Saturday, January 22, 2011
Wierd Looking Mayflies: "Common Burrowers" and "Armored Mayflies"
There are a couple of mayflies that are hardly ever seen in our watershed. In fact this one -- the "Common Burrower" (family: Ephemeridae) was seen for the first time last year. And, it was found in two very unlikely places -- the upper reaches of the Doyles River, and the Albemarle County reference site, both clean, cold, rocky upland streams with very little silt and sand. That is not the habitat this insect prefers. It does like cold water; but it inhabits slow-moving pools, normally in larger rivers.
The burrower nymphs use their tusks and robust front legs to dig out "U" shaped tunnels in gravel and sand. There they stay during the day, emerging at night to forage. From the two-pointed projection in front of its head, we know that the genus of this particular nymph is Ephemera: whether it's E. guttalata (the "Green Drake") or E. varia (the "Yellow Drake"), I'm not really sure. But from pictures I've seen, and the shape of the tusks, I'd go with the latter.
The "Common Burrower" genus and species preferred by fly fisherman -- especially those who live in New England and the upper Midwest -- is Hexagenia limbata. This hatches into one of the largest mayflies we see in the East, one sometimes mistakenly called the "Michigan caddis." When I lived in Vermont, we simply called it the "Hex" hatch. This is a large yellow mayfly that when it pops to the surface looks like a small sailboat, and the Trout simply go nuts. Unfortunately, they tend to hatch right at dark, so you're not always sure where to cast.
There is another burrower that I take it is found in the East -- but I've never seen it. This the "Hacklegill mayfly" (family: Potamanthidae) -- pictured in the photo above. For fly fisherman, it's the "Golden Drake". This would be found in the warm, silty waters at the edges of rivers -- places where stream monitoring groups rarely sample. But it would be worth checking the Rivanna, or even the James, sometime to see if they're there. The nymph in the photo above travelled back to Virginia from the Clark Fork River near Missoula, Montana, safely stored in my luggage after my annual fishing trip.
Finally, the other "wierd" mayfly that is seen only rarely in our watershed streams is the "Armored mayfly" (family: Baetiscidae). StreamWatch occasionally finds them in its reference streams, and I believe one was found last year in Preddy Creek near Ruckersville. It's one strange looking critter!
(And it's of no interest to fly fishermen whatsoever.) It's distinguishing feature is the large carapace that completely covers the thorax and most of the abdominal segments, and thus all of the gills.