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All about Caddisflies

What Do You Know About Caddisflies?



What is it about caddisflies that is sometimes so unpleasant for anglers? No one will argue that these flies are important to the trout, thus making them important to the angler, but they are surely a fly that most anglers would rather not think about. Part of the reason might be because they are so darn frustrating to match in pattern and behavior.


I think this is fascinating, from Gary Borger's book Caddisflies. Borger states that there are three areas in which caddisflies concentrate during a hatch:


1. The emerging insects, fully formed adults inside thin and flexible pupal skins, cut their way free of the cocoon. Most species do not begin to rise immediately, though. Before they can start swimming they must generate air bubbles inside the transparent pupal skin. They drift momentarily with the bottom currents, enough of them carried along to create a concentration of helpless prey...Trout can feed for hours on these forms without breaking the surface or chasing an active insect.

2. Ken Thompson, an aquatic biologist, put the role of the surface film during emergence into perspective, “The meniscus, or surface film, poses an unbelievable barrier to insects trying to pass through it, either from above or from below.....A great amount of physical energy is required for an insect to break through the ...meniscus. An example, in human terms, would be the amount of energy needed for a full-grown person to escape if he were covered with three feet of dirt. Aquatic insects have evolved (through necessity) various ways to overcome this barrier. Swimming emergents swim to the surface and push against it. When the top part of the pupal thorax protrudes through the surface and splits open, a meniscus forms around it, thus creating an escape hole in the surface. As the pupal skin (nymphal skin in mayflies and stoneflies) splits open, it is actually aided by the force of the surrounding meniscus, and the adult insect passes through the hole, never touching the water.... This is the stage that triggers the visible feeding.

The peak feeding, with fish rolling and jumping all over the stream, should be a time when fly fishermen master the fish, but it can be a time of total failure and frustration. Too often anglers fail to realize that the insects are hesitating and concentrating under the film, not on it, and as a result they mistakenly assume that it is an occasion for dry flies.

3. Cripples are usually not important during the main hatch because they are not concentrated. During a heavy hatch, over a prolonged period of time, there are nevertheless quite a few of them, and if they could be gathered into a small area they would become a significant food source. Fortunately, for both trout and trout fishermen, that is exactly what happens after the hatch. Even after they drown, these crippled insects remain quite buoyant and are swept along with the current. Eventually many of them join with bits of flotsam or foam and collect in a backwater of the stream to become a great, swirling cafeteria for the fish...It is after the main hatch that the leftover cripples become the center of attention.

· On some trout streams Caddisflies can constitute as much as 45% of the total diet for a 10-15” trout.

· A trout in a stream can gain as much as 50% of its yearly growth during 2 months of spring or early summer.


Borger's book is fascinating and there is so much more to learn than what I've quoted here. Find a copy if you can. I pulled this from the first 20 pages and there are over 300 pages in the book!



Here's a short clip from Tom Rosenbauer about Caddisflies.






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Caddis Pupae Give-Away



The air bubbles that Borger describes above are what fly tiers strive to imitate with translucent materials such as the poly fluff that we are using on some of our fly patterns in the store. It’s an amazing material in that it gives the illusion of bubbles on pupae, it sparkles and helps capture the light on mayfly spinners and is perfect for the March Brown and Slate Drake cripples because it provides an excellent imitation for a clump of deformed or crippled wings.


All you have to do to be in the drawing for a baker’s dozen of our caddis pupae (or emergers) is send us a comment of Caddis Give Away and we’ll put all the names into a hat a draw a winner. We’ll announce it next week.



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