Note: This information is as region specific (S.E. MN) as I can tailor it to be. It may be relevant to Northern Parts of Iowa and Southwestern Wisconsin. Also, if I forgot something/made a mistake in my information PLEASE post with what needs to be changed. This is for my benifit as well as visitors to W.F.F.

Looking at the 1st nymphal category “The Crawlers” there are five Mayfly species that have direct relevance to myself as well as other S.E. MN anglers. The following is a list in order by approximate hatch dates with condensed versions of relevant information. Thank You for the excellent pictures.  

The Crawlers

Dark Hendrickson (Ephemerella subvaria ) 12-14 Reddish brown to tan.  April-May

Look for nymphs in the gravel and vegetation of slower meandering water. These nymphs tend to swim for a longer time and can be twitched upon retrieval. Hatching begins at 50-55 degrees. Hatches 2 points out the importance of poor weather slowing the duns down and providing for optimum fishing dun patterns. 

Light Hendrickson (Ephemerella invaria) 12-16 Tan with olive and yellow cast. Late May-June

These nymphs tend to prefer medium-fast water and like subvaria the nymphs use the current to choose an optimum emergence site. So they make for good nymph fishing because they are movin’! Hatching occurs in water from 50-60 degrees. Hatches 2 makes a big point of noting the size and color differences by a hook size or more between invaria, rotunda and dorothea. Meaning to me that I should tie these slightly larger because I’m looking specifically at invaria. 

Iron Blue Quill (Paraleptophlebia) 18-20 Dark gray with maroon cast. Late May-June 

My book says that the hook size for a dry is supposed to be 16-18. The nymphs tend to prefer quieter water. The gills are much larger on these nymphs than those of ephemerella.

Sulfur (Ephemerella dorothea) 16-18 Orange to cream. Late May-Early July

So my research in telling me that dorothea has typical ephemerella features and will spend time finding a spot to emerge. The book really makes a big point to note that dorothea differs from invaria by a full hook size and color. 

White-winged Blacks a.k.a. Trico’s (Tricorythodes) 20-24 Charcoal. July-Sept

I fished during trico action so I’ve seen these and they are small. The book and other info is right on for a 20-24 size hook. The nymphs thrive in streams with a p.h. of 7.5 and above. Nymphs live in the silt, sand and gravel in slow to medium current. As well as the aquatic plant life. Hatching between 52-56 degrees. Trico’s also have typically a very long period of emergence spanning over months.


Trying to keep this short but very useful. Hope my goal is accomplished. Also, I picked dun photos because I’m tying Compara-Dun Dries at the moment. Pictures coming soon.

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