Every year on the first day of summer, a few outdoor enthusiasts across the United States expose virtually all of themselves to insects, scrapes and thorns for the pleasure of bonding with nature au naturel.

They call it Naked Hiking Day.

"There's no way to explain it until you experience it," said Andrew Williams, 28, a machinist from Warren, Pennsylvania, who first hiked naked six or seven years ago. "It's not about being lewd and crude and all that. It's just enjoyment."

This year, the summer solstice falls on a weekend _ this Sunday. Father's Day.

Hikers who prefer clothes are not happy.

Rangers and police warn that people caught outdoors in the altogether could be charged with indecent exposure. Managers of the Appalachian Trail, where the tradition is sometimes observed by those trekking from Georgia to Maine, also discourage nudity.

"It's just rude," said Brian King, spokesman for the Appalachian Trail Conservancy in Harpers Ferry, West Virginia. "People are out there hiking with their kids and families, and there are Girl Scouts and Boy Scouts."

Law enforcement authorities say they see so few nude hikers, even on Naked Hiking Day, that they don't consider it a big problem.

"It's rare, probably because we have a lot of remote territory out there where one would not be detected," said Capt. Woody Lipps of Virginia's George Washington and Jefferson national forests, which contain parts of the Appalachian Trail.

Ranger Tammy McCorkle, of the state-managed South Mountain Recreation Area in western Maryland, said she hadn't heard of Naked Hiking Day until last year, when visitors reported seeing a group of naked men on the Appalachian Trail. By the time an officer caught up with them, all 10 were clothed; eight received warnings for disorderly conduct after acknowledging they had been nude.

"We're aware it happens on the summer solstice day," McCorkle said. "With through-hikers _ people who hike the trail all in one season _ it's kind of like an unofficial tradition for them."

Nude hiking is a European tradition, too, not that it's any more welcome there. Voters in Appenzell, Switzerland, passed legislation in April banning naked hiking after dozens of mostly German tourists started ambling through their region wearing only hiking boots and socks.

Nude-hiking advocates say they aren't out to startle people.

"I go out of my way to avoid being seen," said Shane Steinkamp, 40, a New Orleans software engineer who blogs about his naked hikes in Mississippi's Homochitto and De Soto national forests on his Web site, theplacewithnoname.com.

"I value the freedom to be able to walk in freedom, but I also accept the responsibility that I should not surprise folks who may take my enjoyment of nature in the wrong way," Steinkamp wrote in an e-mail.

He cited as inspiration passages from Henry David Thoreau, naturalist John Muir and backpacking guru Colin Fletcher that suggest nudity enhances one's appreciation of nature. Steinkamp said he started hiking naked as a boy after skinny dipping on a hot summer day.

"I soon discovered the joys of being a natural animal in my natural habitat," he wrote.

For Williams, the path to nakedness in the woods started at home in rural northwestern Pennsylvania.

"I would walk around the house like that, and walking inside the house turned into walking outside the house, and then short little adventures through the woods. So the next thing I know, I've got a backpack strapped on and I'm walking down the trail," he said.

Williams said he mainly hikes the North Country National Scenic Trail, which stretches from New York to North Dakota.

Both men said they don shoes or boots and a hat if conditions warrant. Sunscreen and insect repellant are also recommended, although Jonathan Jones, a 33-year-old dental hygienist from Waynesboro, Virginia, said there's an advantage to hiking naked in a buggy area: wood ticks on the skin are easier to spot.

___

On the Net:

Hiking Naked: http://www.hikingnaked.com

Appalachian Trail Conservancy: http://www.appalachiantrail.org