A Hex, or if your Latin is good, a Hexagenia limbata, is a bomber-size Mayfly that shows up on Maine trout ponds in mid-summer, usually early July. For a trout, they are a turkey dinner with all the fixins — a chance to get the most amount of food for the least amount of effort.

To a trout-loving fly fishermen, a Hex hatch is an adrenaline rush and a sight to behold. In fact, like a solar eclipse or an expanse of northern lights in the winter sky, a true Hex hatch on a trout pond counts as one of those special moments in nature. Truth is, my experience with Hex hatches can be counted on one hand. Still, one July Hex encounter stands out in my memory.

V. Paul Reynolds, Outdoors Columnist

Diane and I were camped at one of Wiggie Robinson’s favorite trout ponds in early July. The fishing had been slow all day. Then just before dark the Hexes began to bust through the still surface of the pond. Soon the pond was covered with these big-winged, lime-green duns. It looked like a flotilla of small sailboats “in irons,” becalmed by the dying breeze.

Blup, Blup, Blup. The feeding began and the pond was peppered with surface-feeding trout dimples wherever you looked. The trout gorged themselves for about an hour. They also took our big White Wulffs without hesitation. Then the Hexes disappeared as fast as they came on, and the fishing slowed accordingly.

There is an ongoing debate among Maine anglers about what to call these big bugs. Anglers who know a lot more about entomology than I do say that most of us misname the Hex, calling it a Green Drake, as in, “Hey, Joe. You really missed it. As soon as the sun went behind the mountain, the pond was covered with Green Drakes. A wicked hatch! Never seen anything to beat it.”

So the question is, I guess, “When is a Green Drake a Green Drake, and when is a Hex a Hex?”

You don’t care? Well, in that case, you’re probably just a casual fly fisher of trout. Those of us whose heroes are fly fishing entomologists like to know our bugs, for that is how you get to know your trout and how best to seduce them.

I put the aforementioned question to Tom Fuller. Fuller, a seasoned fly fisher, outdoor writer, author and aspiring entomologist, has written an informative new book, “Eastern Hatches.” Fishing with Fuller is a learning experience. In late May, after getting skunked at one of my favorite trout ponds, we wound up throwing popping bugs at pickerel and crappies at Hermon Pond. Warm-water angling can be a nice change of pace for trout fanatics. The pressure is off and conversation comes easy. Here is his answer:

“The differences between the Eastern Green Drake (3 tails on the dun) and the Hex hatch (two tails on the dun) are, at best, subtle. The Eastern has mottled wings, the Hex doesn’t have the mottling, but does have veins. Coloration and size really depend on the waters where they’re found and the fertility. The real difference is the double gills found on body segment No. 1 on the Hex. The Eastern nymph has single gills on body segments 1 through 7.”

As Fuller pointed out, when these big bugs are on the water, the fish are really fired up and just about any big pattern will work. Wulffs, a large Adams or a Hornberg never disappoint when the Hex hatch is on. Or, if you are lucky enough to be on the good side of Greenville’s fisheries biologist, Tim Obrey, he may grace your fly box with a timely gift — a lethal fly he ties called a Sexy Hexy.

As always, the best of trout fishing in Maine begins to fade as summer comes on and water temperatures drive the brookies deep into the spring holes. But there is still time, especially because of the late spring and slow-warming waters. The farther north in Maine you go the more likely that the favorable water temperatures will hold a while longer.

And who knows? You might get lucky and get in on a Green Drake hatch during a cloudy, humid day. You won’t soon forget it, if it happens.

V. Paul Reynolds is editor of the Northwoods Sporting Journal. He is also a Maine guide and host of a weekly radio program, “Maine Outdoors,” heard at 7 p.m. Sundays on The Voice of Maine News-Talk Network. He has authored three books; online purchase information is available at www.maineoutdoorpublications.net.