They are on their way.

Except for the chirp of spring's songbirds and an occasional meadow filled with the sounds of anxious spring peepers, it's quiet outside. But that's about to change. Soon enough, we won't be able to escape the noise.

For most of their 17 years, periodical cicadas live an unseen life. They spend their time underground. We don't see them and, more importantly, we don't hear them. But this year is different.

A large population of cicadas known to scientists as Brood 2 is about to climb out of the ground. The last time this brood made an appearance was in 1996. That's when the generation of the critters we're all about to become aurally familiar with started its life cycle.

Now that the weather is warming, the predictable insects are about to put on a big show. All they need is the ground temperature to hit 64 degrees and their internal alarm clocks will sound. When it does, the bugs will emerge, mate and die. We won't see the offspring of Brood 2 for another 17 years.

As outdoorsy folks, the periodical cicada emergence -- which differs from annual cicada varieties that make yearly appearances -- is nothing short of amazing. The scientific community is split on the exact reason the bugs have adapted such predictable schedules.

Some scientists believe it's all about outsmarting hungry critters such as varmints or birds. For most cicada predators, an emergence like we're about to see is a once-in-a-lifetime occasion. That means they can't anticipate the arrival of cicadas. They can't adapt to such a rare food source.

Other experts, though, say it's all about parasites. Parasites have very short life cycles. That means if one generation of cicadas gets infected, it's very unlikely the next will be harmed. Again, it's a defense mechanism.

No matter the reason, the emergence is exciting -- especially for savvy anglers.

Find a fly fisherman and ask him about the trout fishing during a cicada hatch. There's a good chance his eyes will glaze over and a big grin will lift his cheeks. Fishing for trout or even smallmouth bass can be out of this world when cicadas fill the evening air.

As the dying cicadas hit the water, the fish become so enamored with the easy meal that they gorge on them until they can't eat any more. That's when they spit up the last few bugs and keep on eating.

In other words, if you're a fly angler, right now is a great time to start adding some cicada imitations to your fly box. A big opportunity is knocking at the door.

The woods, streams and meadows are quiet right now. But that's about to change in a big way. Mother Nature is about to host a rare show. Don't miss it. It may be a long time until you get another opportunity as big as this one.

-- Andy Snyder writes about the outdoors for The York Dispatch. He can be reached at sports@york