One sun-splashed morning not long ago, I trekked to a central Maine river to fly fish over a blue-winged-olive (BWO) hatch that kicks off at 10 o'clock and hits full blast by 10:15. This time of year on the river, browns and brookies key on this mayfly species at the exclusion of other bugs.

Each morning in late summer and early fall, folks can depend on this tiny BWO coming off without fail, and the emergence lasts two to three hours, depending on weather. Hot, glaring days shorten it.

This particular late morning, a fellow in his 40s was fishing by the road and struck up a conversation. While he talked, we were watching these aquatic insects floating on the meniscus and noting the occasional rises.

BWOs indeed littered the surface, a good year for them, and it disappointed me how few trout were dimpling. Ten years ago on this stretch, browns and brookies filled the pools and runs, but these days, trout densities have decreased considerably as the sporadic rise rings showed. Most of the action occurred in a big pool in the shadow of a bridge.

This guy listened to me say that trout can be ultra-selective in BWO hatches, so success depended on having a fly with the right color scheme, size and silhouette to fool finicky feeders. Usually, I'm less of a bore with strangers but was more or less talking to myself while remembering a jillion anecdotes during this morning event.

When my brief monolog finished, he said in a shy tone, "I don't believe in all this match-the-hatch stuff."

While staring intently at my left shoulder, he went on to say trout have "pea-sized brains" so cannot be that intelligent, which made me smile. His tone was respectful, and I didn't feel like a debate anyway. I shifted the subject to the weather and wandered off a few minutes later.

Trout can definitely be ultra-selective at times, but in my opinion, survival instinct rather than intelligence leads to their picky behavior. To fool this instinct with a feathered creation is a huge challenge.

Something about a certain insect makes the trout key on it, and the reason probably has everything in the world to do with energy expended for x-amount of protein.

For example, tiny insects may float on the surface for long distances while drying their wings, an easy meal for fish even though each bug may measure the length of a mosquito. Instinct rather than intelligence influences trout to concentrate on the abundant forage, despite the diminutive size.

It's like a very hungry person sitting at a table in front of two platters, one mounded with raw celery and carrot sticks and broccoli heads and the other with shelled Maine shrimp accompanied with melted butter. Even though the veggie pieces are much larger, most of us would start on the high-protein shrimp to satisfy our hunger and pop them into our mouth one at a time, each morsel dripping with butter. Later, we'd pick at the carrot and celery sticks or broccoli heads.

Here's another example of picky salmonid behavior. A larger, lethargic mayfly will sporadically dot the surface among a carpet of micro mayflies that are flying off almost immediately after breaking through the meniscus. Even though the larger mayflies number far fewer, they offer an easier target to catch so trout ignore the micro flies.

This month through November, BWOs in size 18 through 28 and smaller, depending on genus and species, will be hatching in Maine rivers, an event that can be so exciting that lots of folks have given up hunting to key on BWO emergences.

These small mayflies have olive bodies and smoky-colored, blue-gray wings, tails and legs. The British have heavily influenced fly-fishing lingo, so we call gray "blue dun," explaining the name "blue-winged olive."

Some BWOs measure in the size 18 to 20 hook range, quite small, and others in the 22, 24, 26 and 28 category would be called micro flies. A size 24 is the size of a mosquito and a size 18 is more like the length of a housefly. Catching 20-inch browns on micro flies ranks up there with Atlantic-salmon fishingÉalmost.

Flies with olive bodies and gray legs, tails and wings match the natural, and it's a good idea to have dry-fly patterns in the Compara-dun, thorax, variant or classic styles. I particularly like thorax flies but Compara-duns run a close second.

For nymphs, a Pheasant Tail in the right size to match the natural works gangbusters. The fact that blue-winged olives in the Baetis and Ephemerella genera inhabit so many of our waters explains why Pheasant Tails are such a popular nymph in this state.

Many BWO species belong to the swimming order of mayflies, so a Pheasant Tail cast quartering across and downstream and retrieved by rolling the line over the fingers fools trout into thinking it's a swimming BWO larva. Before a BWO hatch, this old-fashioned presentation just plain works.

To be honest, I'm not up to par on identifying BWOs species but am learning. It's quite a task, too, because of the immense numbers. My favorite reference is Mayflies by Cormier and Knopf.

Speaking of books, I have the newly published set of Ernest Schwiebert's "Nymphs Volume I: The Mayflies" and "Nymphs Volume II: Stoneflies, Caddisflies and Other Important Insects," which belong in every serious Maine fly rodders bookshelves. Wonderfully written stories as well as technical stuff fill the pages. The books include good stuff on BWOs, too.

Ken Allen, of Belgrade Lakes, is a writer, editor and photographer. E-mail: kallyn800@aol.com