The fly question hovers over us like a mosquito, as we stand knee-deep in trout water, fly box in hand and rod tucked under an arm – hearing the slurps and splashes of the surface-breaking trout on the feed.

The fly question hovers over us like a mosquito, as we stand knee-deep in trout water, fly box in hand and rod tucked under an arm – hearing the slurps and splashes of the surface-breaking trout on the feed.

Our most well-thumbed hatching charts have been tuned and added to for years. Scientific and detailed streamside diaries, kept for decades by experts in adjacent watersheds who form consortiums of information – all add to the ever-growing entomological catalog of the life-cycle of the stream-borne emergers.

Why all the interest?

Simply because waterborne bugs constitute the bulk of a trout’s diet.

Figure out the trout’s daily menu and an exciting, adrenaline-charged time in the water is almost guaranteed to the angler.

But the variables continually keep the answer just out of reach, like trying to catch that mosquito in the dark.

Outside the different factors of equipment, knowledge and skill, which fishermen as a breed tend to amass, the streams themselves each have unique characteristics.

And these differences have a direct bearing on our success astream.

Some waters, such as the fabled rills of the Catskills have been analyzed by some of the best fly-fishermen. Every free stone turn and slate drop-off on the Beaverkill, Espopus, Neversink, and many others have had tens of thousands of infinitely precise presentations offered there each year.

And these tiny offerings have been presented for over a century. The pilgrimage from metropolitan areas in New York and New Jersey has provided not only the fanaticism, but also the dollars to spawn a market that supports bonafide professional fly-fishermen.

And most drive back to their urban haunts a bit humbler, a bit beaten, and yet with a bit more resolve to pick up the challenge on the next weekend.

These chest-wader wearing pilgrims hit the cool headwaters of the Delaware watershed in the Catskills, attempting to gambit the educated trout in the no-kill zones there.

By the time any normal trout would have long since spanned a frying pan, the finicky fish of the eastern freestone streams have been caught and released before. So their mouths often show the telltale red-pink mark from a prior hook prick.

These trout soon matriculate to the super-fussy level. There, all but our most perfect offerings will not get as much as a sideways move from the ever-attentive trout’s holding pattern.

And that’s frustrating.

And that’s why we so often stare at our fly boxes with our rod under our arm while standing knee deep in trout water.

And different watersheds each have their unique variations in color and size, not to mention population and importance of various aquatic insects.

May flies, caddis flies and stone flies are the three main types of aquatic insects and together make up as much as 90 percent of a trout’s diet – especially in the late spring and summer. And that doesn't count the land borne bugs.

As the water temperatures climb through May, the various stages of the insects begin to accelerate. And as the temperatures hit the upper 50’s F., the streams become a virtual caldron of metamorphisizing insects.

Nymphs of all varieties explode, ripping out of their shucks in an ever-increasing complex hatch as the water temperatures reach into the 60’s. They are picked off by the trout as they struggle to the surface. And this is when the subsurface wet fly is in its glory.

If they break through the surface tension and ride for more than a few seconds, chances are great that they will be gobbled by the rising trout.

Here, the dry fly rules.

If the flies in fact fly, and make it to the air, the flies are anything but safe as cedar waxwings, swallows, bats and dragon flies take the place of the predators of the water.

And if they do make it to the safety of the trees, then after a final molt, the insects must face the dangers of air and water again when they return to the waters of their origin in fulfillment of the reproductive cycle.

But what the insects have working for them sometimes is the apparent selectivity of the trout.

Often big mayflies float undisturbed over the riffles and danger-laden undercut banks where lunkers lurk.

For reasons known only to fish, trout will sometimes choose a smaller variety of insect – even one which is appearing in fewer numbers, rather than a big, juicy, bug that coats the surface of the water.

The answer to this question of selectivity  still remains veiled and part of the mystery of fly-fishing.

Oh, once in while trout can be fooled by virtually anything.

But when a major hatch is on the water and a corresponding crescendo of rise forms and slashing splashes dimple the water in an ever-increasing frequency, a fisherman knows this is the time he has longed and dreamed for, if not lived for.

It’s called the hatch.

And here – of all places – he wants everything to be right.

And often we are close and able to catch a few. But all too soon the hatch is past its peak. The frequency of insects on the surface has dropped off and the activity of the trout has decreased at the same rate.

And that lunker has alluded us once again.

After years of fishing my native and still favorite trout stream, the Genesee River, I’ve noticed a distinct difference in some of the important emergers.

Flies tied in order to duplicate the Catskill or Delaware watershed borne insects are not as suitable as they could be for the waters of the upper Genesee.

They are often off a bit in color, and size, too.

We know that populations as a whole of may flies, stone, and caddis flies, which are important in one section of the state, can be non-existent or greatly diminished in another.

Even on the same weekend, different streams offer their own unique signature, written by tens of thousands of insect wings, above and below the surface.

And read by the perplexed angler, staring into his fly box while midstream with his fly rod tucked under his arm.

Oak Duke, publisher of the Wellsville (N.Y.) Daily Reporter, writes a weekly column. Contact him at publisher@wellsvilledaily.com.