This is an article I wrote for the 2015 winter issue of Fly Fusion magazine. Fly Fusion is probably the most informative and artistic fly fishing magazine in print. I have not written for them lately but I do still have a paid subscription - something I would suggest to anyone with an interest in fly fishing.
There are defining moments in every aquatic insect’s life-cycle when they are at their most vulnerable; nymphs caught in the drift and tumbling with the current, pupa rising to the surface to emerge, emergers in the surface film struggling to get free of their shuck, crippled adults that have failed to get free of their shuck, and fully emerged adults floating helplessly as they wait for their wings to dry so they can take flight. Both trout and fly angler alike are well aware of these key moments and are quick to capitalize on them. But there are other vulnerable stages in some aquatic insect life-cycles that many anglers are unaware of. If you know what to look for, these stages can provide additional opportunities for some exciting action by extending the hatch into extra innings.
One such stage for some aquatic insects is the act of oviposition (the process of laying eggs), or more specifically their behavior surrounding oviposition. Many adult aquatic insects lay their eggs using a rather haphazard approach, fluttering on or over the water and randomly dropping eggs individually or in clusters. The eggs settle to the bottom, or get trapped among aquatic vegetation, where they may reside for a few hours to a few weeks before hatching. Other aquatic insects have evolved egg laying strategies that take a more controlled approach, where eggs are carefully placed in locations that are relatively safe from hungry scavengers and where environmental conditions are most likely to result in successful development and hatching. Some of these strategies can involve laying eggs on overhanging vegetation – as the eggs hatch the juveniles simply drop into the water (a few species of caddisflies are known to do this), while others have adults hiding eggs in rotten logs using a modified ovipositor designed for drilling (this one is common in dragonflies). But many of these behaviors do not result in significant exposure to feeding trout. The egg laying behaviors that are of greatest interest to trout are those found in insect species where the adults physically crawl under water to deposit their eggs.
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| Blobs of caddisfly eggs (Nemotaulius sp.) laid on a willow branch overhanging the water along a wetland. |
Underwater oviposition is known to occur in at least 50 species of Baetis mayflies (blue winged olives), along with over 100 species of caddisflies in the groups Brachycentridae (Grannoms), Hydropsychidae (Spotted Sedges), Rhyacophila (Green Sedges), and Glossosoma (Turtle-case makers). This behavior can also be seen in a few other groups including some species of damselflies, but the best fly fishing opportunities are generated by the afore mentioned groups found in rivers and streams.
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| An adult Caddisfly (Brachycentrus sp.) making its way under water to lay eggs. |
This unique egg laying behavior presents the adults to feeding trout in ways not often considered by most fly anglers. Shortly after mating, adult females return to the stream and seek out riffles and runs with larger rocks or logs that are partly protruding from the water. As they climb down the side of the object and enter the water air is trapped on or under their wings. This air bubble will sustain them while they crawl to the underside of the object to deposit their eggs. Once a suitable location is found, eggs are laid in small clusters. Oviposition can take just a few minutes, or the adult may be submerged for an hour or more. When egg laying is complete the adults will either swim back to the surface and fly to nearby vegetation, or simply release their hold and drift with the current. It is these swimming or drifting adults that trout will often selectively feed on in the days following a hatch.
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| An adult Baetis mayfly spinner penetrating the surface film as it makes its way under water to lay eggs. |
Since much of the activity takes place below the surface this extension of the hatch often goes unnoticed. As usual, careful observation is required to determine when this opportunity presents itself. It helps to know what has been hatching (or was expected to hatch) in the day or two preceding your time on the water. If hatches included groups that are known for underwater oviposition, look on the undersides of rocks or logs to see if any egg masses are present (be sure to carefully replace objects exactly as you found them so the eggs can complete their development). Egg masses will be seen as either thin opaque sheets (usually Baetis), or small gelatinous masses (most common in caddisflies). Of course the presence of eggs alone will not be enough to tell you that egg laying is actively in progress – also look for adults entering the water, or clinging to the underside of those same objects. Most egg laying activity will take place in the morning hours although some species will lay eggs at any time throughout the day. Baetis will typically return to the water to lay eggs in the mid- to late afternoon on the day following the hatch. Active egg laying means that submerged adults will be present in the drift.
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| An adult Baetis mayfly spinner in the act of laying eggs on the underside of a log. |
Matching submerged adults drifting in the current can be a simple matter of selecting a wet fly pattern in the appropriate size and color. March Brown, Hare’s Ear, and Blue Quill wet flies in various sizes will cover just about any situation you may encounter. While these traditional wet fly patterns will certainly catch fish there are some modifications that will improve upon the fly’s ability to elicit takes. For larger caddisflies, wet fly patterns tied with more realistic mottled turkey feather wings tied tent style seem to get a little more attention (one could even trim most of the hackle off a Quill-wing Caddis dry fly and fish it wet). The addition of a few strands of silver Flashabou tied over the wings and a rib of fine silver wire will add that sparkle that the trapped air in the natural creates. For smaller caddisfly and Baetis patterns (#16-20) replace the wings entirely with two strands of fine silver tinsel. Because these flies are fished subsurface, matching the body color of the natural becomes more important than when fishing dry flies, where the fly is seen by trout as more of a silhouette. This is an especially important consideration in Baetis where the color of the spinner will be different than the blue winged olive color of the dun (Baetis spinner body colors are usually rusty-reddish-brown or bluish-gray). In all cases it is important to keep the size of the fly consistent with the size of the naturals – many anglers are reluctant to fish the smaller Baetis and caddis patterns, thinking them too small to be noticed by larger trout, but all trout have excellent vision and they will pick out tiny flies in the drift even in somewhat murky conditions.
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| With egg laying complete, this Baetis mayfly spinner is destined to become a part of the drift. |
In fact many fly anglers are often reluctant to fish wet flies in general, thinking of them as old school, or no longer relevant in today’s world of modern fly gear and advanced fly tying techniques. We may have advanced in terms of high-tech gear and modern materials but fly anglers in the early half of the last century were well aware of underwater oviposition and did not hesitate to develop flies and tactics to imitate this behavior. These flies and techniques have for the most part fallen by the wayside in recent years, and for those who shun them, they are missing out on some spectacular fishing.
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| A selection of size 16 and 18 wet flies to imitate tiny Baetis spinners in the drift. |
Most of the time you will be fishing these patterns on a dead drift using standard nymphing techniques but there are a couple of special situations to watch for. Trout feeding on submerged adults will sometimes move into surprisingly shallow water; often lying in the skinny edge-water of a run, or nosing right up onto a riffle to feed. Here, shallow water nymphing with a tiny yarn indicator a few feet up the leader can be a very effective method. This situation is quite common on the Bow River and other tail water fisheries the day after a Baetis hatch. Also, if you notice that submerged caddisflies are not just drifting, but are actively swimming back to the surface, position your cast so that the tail end of you drift ends up in the seam or slightly deeper water where the fish are holding. Dead drift the fly off the riffle and then stop the drift and allow the fly to ride the current to the surface. Takes on the rising fly are often very aggressive so you want to avoid pointing your rod directly at the fly – keeping the rod at a slight angle will absorb the impact of the take.
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| The day after a Baetis hatch - hundreds of egg patches on the underside of a small, single piece of in-stream wood, a testament to the numbers of Baetis spinners in the drift on the day following a hatch. |
Like a hatch, underwater egg laying events draw the attention of feeding trout by virtue of the number of bugs in the drift. The day or two following a hatch may see thousands of adults crawling underwater to deposit their eggs. The reliable Baetis hatches we have grown to anticipate, that never seem to result in fishable spinner falls, do produce spent spinners. It’s just that the spent spinners are drifting subsurface, wings swept back and looking more like wet flies. Caddisflies also return to the river en masse to complete their life cycle, quickly skittering underwater and laying eggs, before making the trip back to the terrestrial realm – a journey that is often interrupted by hungry trout. These feeding frenzies can produce some fantastic fishing at a time when hatches may be absent and most anglers are plying the water with searching patterns. For the observant fly angler this is all a virtually untapped resource. It’s almost like fishing a new and unknown hatch all-together. Consider it a hatch that has gone into overtime.
