It's a shell of a story: An Illinois grandma picks up a pair of tiny baby turtles on a Florida beach as souvenirs for her grandkids.

Except these aren't your Woolworth reptiles of yesteryear; they're loggerhead sea turtles, a threatened species that can grow to 300 pounds.

They never got that big in the hands of the grandmother. After a 1,500-mile trip back north with the two turtles, she went to a pet store to ask how to care for such a creature. Told she was breaking federal law, the Peoria woman turned the turtles over to the U.S. Fish and Wildlife Service and they ended up at the Shedd Aquarium.

Today, at 5 months old, the two critters will board a plane at O'Hare in what their Shedd escort calls "sea turtle first-class seats'' ­ foam-lined, temperature- controlled boxes -- for the beginning of the end of their excellent adventure.

If all goes right, on Friday the turtles will be dropped into the Atlantic about 10 miles off the shore of West Palm Beach, Fla.

At Shedd, they've been schooled in survival and can forage on their own ­ mostly for small shellfish, said George Parsons, Shedd's director of aquarium collections. They're also young enough so they haven't lost their natural instincts, he added.

The turtles need to be returned near where they were snatched because loggerheads lay eggs where they themselves were born, though Shedd isn't sure what sex the two turtles are.

In some ways, the grandmother may have saved their lives: The survival rate for baby loggerheads is low because of land predators like armadillos and raccoons. In the water, sharks can snack on them.

But Parsons warned against people picking the turtles up, a too-common occurrence in Florida.

"A lot of times, people have really good intentions. They bring them home and want to care for them,'' he said. "But overall, it is a detriment to the turtles.''

Loggerheads can live to be 70 to 100 years old, but these two aren't guaranteed a long life just yet. The worldwide population of loggerheads has in recent years been declining for a number of reasons, including pollution and overfishing.

"Their archenemies are plastic because one of their favorite foods are jellyfish,'' said Parsons. Swallowed, plastic bags or six-pack rings -- which resemble the jellyfish -- can cause intestinal blockage.

In some Third World countries, sea turtles are made into soup and their eggs are sold as a delicacy, added Parsons. "They're facing a lot of problems but coming back.''

Parsons said aquariums typically keep turtles that have been injured by boats, like the loggerhead currently housed at Shedd.

These two Florida-bound reptiles are healthy, and judging from their frantic flipper-flipping displayed for reporters Wednesday, raring to get back to nature.

The hard facts: "Leave things where they lie,'' said Parsons.

While on vacation, "take only pictures and leave only footsteps,'' he said.