I Plauditus punctiventris: the Mayfly Formerly Known As Pseudocloeon

OK, you say, but what happened to the name "anoka?" Well, researchers also regarded Pseudocloeon anoka, described in 1945, as having been described earlier (1923) as Pseudocloeon punctiventris, and they eliminated the name "anoka." So, Pseudocloeon anoka is now Plauditus punctiventris. The now-discarded species name "anoka" came from the town in Minnesota where the species was collected, while the name "punctiventris" refers to a row of dark dots or "punctures" on the ventral side of the male spinner's abdomen. Whatever the name, we're looking at a dun or spinner tha only measures 4-5 mm long. The front wings appear quite broad, while the hind wings are absent. The color of the female duns I have examined locally is a light-green or yellow-green; I'd call it more green than olive. The green color is also stronger in freshly emerged duns than in specimens several hours old--beware if you net and bring specimens home to match dubbing colors. The males I netted were less intensely green and more pale olive or tan than the females.

The nymphs can be very common on rocks in riffles and they also clamber about on vegetation in more quiet waters. They have the typical swimming-type shape as do their very similar cousins in the genus Baetis. They swim rapidly with up-and-down movements of their abdomen. They are most easily distinguished from nymphs of Baetis by the presence of only two tails and no hind wing pads. In the nymphs I find in the Rush River, the cross-bar or band at the middle of each of the two tails, plus faint spots on the ventral side of the abdomen, identify the species as P. punctiventris.

By Dean Hansen

Movie actresses, entertainers and rock stars change their given names with abandon. Norma Jean Baker became Marilyn Monroe and Prince becomes The Artist. Insects aren't quite so vain or particular, yet their names also are changed, far too often. Such is the case of a common Midwestern mayfly formerly known as Pseudocloeon anoka, the Tiny Blue-winged Olive. A couple years ago, its name was changed to Baetis punctiventris, but it's now officially known as Plauditus punctiventris. "P. anoka" had been known to both entomologists and fly anglers for half a century, although I'm sure the species was noticed by many anglers long before that. And well it should have been noticed--the larvae can be extremely abundant and the species' prolific hatches on cold, limestone streams can produce some of the best surface feeding activity of the season.

What the species has going against it, however, at least as far as fly fishers are concerned, is size: It's tiny. An adult easily perches on a pencil eraser with room to spare all around. With a body length of about 4 mm, Plauditus punctiventris demands an imitation in the #22 to #26 range and a 7X tippet to boot. A male spinner, in fact, makes even a Trico look big.

This summer I waded into a riffle of the Rush River in west central Wisconsin and captured the flying duns in my aerial net. I was awed by the number of gentle sipping rises in the pool just upstream. There were no fish leaping out of the water or even showin their fins or tails--it was just sip, sip, sip, sip. There must have been a couple dozen brown trout feeding on emergers or floating duns in that small pool. While I was loaded with camera and collecting gear and didn't fish that overcast afternoon, several Saturday morning coffee drinkers at our local fly shop describe outstanding dry-fly fishing to "Pseudocloeon" hatches in June and July, and again in September.

So here we have a mayfly species present in sometimes incredible numbers which, with the right imitations and presentation, can almost be given "superhatch" status. Just what is this "formerly known as Pseudocloeon" mayfly, anyway? The genus Pseudocloeon was described in 1905 for a species from Java.

The genus came to be distinguished from other Baetis-type relatives by the lack of hind wings and, as species were discovered in North America, by the presence of two tails in the nymphal stage. It seemed easy and straight-forward: two tails as nymphs, no hind wings as adults and we have Pseudocloeon. But closer examination of many species in the large Baetis-Pseudocloeon group led mayfly researchers recently to remove North American species from Pseudocloeon and place them in Baetis, Acentrella, or Barbaetis. This change was reflected in Knopp and Cormier's recent book Mayflies, where punctiventris was included in Baetis. Then less than a year ago, two mayfly researchers created the new genus Plauditus, and they transferred punctiventrus from Baetis to the new Plauditus. Talk about genus-hopping--three names in as many years.

To the top of the next column

 But looking for the absence of hind wingpads in the nymph or hind wings in the adult requires a 15X microscope, and streamside identification to species level doesn't seem that critical. Look carefully at the surface of rocks in a riffle areas for small (4mm, or 3/16" long) nymphs and, if present, try dead-drifting a #20-#24 olive nymph pattern. If you see tiny duns in the air (also look for cedar waxwings flying out from the streamside alders to take airborne duns), try either a #22-#26 olive emerger or an olive Compara-dun, parachute or no-hackle dun imitation.
Emergence can be slow and steady from late morning to late afternoon on overcast days, but warm sunny weather produces a more intense emergence closer to evening. Fish each tiny riseform as if there is a large trout under it; occasionally there will be. Spinner falls occur towards dusk, and fishing them requires a Compara-spinner or spent-wing pattern, again in that challenging tiny #22-#26 range.

Pseudocloeon or Plauditus, anoka or punctiventris--whatever you want to call it, it's a mayfly well worth learning. It can present some challenging hours both at the fly tying bench and on the stream, but, given its abundance and extended emergence time, its importance to the Midwest fly angler is way out of proportion to its tiny size. You'll do well not to ignore or dismiss this species.

Dean Hansen has a PhD in aquatic entomology and teaches classes in trout stream ecology. His column appears in every issue of Midwest Fly Fishing: Don't miss it.

copyright Midwest Fly Fishing Magazine 1999