Caddis Entomology

Brachycentridae Larva/Case

For me the difficult part about Caddisflies as they relate to trout is determining what is going on. Seems kind of “duh” but it breaks down something like this. On stream, splashy rise, see a few adult caddis fluttering around, maybe catch one match the size/shape/color as best I can but that’s when things fall apart. Sure I can throw on any number of adult dries that might meet most requirements but the complexity of the Caddis makes further choices difficult. When that adult pattern doesn’t produce a rise no matter how it is presented something else must be determined. Which specie? What does the larva look like? What kind of pupa should I try? Perhaps that splashy rise came as a result of a pupating caddis attempting to make a break for freedom and not the adult I see fluttering around. My goal here is to not become an expert on Caddisflies (I’m not going scuba diving in my favorite hole like La Fontaine) but rather to be able to make a few [singlepic id=2080 w=320 h=240 float=right]educated guesses. So where to begin? Well I know where, it’s sitting at home on a shelf next to some of my favorite texts and you can view it here. I am fortunate to have a bound copy and glad to own it.

The Guide to Aquatic Invertebrates of the Upper Midwest. You know your a bug nerd when you are excited to have this on your bookshelf, that or your in classes at the U of M to become an entomologist. So you get your hands on a copy of this beast. Now you have to decipher it, this can be challenging. Any number of terms that I have to look at twice just to pronounce make all the difference in the world of the caddis fly, especially when it comes to identifying the larval specimens. The U of M and a few other Universities have good aquatic insect identification tools. I point to the U of M’s Aquatic Insect Interactive Verification Program because it is meant to work in tandem with the guide book listed above. A second online identification resource comes from North Dakota with great images and explanations of all the complex terms that make up invertebrate identification. Collecting a [singlepic id=2079 w=320 h=240 float=left]few specimens, toting them home then using the verification program will help narrow the field with which I can look to the guide for further specific identification.

Out in the feild it becomes quickly apparent that the ratio of Caddisfly larva to say Mayfly larva is drastically skewed towards the Caddis just flip over a rock or shake a few weeds. Combine that information with the fact that fisheries biologists working for the DNR in our region can point to scientific research stating that the spring fed creeks we have here are so packed with trout food of all kinds that the need to feed on drifting insects diminishes with the age/size of an adult Brown trout. That is not to say they don’t feed on drifting invertebrates but rather they have a choice and the larger fish may be choosing to pick those millions of rocks packed with millions of cased caddisfly larva as an easier meal than waiting for the occasional drifting food item. That thought has me concentrating on the caddisfly larva, attempting to imitate the larval forms and use the indentification guide to hopefully gain a better grasp of which larval forms will transition to which pupal and adult forms.

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