Michigan Flies

Hatches / mayfly

Bat Fly

A

Baetisca spp.

Also called Armored Mayfly, Baetisca, Humpback Mayfly.

An oddball June mayfly with an armored, humpbacked nymph and an extremely fat-bodied adult. Nymphs crawl out to emerge in late morning or midday, so the dun is rarely on the water; the fishable events are the crawling nymph near shore and the spinner fall at 8-9 pm. Standard slim spinner patterns fail because the natural is so stout; tie or buy a #16-18 spinner with a fat dubbed body. A minor hatch, but worth recognizing when trout refuse ordinary June patterns.

#16–18morningmiddayeveningnymphspinnerdark brown to reddish-brown body, very stoutgray wingarmored humpbacked nymph

© harrier · CC BY · iNaturalist · Lake Toxaway, NC · 2025

Timing by region

  1. Southeast Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    May 18 – Jun 16
    Peak
    —
  2. Southwest Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    May 22 – Jun 20
    Peak
    —
  3. Northeast Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    Jun 1 – Jun 30
    Peak
    —
  4. Northwest Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    Jun 1 – Jun 30
    Peak
    —
  5. Upper Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    Jun 22 – Jul 21
    Peak
    —

Flies that match

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