AQUATIC INSECTS: TOP TO BOTTOM
by: Bob Shannon
In Vermont, the month of May is typically the start of dry-fly fishing season . As water temperatures rise into the low and mid- fifties as a sustained average, dry fly fishing becomes more the “norm”. One of the first major prolific hatches of the early season would be the mid-day Hendrickson hatch (Mayfly Species Ephemerella subvaria).
The trigger mechanisms for hatch cycles are water temperature, and photo phase (sunlight level). Early season hatches are generally triggered by the warming effect of the water. This can be triggered by temperature fluctuations at various inlet areas of smaller feeder streams, spring pockets and sunlight levels that heat up the water during the warmer days of May. A water temperature variation of just a few degrees can be enough to trigger a hatch cycle. Anglers who gain a basic knowledge and understanding of this magical insect life cycle have a much stronger level of confidence when selecting flies that represent the four stages of the insect life cycle. The stages of the insect life cycle determine the fish feeding patterns.
Let’s take a look at the scientific cycle of aquatic insects to give you a better understanding of how your fishing tactics will work. Healthy Vermont river bottoms are blanketed with three major aquatic insects; May flies (Ephemeroptera, meaning winged and short-lived), Stone flies (Plecoptera, Latin for braided wing), and Caddis flies (Trichoptera) . These three major aquatic insects have 4 fishable stages for the fisherman. The first stage is the nymph-larvae. Nymphs and larvae burrow, cling, or crawl along river bottoms foraging for bio-mass which they will feed on for a 1-3 year cycle. During this cycle, anglers need to focus their attention on fishing the bottom column of water with an indicator system to target fish feeding on the nymph-larvae.
At the end of the first cycle, the nymphs/larvae swim or crawl from the river bottom to become winged insects. The emerging stage of the aquatic insects is known as the wet-fly stage to the fly fisherman. The insects are very vulnerable during this cycle and fish feed heavily in the mid and surface columns during this quick transformation stage. The emergence of the insects is measured in seconds, not minutes. Once the nymph/larvae reach the surface film of the river, it sheds its nymph casing to become a winged insect (dry fly).
Now we are fishing dry flies. The dry fly or dun (as it is scientifically referred to) then travels along the surface column of water struggling and fluttering its wings to eventually fly away as a winged, air breathing insect. The metamorphous or transformation from water-breathing insect to air-breathing insect is quite unique. Fish are now rising to the surface to feed on the dry fly. The final stage, and the last opportunity for fly fisherman to catch trout on the life cycle, is when the insects return again to the river, typically within 1-5 days to lay their eggs and ultimately die on the surface film as a spinner. Then the eggs filter to the bottom, hatching into small nymph/larvae to begin the cycle again.
Most fly anglers prefer the visual excitement of the surface strike so let’s focus on the surface or dry fly. Hendricksons are an example of early season, dark – colored aquatic insects that absorb the heat from fluctuations in water temperature primarily caused by sunlight penetration. Other early season hatches to keep your eye out for would be Quill Gordons (Mayfly Species Epeorus pleuralis), Black Stones (Pteronarcys dorsata), Dark Caddis , Blue Winged Olives (BWO- Mayfly Genus Baetis). Most early season dry-fly fisherman should try to time their peek opportunities between 2-6 p.m.
Those unfortunate folks who work 9-5 jobs will find these time periods to be a challenge. As a seasoned fly fishing guide, my recommendation is to always be prepared for a mid-afternoon business appointment that requires a 4-piece pack rod that can be conveniently concealed in one’s briefcase. This affords them the opportunity to sneak out of the office for a mid-day appointment with Dr. Hendrickson. For those who can’t conceal their fishing pack rod past the watchful eye of their shift manager, an early evening spinner fall will give you the opportunity for some late afternoon dry-fly fishing. Keep in mind that the surface action is generally slower in the evening than during the mid-day peak hatch periods. Early season dry-fly fisherman will find the opportunities for taking trout to be much easier than the later part of the dry-fly season in the fall. This is due in part to the trout’s eagerness to feed on surface patterns at the beginning of the season.
Early dry-fly fishing is very productive due in part to the large sizes of the early season hatch. Hook sizes range from size 10-14, making it easy for the trout to see, and more importantly making it easy for the fisherman to see as well. Early season hatch cycles typically run a solid two to three weeks. Trout will become programmed to the consistent daily pattern of these early season hatch cycles, making dry-fly action consistently productive throughout the month of May.
The term “May fly” may imply that May fly hatches are limited to the month of May. However, May flies, Stone flies, and Caddis flies will hatch throughout the remainder of the trout season. Those looking to sharpen their skills in aquatic insect identification to better “match the hatch”, will want to use the New England Trout Stream……. guide to their advantage.
Remember, to maximize your dry-fly opportunity, you need to target surface feeding fish during surface feeding cycles. As water temperatures rise in the months of June, July and August, feeding patterns will switch from mid-day cycles to sunrise and sunset cycles. Being on the water at the right time will be the key to your dry-fly success.