The Stream Doctor

January 6th, 2003

Your questions and answers about everything stream related.

Q. From Dan in N.J.... Last August I saw a Mayfly that had landed on my house. (I live in N.J.) The mayfly was all white and looked similar in size and coloration to Ephoron leukon. (I had seen a picture in a fly fishing book.) There are no streams of any size near my home but I do live about a half mile away from an eleven acre pond and about 3/4 of a mile from a 300+ acre lake. A very small (you could jump over it) brook drains a swampy area into the pond, which is then drained into the lake. The swampy area get very dry in the summer and the "brook" is barely a trickle at that time of the year. Do you think that the mayfly came from the lake or pond, or from the little feeder brook? The brook flows through a wooded area and is densely shaded as soon as the leaves come in, so the water remains fairly cool. Also, how far do mayflies and other adult aquatic insects stray from a stream after they have mated and are basically waiting to die?

A. If the mayflies were Ephoron leukon, then I suspect they came from the lake or pond. E. leukon inhabits relatively large streams or in gravel and sand shoals in lakes; thus it is more likely they came from the lake or pond than the small brook. Adult aquatic insects have been known to fly considerable distances after emerging; we have records of hydropsychid caddisflies flying about 10 miles upstream in the Columbia River. They probably don't fly as far laterally from a stream, but have been found up to a mile away. Realize that the wind can carry them, so all of the distance may not include active flying. The long upstream migrations are related to the tendency of females to fly upstream prior to depositing their eggs. Once they have done this, or the males have completed copulating, they don't move very far.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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