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Salmonflies: An etymology lesson

With salmonflies on the cusp of hatching here on the Big Hole, we thought it would be good to review the biology behind these big bugs that bring out anglers in masses.

And, if your wondering, we have seen a few early hatching bugs, and anticipate that we will see them begin their annual hatch in the next 3-4 days. We have observed the nymphs beginning to congregate near the rivers edge, and fish are being caught more and more on rubber legs and pumpkin buggers.

The basics: Salmonflies (scientific name Pteronarcys californica) are a giant stonefly in the Scientific Order: Plecopetera. These bugs can be up to 2.5 inches long. Adult Salmonflies can be identified by the bright orange or red band behind their head, and on their abdomen. Adults and nymphs have two antennae on their heads, with segmented bodies and two tails. The adult stoneflies have two sets of wings (totaling four). When they fly (or attempt to), these four wings form an X-pattern. Their poor flying ability makes them an easy target for hungry trout, as they often fall to the water mid-flight.

Life cycle: There are three stages of the salmonfly lifecycle: egg, nymph, adult. Nymphs will live in the river for 2 – 4 years, and when the conditions become correct, they emerge from the water and enter the adult cycle. Prior to emerging they often congregate near the edges of the water, which is generally an indication of the hatch. As adults, they tend to only live for a few days. When they emerge from the water it is time to reproduce, and then they die. Typically nymphs will emerge from the river when it is in the 55 to 60 degree range. They will crawl onto rocks, bridges or overhanging willows and complete their metamorphosis. Typically the salmonflies mate on the ground or in branches/vegetation. After mating, the males will crawl away and die, sometimes dying in the river. The females will then move towards the water to lay their eggs, and this is most often when you see flying salmonflies. The egg sack, which is dark and pea-sized, is deposited on the water, and the female dies shortly after. Eggs sink to the bottom and hatch, to begin the nymph stage again.

Fly selection: Anglers can use either wet flies, to imitate the nymph stage, or dry flies to imitate the hatched adults. Suggested nymphs are Pats Rubber Leg or Bitch Creek in a #4#8 (to imitate varying developmental stages). Dry fly patterns vary, but we like the Flat Foam Salmonfly in a #4 or #6, Bob’s Salmonfly #4-#8, Cat Puke #4, Orange Chubby #6-#10 or Foam Stimulator in the same sizes.


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