May looms just around the corner -- dry-fly month in central and coastal Maine. For many of us, winter daydreams about open-water fishing center on May when mayflies begin hatching.

Despite the late spring, the current string of rainless, sunny days has rivers, streams and brooks changing fast in the bottom third of the state. Water temperatures are rising and flow levels dropping with great rapidity, so an emergence aquatic-insect should erupt right on schedule in early May.

I'd bet my life savings on that last statement, and it's particularly true on brooks, streams and small rivers. It takes longer on big rivers such as the Kennebec for the water to warm to 50 degrees Fahrenheit and activate insects, but smaller drainages heat up in a hurry.

This spring will be one of the few years when ice-out mania in ponds and lakes and mayfly hatches in flowing water will darn near coincide with one another. In most springs, hatches in rivers, streams and brooks begin in earnest after the ice-out fishing flurry in still water, but these annual events will overlap in 2008.

Dry-fly fishing has everything to recommend it, too, beginning with these thoughts about the advantages of fishing a floating imitation:

• Dry flies can be ultra-effective because the angler can see the feeding salmonid's rise ring and also know exactly where the dry fly is floating on each presentation. That assures the caster that the fly is on target precisely where the hungry maw awaits. Folks with submerged lures casting to a bottom-hugging trout or salmon can only surmise that the presentation is passing the fish's nose.

• If you offer a rising salmonid a fly imitation that matches the natural in size, color and silhouette and the movement of the feathered creation matches the aquatic insect that the fish are targeting, chances are excellent of getting a strike.

Often, "duplicates the movement" means a fly dead-drifting on the surface because that's how most mayflies behave -- a natural float on the meniscus.

Sometimes, the current pulls on the line or leader and moves the fly faster or slower than the flow. Fly rodders call this "drag" and particularly notice it when the fly create a V-shaped wake. However, a subtle, barely perceptible drag frightens fish just as much.

As a general rule with limited exceptions, when fishing a mayfly imitation, the fly should be traveling at the exact same speed as the current. A trick helps me make sure everything is copasetic, too. I watch something floating beside my fly -- a fleck of foam, a leaf, piece of grass or whatnot. Are they both going at the exact same speed? If so, it's a correct drift.

If the fly moves even slightly slower or faster, I change the angle or get closer to shorten the cast, which often eliminates the subtle drag.

My childhood on the Sheepscot River made me a dry-fly angler, a country boy who had no relatives who fly-fished. Here's how it happened:

My uncle, a captain in the merchant marines, gave me a fly rod when I was five years old, and it became my tool of choice. From that age through my mid-teens, I used worms in April's high water, which worked gangbusters, particularly the last two weeks of the month and into early May.

Then, salmonids switched over to surface insects and would consistently ignore worms. It dawned on me that in May when rise rings dotted the surface, success depended on using dry flies.

Through trial and error, I learned to match imitation flies to aquatic insects and in my very early 20s read an article in an outdoors magazine about how challenging and difficult it was to catch fish on dry flies.

"Wow," I said to a friend, "if this writer thinks it's hard to take trout on dry flies, he ought to try catching 'em with worms on the Sheepscot in mid-May."

This coming month, one favorite hatch goes by the colloquial name "red quill" or "Hendrickson," but the scientific name is Ephemerella subvaria.

This aquatic insect lives in cold, gravel-bottomed rivers with some rubble. "Cold" is relative, though, and some rivers and streams with red quills and Hendricksons don't hold salmonids in the summer because of warm water.

Interestingly, Red Quill names the fly that imitates the male and Hendrickson the female. The two genders look so different from one another that fly rodders use a different imitation. The male has a mahogany-colored, slender body and the female pinkish and chunky. Both have smoky-gray wings, tails and legs.

This topic of identifying red quills and Hendricksons by species can get a little complicated, though, and here's why:

Tom Seymour and I fish a trout stream with a silt bottom. "Red quills" hatch there, but it's not E. subvaria. The classic Red Quill dry fly just happens to imitate it. In short, Red Quill and Hendrickson dry flies imitate many different species, particularly in still water.

According to Tom Ames, an expert, fly-fishing entomologist who wrote Hatch Guide for New England Streams (Frank Amato Publications), Maine has more mayfly species than any other state. Folks who live here should take advantage of the bounty and fish dry flies, emergers and nymphs, which really start working in May in coastal and central Maine.

Ken Allen, of Belgrade Lakes, is a writer, editor and photographer.