Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin

Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Here Oksrukuyik Creek flows away from the Dalton Highway toward the pipeline. It eventually grows into one of the major rivers of the North Slope, and the main drainage to the west of the Sag, but where it crosses the road it's just a small grayling stream.

From Oksrukuyik Creek in Alaska

Stream photos

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Male Callibaetis ferrugineus (Speckled Dun) Mayfly Spinner Male Callibaetis ferrugineus (Speckled Dun) Mayfly Spinner

Lateral view of a Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho

This is one of four specimens I photographed together from the same hatch, also including a nymph, a male dun, and a female dun. According to the key in Check (1982), the clear wing venation on the associated dun shows that it is either Callibaetis ferrugineous or Callibaetis pallidus, and the characteristics to tell the difference between those two are maddening for both the nymph and adult. If the partial shading in the wing is "medium to dark brown," and the dots on the body are "fuscous to dark brown," then it's ferrugineous. If the wing shading is "chestnut brown" and dots on the body are "yellowish to chestnut brown," then it's pallidus. However, several spare specimens I collected alongside the one in the photo have no markings on the wing at all, which would seemingly indicate ferrugineous according to the key. It's enough for a contingent ID, but I still wouldn't rule out pallidus.

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27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.

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True Fly Family Tipulidae (Crane Flies)

Tipulidae (Crane Fly) True Fly Adult from Brodhead Creek in Pennsylvania

Craneflies are only occasionally important. There are rumors of fishable mating flights, but most anglers will not encounter them. The larvae are probably the most important stage in the trout's diet.

Hatching behavior

Craneflies pupate for one to three weeks. The species which do so in the water then swim to the surface to emerge in the style of caddisflies, and are presumably vulnerable to trout, though I have not read about good fishing during these events.

Swisher and Richards in Selective Trout say the larvae all crawl out of the water to pupate, conflicting with the above account. There are so many species that it seems likely both behaviors occur in some species.

Egg-Laying behavior

Adult craneflies are occasionally important during their mating flights when their clumsy flying can crash them by accident into the water. Windy days may also blow them in.

Larva & pupa biology

Diet: Mostly vegetation

Many cranefly species live in many different underwater habitats, and others live in moist soil nowhere near the dirt. We anglers are only concerned with the former.

They live as larvae for about a year and sometimes the larvae end up in the drift in good enough numbers to get the trout excited. Buggy grub-like flies are locally known to perform well on certain rivers, and this may be due to a good population of drifting cranefly larvae (or perhaps I speculate too far). In general, larvae are more likely to be important than the adults.

Ernest Schwiebert notes in Matching the Hatch that they are most common in trout stomachs after the water has been high.