may initially resemble a swallow’s nest or a bee swarm to the casual observer, but a closer look reveals a crusty, caked mass of flies (shown in the photo above, with an insert of a single snipe fly). Some observers report a characteristic odor as well. Each female will lay an average of 450 white, sticky eggs that turn gray after a few days. As the eggs develop, the adult females remain stuck to one another, dying in the cluster. Eggs will hatch within a week and the larvae will crawl around the dead mass of flies. Within hours, the larvae drop into the water where they will grow and develop over the course of one to two years (development is shorter in warmer streams and rivers, longer in colder waters). Water snipe larvae are predatory, piercing and sucking out the insides of their prey. Larvae resemble grubs with a forked ‘tail’ (actually tiny pseudopods) and are tannish with darker brown stripes. They grow to about 10 mm (0.4 inches), feeding on other aquatic insects, including mayflies, caddisflies, and scuds. There is an account of a water snipe fly (Atherix pachypus) that was eaten by indigenous people in California. In certain locales, especially in canyons, the flies were very prolific. An account relayed from the late 1800s described the Klamath Indians being completely covered with the flies in early summer. Harvesting was systematic. Logs were placed in the river so that floating flies would lodge against them. The Klamath would then go upstream and shake the boughs of willow trees which were covered by flies, sometimes 5-6 inches deep. The flies would fall into the river in masses, collecting along the logs placed downstream. Collection took place in the morning when cool temperatures hindered flight. Special baskets were used to gather the flies, upwards of 100 bushels a day, after which they were transported to stone-lined oven pits. There the flies were baked and steamed. After the fire burned out, the product (“Koo-chah-bie”) was cooled and sliced for consumption. So the mystery remains, which fly is the trout eating? Do the adults of either insect fall into the water somehow? Will the real Dipteran please step forward? Some stomach pumping in June and July might provide some answers for this Michigan angler. Meanwhile, try fishing Jerry Regan’s Deer Fly or Rusty Gate’s Secret Rubber Bug. Both are great imitations of the deer fly. And the water snipe fly.
Ann Miller is the author of Hatch Guide for Midwest Streams (Frank Amato Publications, 2011; ISBN -13: 978-1-57188-481-7; $29.95). She is republishing the book in 2021.
