Brian Asked
Hey Andy,
Good to see you last week. My question is, have you ever seen Dark Hendricksons on the Rush (WI?)



Hi Brian

The Dark Hendrickson question is a good one. When I learned that water temperature variation is the key to the nymphs surviving, the answer may be somewhat clearer. The science says that Dark Hendrickson (E. subvaria ) struggles to exist in streams where there is rapid change in stream temps. Apparently all it takes is 3 or 4 degrees in water temperature change, over a very short period of time, to kill them off. I know there are none in the Kinni and I can say I have never seen a meaningful hatch of them on the Rush. Something is “not right” for them to exist in these rivers. Maybe it is the storm water run off. More roof tops, black top and impervious surfaces that are running warmed water directly into the river. The Southeast of Minnesota, where there is a sizable hatch, generally does not have as much development around the rivers as the Rush does. It is pure speculation but it is one thing that may play a factor. The photo is from a great resource for bug info.
Great Question!