Northern Wisconsin Trout Stream Mayfly Hatch Chart
(for mobile devices)

Common Name Scientific Name / Details Mar Apr May Jun Jul Aug Sep
Blue Wing Olives (BWO)(2) Baetis
size: 6-7 mm (#18)
nymphs 3 tails (middle shorter)
duns 2 tails
--XX XXXX XXXX XXXX     XXXX
Gray Drake (?) Siphloplecton basale
size: 14-16 mm (#8)
nymphs 3 tails / duns 2 tails
  --X X--        
Hendrickson Ephemerella subvaria
size: 10-12 mm (#12)
nymphs 3 tails / duns 3 tails
  --XX XX--        
Sulphurs / PMD Ephemerella invaria / rotunda / excrucians
size: 9-10 mm(#14)
nymphs 3 tails / duns 3 tails
    --XX X---      
Sulphurs /PMD Ephemerella dorothea
size: 6-7 mm (#18)
nymphs 3 tails / duns 3 tails
    --XX XX---      
Gray Drake Siphlonurus alternatus
size 12 -16 mm (#8)
nymphs 3 tails
duns / spinners 2 tails
    --XX XX---      
Little Dark Hendrickson Ephemerella needhami
size: 9-10 mm (#14)
nymphs 3 tails / duns 3 tails
    ---X XX-      
Sulphur Epeorus vitreus
size 9 - 12 mm
nymphs 2 tails / duns 2 tails
    ---X XX-      
March Brown / Gray Fox Maccaffertium vicarium
(formally Stenonema)
size 14-16 mm (#10 2x long)
nymphs 3 tails (clingers)
duns 2 tails (speckled wings)
    ---X XXX-      
Armored Speckled-Wing Baetisca laurentina
size 10-12 mm (#12)
nymphs 3 tails (fat body)
duns 2 tails (chubby mottled wing)
    ---X XXX-      
Light Cahill Stenacron / Maccaffertium
(several species)
size 9-1 mm (#12 2x long)
nymphs 3 tails (clingers)
duns 2 tails (speckled wings)
      XXX-      
Darth Vader Serratella deficiens
size: 4-5 mm (#20)
blackish wings
pale yellow legs
nymphs 3 tails / duns 3 tails
      XXX-      
Brown Drake(1) Ephemera simulans
size 12-15 mm (#10 2x long)
nymphs 3 tails (burrower)
duns 3 tails (brown splotch wing)
      XXX-      
Hex Hatch
Michigan Caddis(1)
Hexagenia limbata
size 16-35 mm (#6)
nymphs 3 tails (burrower)
duns 3 tails
      --XX X---    
Mahogany Dun Isonychia bicolor
size 13-16 mm (#8 2x long)
nymphs 3 tails (swimmers)
duns 2 tails
      ---X XXXX XX--  
Tricos Tricorythodes minutus
3 -3 1/2 mm (#22)
nymphs 3 tails
duns 3 tails (blackish body)
        -XXX    
Large Rusty Spinner(1) Hexagenia atrocaudata
size 16-30 mm (#6)
nymphs 3 tails (burrower)
duns 3 tails
        --XX X---  
Little Yellow Quill Leucrocuta hebe
size 9 - 12 mm
duns 2 tails
duns yellow body & orange thorax
        ---X XXX-  
White Fly(1) Ephoron leukon
size 10 - 13 mm (#12)
nymphs 3 tails (burrowers)
duns 2 tails (white body)
          XXX-  
Common Name Scientific Name / Details Mar Apr May Jun Jul Aug Sep

Notes:
(1) - indicates mayfly nymphs that burrow in sand, silt and muck. The densest hatches for these insects will occur in those stretches of the stream.

(2) - there are several mayflies species that all fall under Blue Wing Olives (BWO) and hatch at different times during the season. Some I see are too sporatic to really get the trout's attention.