Mayfly Larva/Nymph

Overview  Mayfly adult

Ephemeroptera

Caddis larva  Stonefly larva

1. "Green Drake"
   (Ephemera guttulata)

2. "March Brown"
   (Stenonema vicarium)

3. "Hendrickson"
   (Ephemerella subvaria)

4. "Light Cahill"
   (Stenonema canadense)

5. "Pale Morning Dun"
   (Ephemerella infrequens)

6. "Blue Winged Olive"
   (Baetis flavistriga)

7. "March Brown"
   (Ephemera simulans)

8. "Great Brown Drake"
   (Hexagenia bilineata)

9. "Great Dark Green Drake"
   (Hexagenia recurvata)

10. "Great Olive Winged Drake"
    (Hexagenia limbata)

11. "Great Summer Drake"
    (Siphlonurus occidentalis)

Mayflies are the principle insect in the sport of fly fishing.  There are over 2000 named species in 200 genera and 19 families.  The immature, larval forms of these prolific insects are of particular importance to fly fishers.

Mayflies, having an incomplete metamorphosis, have larva that emerge directly to a winged form without an intervening pupal stage.  Development of larva ranges from a few weeks to 2 years.  The larva are elongate, cylindrical to flattened forms ranging in length from 3 to 30 mm.  They have well developed eyes and slender antenna.  They usually have 2 or 3 long, visible tails.  Wing pads are present and body sides show filamentous gills.

Mayflies occur in almost all freshwater with adequate dissolved oxygen.  The larva are common benthos of flowing water, ponds, and shallow areas of lakes.  Once larva reach maturity, they transform into "subimagos" (also known as "duns".)  This process of changing from the subaquatic (underwater) larval stage to the terrestrial, winged pre-adult stage, is referred to as a "hatch".  For mayflies, this takes place at the water's surface.  This developmental stage is unique to the mayflies.

It is during this process, as the larva changes into the subimago, when the insect must clear the larval case and ready its wings for flight, that gives the fish a brief chance at an easy meal as the insect sits on the surface.  It is at this time that the fly fisher must ply his knowledge in an effort to "match the hatch."

12. "Early Brown Quill"
    (Leptophlebia nebulosa)

13. "Dark Red Quill"
    (Rhithrogena impersonata)

14. "Tiny Lead Winged Red Quill"
    (Centroptilum rufostrigatum)

15. "Great Leadwing Drake"
    (Isonychia bicolor)

16. "Dark Golden Drake"
    (Potamanthus distinctus)

17. "Tiny White Winged Black Quill"
    (Tricorythodes stygiatus)

18. "Little Speckle Wing Quill"
    (Callibaetis nigritis)

19. "Tiny White Winged Sulphur"
    (Caenis simulans)