Memorial Day weekend, traditionally, is when trout streams are their buggiest, and the Green Drake is preparing its glorious hatch on Central Pennsylvania's limestone-fed gems.

"From the 24th of May to about June 4, hatches are at their peak," said Charles Meck of Pennsylvania Furnace, the author of 13 fly fishing books including "Fishing Tandem Flies" (Headwater Books)," due out in August. "The Green Drake is the luxury hatch, the one everyone waits for, but it's just one of several you can expect to see."

A couple of the big golden mayflies were reported by Meck above Coburn on Penn's Creek, the premier Green Drake stream, a week ago.

"The Green Drake [hatch] starts on Yellow Creek, usually around May 24, then comes to the Little Juniata and Penn's Creek about four days later," Meck said. "The last good Green Drake hatch is on Big Fishing Creek around June 10."

Although warm weather has put hatches back on track, the cold nights that prolonged some of the early season hatches, such as the Blue-Winged Olive, could delay the Green Drake on Penn's Creek by several days, said Steve Sywensky of the Flyfisher's Paradise fly shop in State College. "In 35 years, I've seen Green Drakes as early as May 22 and as late as June 11. I think they'll come the first week of June this year, which is somewhere in the middle."

Green Drakes may be the most visually stunning in terms of size and numbers, but Sywensky said they usually look more exciting to people than to trout.

"Everyone should see a Green Drake hatch. It's absolutely spectacular," he said. "But it can get lost in the jumble of so many other bugs, and fishing it can be disappointing. ... Fish are spoiled rotten this time of year."

Besides the huge variety of mayflies and caddis flies on the water, anglers will find them in various stages, from nymph to emerger to dun to spinner.

"This is a time of complex, compound hatches, especially in [central Pennsylvania], where streams are pretty much unspoiled," Sywensky said. "That means trout can be selective and still feed all day."

On mid-state streams they are likely to include -- all at the same time -- March Browns (size 10), Tan Caddis (14), Craneflies (16), Light Cahills (14), Slate Drakes (10 and 12), Blue-Winged Olives (20) and Sulphurs (14, 16).

"The Brown and Yellow Stoneflies hatch at the same time and go on for a whole month," Sywensky said. "We'll fish the nymphs in fast water and do really, really well."

Anglers on Western Pennsylvania freestone streams also can expect a smorgasbord of bugs.

"All [heck] breaks loose Memorial Day weekend," said Mike Leskowski of Oil Creek Outfitters. "You'll see March Browns, Gray Foxes, Light Cahills, Blue-Winged Olives and Sulphurs. Throw in a Tan Caddis or two for good measure and that just gets you started."

Oil Creek is known for its intense hatches, especially the Sulphur, Leskowski said, and anglers will have to pay attention to the water to know what to tie on, and when.

"Not all of those insects are hatching at the same time and one riffle or hole may be different than the next," he said. "But if a stream supports trout, no matter where you fish, you'll find bugs."

"It's 'the soup,' " said Mark Sikora, who guides with International Angler in Aspinwall. "You'll see some of everything and a lot of it."

Anglers can expect Brown Drakes on most north-central and north-western Pennsylvania streams, most notably Neshannock and Thompson creeks, small Caddises and Midges on Pine, Deer and Buffalo creeks, and size 14 Caddises, Cahills and Sulphurs on Slippery Rock Creek. Buffalo also supports Brown Drakes, but for just a couple of days, Sikora said. Although Dunbar, Laurel Hill and Meadow Run will get Caddises and some Sulphurs and Cahills, the main stem of the Youghiogheny River, a tailrace fishery, is still too cold to support many bugs.

"You're better off with streamers or large attracter patterns, like the Stimulator or Royal Wulff with a dropper underneath, at least until July," Sikora said. "Once it warms up, Caddis are prevalent. So are Slate Drakes and Brown Drakes. The Yough's a good fishery when other streams are done."

Sikora said anglers will find a smattering of Green Drakes on Sugar, Little Sandy and Caldwell creeks, and a decent hatch on Little Mahoning Creek.

"They're not the [size] 8s you'll find on Penn's -- nothing in the world is like Penn's," he said. "Mahoning's [hatches] are spottier and smaller. I'd fish 10s or, better yet 12s."

Midges abound on most streams, especially in Western Pennsylvania, though their size makes them a challenge to fish.

"They're important 12 months a year," Meck said. "If you see them, tie on a little Zebra Midge, a 16 or 18, which is just a black body with fine silver wire and brass bead."

Meck also goes to Sulphurs when there are a lot of different bugs on a stream.

"Fish often prefer a Sulphur over any other mayfly," he said. "The only challenge sometimes is deciding which phase fish are feeding on. That can make or break a fishing trip."

Anglers can get around that, Meck said, by fishing two or three tandem flies, such as an emerger and a dun, or two dries and a wet fly.

"Anglers need to be flexible about what they fish and what time," said Sywensky. "On warm sunny days, in the high 70s, 6 or 7 p.m. to dark is prime time for hatches and rising fish. On overcast or drizzly cool days, bugs can hatch sooner, so you should get to the stream earlier."

Because water has been low, he said, fish have been feeding more often on the surface, which means dry fly fishing may be better than usual.