July 2nd, 2007

Bug Latin Revisited
By Neil M. Travis, Montana

Alas it is true, the brown trout that is sipping insects from the surface of your favorite trout stream does not know the difference between Tricorythodes minutus or Tricorythodes stygiatus. That rainbow trout that is slashing at the fluttering caddis flies does not know the difference between Brachycentrus americanus or Brachycentrus occidentalis. Given the relative size of the brain of most salmonoids it seems unlikely that they posses the necessary mental cognition to make the distinction even if they had a desire to do so.


Alas it is equally true that anglers can, if they desire, make the distinction between many of the various forms of insects. When JC wrote about this subject recently he mentioned a 'fishing buddy' that enjoyed making the distinction between the various species of bugs and things. I am that 'fishing buddy'.. While taxonomy, the orderly classification of plants and animals according to their natural relationship, is not everyone's cup of tea it nonetheless has a place and a purpose, even in the world of fly-fishing. Many of the older writings that described various types of insects used common or local names; names like March Brown, Blue Dun, Pale Watery Dun, Great Red Spinner, and similar names. Today it is nearly impossible to connect those names to any known insect thus rendering the information about these insects useless for modern day anglers. It would be nice to know if the Blue Dun hatch described by some 19th century writer is still a viable hatch, and if the patterns they concocted to imitate it would still be effective. Such is the importance of taxonomy.

All that having been said, it is totally true that trout cannot tell the difference, and on a practical level if you call a fly a Blue Dun, a Pale Watery Dun, or just a gray bug makes little or no difference. If the fly you are using catches fish you can call it whatever you want. However, I might purpose that a bit of scientific knowledge may enhance your enjoyment of the sport of fly-fishing, and might even increase your success.

Trout anglers deal with two basic types of insects; aquatic those that live in or hatch from the water, and terrestrial those that live on land and end up in or on the water. In the first group we have four basic types; mayflies, caddis flies, stoneflies, and midges. There are other types of aquatic insects upon which trout feed, but these four basic types are the most common. It will enhance your ability to catch trout if you can tell the difference between the four basic types of trout stream insects.


Mayflies are the insects that most dry fly anglers associate with fly-fishing, especially for trout. Mayflies range in size from 2 to 3 millimeters to giants measuring 40 to 50 millimeters. [One millimeter equals 0.039 of an inch] They come in a variety of colors, and are mostly found in cold water with high levels of oxygen. They spend most of their lives as nymphs in streams or still waters, and swim to the surface to hatch into the winged form. Most species undergo a second molting process before they are capable of breeding. Anglers call the hatching insects 'duns' and the egg laying adults 'spinners.' All that you have to know about mayflies is that the wings of the adults are held upright over the body when the insect is at rest, much like a butterfly. If you see some insects floating on your local trout water with wings held upright over their bodies it is likely that you are observing a hatch of mayflies.


Like mayflies, caddis flies spend most of their lives underwater. Unlike mayflies, once they hatch they do not undergo any further transformations. Caddis fly larvae look like worms, and many of them construct cases that serve as protection during this stage of their lives. Like butterflies, when the larvae are fully-grown they spin a cocoon, usually inside their case, and make the transformation from larvae to adult. When they hatch they swim vigorously to the surface and rapidly fly away. Some species run across the surface of the water after they hatch, which makes for some exciting strikes. Caddis flies fold their wings over their bodies like a tent, and have a strong resemblance to terrestrial moths. During the course of the season many trout waters will have very heavy hatches of caddis flies, making them one of the more important insects for the trout angler to be familiar with.


In general, stonefly nymphs require waters with very high oxygen content, which limits most species to very cold water. For most anglers stoneflies are the least important aquatic insect, and except for such well-known hatches as the famous Salmon Fly, Golden Stone, and the diminutive Yellow Sally most anglers will seldom encounter a fishable hatch of these flies. Stonefly nymphs are squat flat insects ideally adapted to the type of water where they are generally found. When they are ready to hatch most species crawl to the bank, emerge from the water, and hatch on dry land. They only return to the water to lay their eggs. Stoneflies fold their wings flat over their back when at rest. Some species of stoneflies, like the Salmon fly, can be two inches long, and when they are available can provide some of the most outstanding dry fly fishing. Some of the largest trout that are taken on dry flies are caught on patterns imitating these flies.

On most trout waters midges are the most common aquatic insects. They can be found hatching every month of the year unless the water is completely frozen. In the course of the year they hatch in untold millions, and provide a very critical food source for many species of fish. Midges belong to family of insects that include such favorites as mosquitoes, black flies, no-see-um's, and houseflies. Many an unfortunate midge has been slapped flat by someone that thought it was a blood-sucking mosquito.

Midge True midges are benign, having no biting mouthparts with which to extract your blood. While most midges are quite small, lake midges, often called Chironomids, can be quite large with some imitations being tied on a size 10 hook. If you can identify a mosquito you know what an adult midge looks like. The larval form looks like a worm, and the pupa resembles a worm with a large head. The adults hatch from the water, form large swarms over nearby areas, and return to the water to lay their eggs. The larva and pupa are of greatest importance to anglers, but fishing to trout rising to the adults is some of the most demanding and exacting dry fly angling available.

Terrestrial insects include everything else, and to describe them all would require several large volumes. If it lives on land, finds its way into the water, a trout may eat it, and if you can imitate you just might catch them.

If you want to successfully imitate a specific insect that you see trout feeding on it's really quite simple. Pick one up, look at it, notice its size and general color, watch how it acts on the water, and then fish something that has that general shape and overall color. If your imitation looks edible to the trout, and it is presented properly the trout will likely take a shot at it. If you know the name of the bug good for you, if you catch the trout and don't have the slightest idea what type of bug you were imitating that's even better, unless you are going to write a book about trout stream insects. ~ Neil M. Travis, Montana/Arizona

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