The study of insects is an interesting pursuit in and of itself. For fly fishers, it enhances catchinganother good thing, in and of itselfand deepens the enjoyment of the entire experience. As you get to know the aquatic insects of trout water, you may come to find them to be as fascinating as the fish. All of nature's works are beautiful in the way they shape and are shaped by all other things.
We all seem to aquire a revulsion to bugs, spiders, and all those hairy, leggy, scurrying, biting, disease carrying things. If you can overcome your squeamishness, and handle a few trout-water insects, you'll discover they are harmless and interesting. They don't bite, sting, or ooze green juice. The dobson fly larva, called a hellgrammite, can give you quite a pinch, and there is a water beetle that can poke you with its proboscis, but that's about it. There is nothing in the league of a black widow spider to fear harm from. If "bugs" give you the heebie-jeebies, go with a brave friend. Knowledge will vanquish your fear.
There are aquatic insects which anchor to one spot, and those which crawl the bottom or vegetation, some which excavate burrows, and others which swim. Many species perform behavioral drift. When ready to become adults, some of these bugs swim from the bottom to the water's surface, others crawl out onto protruding rocks, sticks, etc. Having left the water and mated, the females will return to deposit fertile eggs. Some drop their eggs at the surface, others make their way to the bottom or to submerged vegetation. Soon, like the males, many will fall exhaused back into the water, where once again they become food for trout.
Another category of insects that are eaten by fish is hapless terrestrial insects, e.g. grasshoppers, ants, beetles. Their presence is accidental, their predicament fatal. Fish eat them when they happen by. Fish their imitations when nothing much is happening. In high elevation lakes, fish them as your first choice they comprise the main component of the fish diet. more info
You might want to collect insects which are floating by you in the stream, or flying about, or in the stream bed. You can buy or easily make what you need to do this.
An aquarium net works great for collecting from the water's surface. Get one at any aquarium supply store. These nets are easy to carry with you on stream. Mine has a vinyl-coated wire frame and handle. I bent the handle into a crook. The net slips inside the top of the waders with the crook hooked over the wader's top edge. That keeps the net from falling down to my belt. (If it does fall down there, retrieval isn't difficult.)
You can create a comical reputaion for yourself, hopping around waving your hat in the air, but it's a fair technique for capturing flying specimens. A fine-mesh bag, sewn to slip over your landing net would be an improvement. Get the netting at any fabric store. Sew it to have a deep belly. Folded, it fits easily in your vest. (Works fair for seining the stream, too.) A long-handled insect collection net would be the best, but carrying it while fishing might be a problem.
To do a good job sampling the insects in the stream bed, use a simple-to-build seine. You'll need two rods, some fine mesh, and ten minutes.
Depending on how specific you need to get, your viewing apparatus can be one good human eyeball (corrective lenses, if appropriate) or a 10X loupe. You can get a loupe at a photo supply shop. Especially for tiny critters kicked up from the stream bottom, a white dish makes examining the specimens easier. I use the lid of a plastic tub of yogurt. It's free, it doesn't break, it doesn't poke me, it's free.
A set of tweezers is handy for handling the specimens. You probably already have some in your vest.
If you want to take specimens home, you'll need vials. You can buy the professional kind from a scientific supply house. Possibly, you can get some from a floristflorists use them to keep cut stems wet. These are a rigid plastic that can fracture, but I'll bet they're cheap.
There are various fluids used to preserve specimens. I don't keep pets, so you'll have to find out about this subject for yourself. Search the internet for "insect collection".
Insect collection kits are available commercially. They commonly have a few vials, a magnification device, a collection net, etc. Collapsable, long-handled, collection nets show up in various tackle catalogues. Once again, search the internet for "insect collection".
You've caught your whatever; it's under your fearsome gaze. How do you tell what it is? I recommend An Angler's Guide to Aquatic Insects And Their Imitations For all North America by Rick Hafele and Scott Roederer, Johnson Books, Boulder, Spring Creek Press, Estes Park. Size is five inches by eight a little big for a pocket, but managable. The identification process leads you with questions. Absolutely no previous experience with insect anatomy is required.
After helping you ascertain that what you have is indeed an insect (four simple criteria, e.g. one pair of antennae), it moves on to identifying the life stage (i.e. nymph, larva, pupa, adult). Whichever of those four it turns out to be, you are given the page number of the next key to its identity. What follows are clear descriptions, clear illustrations, and clear instructions about the next key. You will ID that creature.
Several other books are handy to take on the stream; they have been published by Frank Amato Publications in pocket-size:
Not as rigorous in their identification method as the Hafele and Roderer guide, nontheless, these are valuable books. The Schollmeyer books have excellent color photographs of the insects and several flies to imitate each. The organization scheme is by order (i.e. stonefly, caddisfly, etc.) then by species, then by life stage (i.e. larva, pupa, etc.). The descriptions are helpful in identification and contain some natural history interwoven with advice about how to fish the imitations. The Hughes book is a more anecdotal style, but contains good specific information on patterns and their use. The organization shifts between order and species, but it is sensible, i.e.ants, March Browns.
This author, not having read it, but recalling the good reviews, suggests that you also check out Dave Whitlock's Guide To Aquatic Trout Foods, Lyons and Burford, 1982.
Only Captain Kangaroo would have a pocket big enough for Gary LaFontaine's Caddisflies, probably the definitive fisherman's entomology for that order of insects for the forseeable future. Of course, it's not a stream-side book. Maybe you'll want to keep it in the vehicle, though. Mayflies: Angler's Study of Trout Water Ephemeroptera by Malcolm Knopp , Robert Cormier, Mike Lawson (Contributor), Roman Scharabum (Contributor) is another bug "bible"comprehensive, well-done, favorably reviewed. There are more: a quick dash around Amazon.com turned up a number of other books, by good authors, on trout bugs.
An aside: I find the natural history in these books helpful when tying flies.
Begin modestly. Get one of the streamside guides and start turning over submerged rocks; add books and equipment to keep pace with your evolving level of interest.
Igor Doncov's article on food abundance vs. availability ties entomology to fishing strategy.