They must be pretty tough if they live in the snow. So thought John Hinckley when, while sleigh riding with his family, he found snow covered with what turned out to be an infestation of snow fleas.

They are, in fact, miniscule bugs that are invisible most of the year, living on the ground and eating decaying organic matter.

But occasionally, tired of a long, cold winter, when the sun comes out to warm the snow, they come to the surface and, well, hop -- up to four inches high.

And on rare occasions, as happened last week when Hinckley and his children went into their hay field to sleigh ride behind a 4-wheeler, drifts of the black bugs appear, hopping and jumping.

Hinckley was startled, and then alarmed.

"I had no idea what to think," he said. "I thought that's just what I need around here, another pest."

Hinckley, 62 years old, has always lived on his 500-acre family farm, a few hundred feet from the Utah Lake dike, and said he had never seen anything like the swarm in all his decades in the fields.

He scooped samples and took them to the Utah County branch of the Utah State University Extension Service, where experts identified them as harmless, beneficial insects that occasionally put on surprising winter spectacles.

It's unlikely that many people would find a swarm of them in their backyard, for example, if they went looking, said Julia Tuck of the extension service.

Driving into his snow-swamped hay field in a lugging 4-wheel-drive truck on Friday, Hinckley was able to locate a pocket of the bugs deep in the field. A few were still alive, crawling sluggishly, but most had died. From even a few feet away, the thickest layers of them look like a little black dust or ash on eskers of snow.

A week ago, the bugs were so thick that Hinckley was able to scoop some without snow into a glass jar. They soon died, he recalled. Another group, scooped into another jar with snow, lived several days.

As it turned out, the snow-loving bugs, known scientifically as Hypogastrura nivicola, may be more important than they appear. According to Canadian media reports, a new antifreeze protein has been discovered in the bugs that may be able lengthen the transportation time of human organs to be used for transplants.

Describing them as simple, ancient, almost pre-insects, Tuck said on rare occasions black masses up to half an inch thick of the bugs might be found on a pond, though she knew of no such local reports.

Under a microscope at the extension service lab on Friday, the insects looked like potato bugs with black scaly armor sparsely covered with glassy white hairs.

"They happen to do nothing but nice things," Tuck said, noting that if residents should happen upon a swarm of them, they should not be alarmed.

They are probably called snow fleas because they jump like fleas, but they are not true fleas and pose no danger to humans or pets, she said.

"You will not come out and find your cat gone," she said with a laugh. "Normally, they would be under the snow. When the sun warms up the snow, sometimes they come up, and there are thousands and thousands all over and you can see why [Hinckley] got a little worried. He probably thought he was going to be attacked."