Coleoptera means "sheath wings," a reference to the armored forewings, called elytra, which are either hardened or leathery and , when folded, meet in a straight line down the middle of the back, protecting the membranous hind wings that are used for flight. In flight, the elytra are held perpendicular to the body and function as airfoils, providing added lift. Many species have parallel lines or grooves called striae running the length of each elytron. Although nearly all beetles can fly, most do so only to cover short distances or to reach low vegetation. The rest of their time is spent crawling on or near the ground or on vegetation, trees, willows, or swimming.
Aside from the above information, it is very difficult to generalize about beetles. There are more than 5000 known species of beetles in the North America. They constitute about 40 percent of all known insects, and about one-third of all know animal species. Members of this order range in size from .25mm to 100mm in length, up to 45mm in width, and they occur in many shapes and in all colors, although most are dark. You can find them in every conceivable habitat in North America. It could well be argued that beetles are the most successful organisms on earth.
Importance:
As a fly fisherman, you will most unlikely need to 'match the hatch' with beetles. In fact, you should probably never have to match any of them. You should, however, carry a few beetle patterns, because trout sipping beetles can be selective to something that looks at least a little like the one they're taking, and also because trout sipping anything tiny and stuck in the film will normally accept a beetle pattern if it happens along, even if it doesn't look like anything they're taking. You don't need to have a lot of different beetle patterns, but you should have at least one or two styles in a range of sizes, including some that are tiny.
Like ants, beetles are available to trout when they fall to the water from brush and grass right at streamside. When the weather is warm and the bank water is smooth, trout feeding daintily there may be eating small beetles. Typically the best water to fish beetle patterns are near the bank that has lots of vegetation and the water is somewhat smooth and calm. Beetles are also important when it's a windy and warm, causing small beetles to fall or blown in the water.
Patterns:
Deer Hair Beetles, Foam Beetles, and Hairwing Beetles in black, brown, red, and yellow colors in sizes 16-22.