Matching the hatch with the right fly to catch trout and salmon sometimes involves considerations beyond picking an artificial that looks like the natural in size, color and silhouette.

For example, across much of Maine, a mayfly with the Latin name Ephemerella subvaria emerges in May, and a strange factor for matching this insect makes the species special. It’s gender specific, so the fly pattern for the male has a more slender body than the one for the chunkier female. Most mayflies do not require such a distinction for matching the hatch.

* A Red Quill dry fly originated in the 1930s by the late Art Flick of New York imitates the male E. subvaria dun, which has wings, six legs and three tails that are medium-gray and a slender, mahogany-colored body.

* A Hendrickson dry fly developed in 1915 by Roy Steenrod of New York matches the female E. subvaria dun, which has exactly the same colored wings, six legs and three tails but a chunky, light-pink body with a hint of yellow primrose.

* A Compara-dun Hendrickson dry fly works well for the female in this hatch but not so well for the male — understandable because of the Compara-dun’s chunky, fur-dubbed body.

For some reason, male E. subvaria often hatches at the same time on rivers, and females emerge on a different schedule. Even more bizarre, my home river has predominantly males, and I seldom see females. However, you know they gotta be there to procreate.

Even more complex for hatch matching, the right fly choice may go beyond size, color and silhouette and gender differences, and a red-quill mayfly hatch on the St. George River offers a perfect example.

The St. George’s red-quill insect is a different genus and species altogether than E. subvaria. The insect has darker-gray wings, two tails instead of three and six legs and an ultra-slender, dark-mahogany body. For consistent action on this Mid-coast river, I tie a darker Red Quill with dark-gray wings, hackle and tails and a slender, dark-mahogany body.

The above anecdote provides a perfect example of how matching the hatch works. Folks with that knowledge can become the master of their fate rather than anglers who rely strictly on luck.

When matching flies to forage, serious fly rodders notice a rather bizarre occurrence. If myriad fly fishers start using the same pattern on a particular water, trout or salmon eventually avoid that pattern. I suppose a majority of the fish get stung by the hook, making them think, “Not again, Mr. Fly Rodder!”

In the 1980s, I noticed this phenomenon when spring salmon anglers on the Belgrade Lakes’ Long Pond started using a streamer called “Jerry’s Smelt.” The late Jerry Partridge of Belgrade Lakes village developed this deadly pattern, and it received notoriety in magazines and books.

In April and early May during the mid-1980s, I wouldn’t fish Long Pond without a size 4, 8x long Jerry’s Smelt, but after two or three years, its effectiveness nose-dived.

Here’s another example: In the early 1970s, a smelt imitation called a Supervisor suffered the same fate on the Penobscot’s West Branch below Ripogenus Dam.

These flies come back when fly rodders stop using them for years, so if salmon ever come back into Long Pond as they were in the 1980s and ’90s, I’m sure Jerry’s Smelt will fool them big time.

In the last 12 years, I’ve really gotten into size 20 to 24 blue-winged olive (BWO) hatches, a mid-summer through fall emergence that often comes off at 10 a.m. to early afternoon and offers consistent sport.

My favorite fly for this hatch surprises folks — a caddis emerger with a pea-soup-green body, gray Cul de Canard (CDC) collar and no tails. It fools browns, brookies and landlocks during BWO hatches.

Several years ago, I wrote about this pattern in this column, and a man who owned a fly shop and sold the fly scolded me in a good-natured way, asking me to avoid mentioning this fly in print. Even though he sold the fly, he didn’t want it to get too much notoriety, which would turn fish off.

In the 1970s, the late Ed Reif of Bangor developed the W. B. Caddis, which a bunch of us overused on the Sheepscot River as a searching pattern between hatches. Also, for some reason, Reif’s fly fooled brookies, browns and landlocks during red-quill hatches. Excess use killed it there.

If there is a moral to the story, it’s this: Avoid publicizing favorite patterns. I’ve fished too long and seen the consequences too often to believe that salmonids don’t get spooked by an ultra-familiar pattern.