Fly Hatches on Falling Spring 
by
Eugene P. Macri Jr.
Aquatic and Environmental Scientist

Fly hatches on Falling Spring (Falling Spring Run) are different than most freestone streams. Because Falling Spring Run is a limestone spring creek the diversity of the hatches will be limited by the extremely coldwater conditions found there. Furthermore, smaller streams have less diverse substrates and current speeds and this also limits the diversity of the invertebrate population in the stream.

Fly hatches on spring creeks tend to have longer durations than on freestone streams because usually the insects build up larger populations in the invertebrate community compared to freestone populations of the same species.  Furthermore, the hatches may be spread out more during the season and on some streams the hatches will be more intense.

Let's start with the mayflies (Ephemeroptera) and discuss one of the more important hatches on Falling Springs.

The Blue Winged Olives
Part 1

The Blue Winged Olives are an important group of mayflies on Falling Spring.  Most of the Blue Winged Olives are Baetis tricaudatus Dodds if you are interested in the species. I should know because I've done all the research on these spring creeks.

This mayfly will be from sizes 14-22 on the stream.  The early season varieties will surprise you with their size.  As the season progresses the mayflies get smaller.  The Blue Winged Olives have a number of different broods per year on the stream.  They tend to come off in cloudy, and some times nasty weather.  They are often hard to see because of the back ground of the sky without a lot of contrast.

They also are substrate and current specific so they may emerge on one section of a riffle and not another. They do not come off in a blizzard. They usually emerge off and on throughout a time period and through out the year.