NEWBURYPORT - In the 1950s, a red menace was threatening the United States. The only solution, according to a congressman, was total eradication of a devious and implacable adversary.

The enemy? Swarms of red ants and other insects. The weapon? Dichloro-diphenyl-trichloroethane, also known as DDT.

"Insects were a version of domestic subversives," said author Mark Lytle, who wrote "Silent Spring and the Rise of the Environmental Movement," a biography of prominent author and DDT foe Rachel Carson.

Lytle discussed the book in front of 40 people yesterday at the Parker River Wildlife Refuge Visitor Center as part of the final day of the Newburyport Literary Festival.

His talk touched on Carson's visits to the Parker River area more than a half-century ago and how her most famous book, "Silent Spring," helped to end widespread use of the insecticide, which was harming birds, fish, people and the environment.

A Pittsburgh native, Carson became enamored with the sea while working on her zoology master's degree at Woods Hole on Cape Cod in the 1920s. She would end up building her career around the sea and preserving the life within it.

In 1947, Carson applied her style to the Parker River area for a series of government pamphlets on "Conservation in Action." She examined how conservation agents were working to improve black duck populations and was clearly impressed by the number of bird species inhabiting the area.

"Plum Island, Joppa Flats and Plum Island breakwater seem to attract more than their share of rare species," Carson wrote, "and the hope of surprising an ornithological rarity gives zest to often repeated visits."

She went on to write a number of books and articles about sea life, including "The Sea Around Us," which won the National Book Award in 1952 and sold 2.5 million copies.

Lytle described how Carson was looking for a new enviornmental subject. After hearing about the U.S. Department of Agriculture spraying pesticides over millions of acres to wipe out pests like red ants and gypsy moths, she began work on her most famous book, "Silent Spring."

The book reported exposure to pesticides was harming not just bugs, but humans eating the sprayed food and the environment. While Carson said spraying DDT in small doses was acceptable, the overspraying, especially without public knowledge of its impact, was causing terrible harm to birds, fish and other wildlife.

Carson's book was a success, catching the eye of President John F. Kennedy, who formed a commission to look into the damage caused by excessive pesticide spraying.

But it also brought criticisms of Carson. Another government official, questioning what motives a "spinster" had in criticizing the Department of Agriculture, said he "could only conclude that she is a communist."

But while her final book was controversial, Lytle said, Carson's earlier work mainly explained the thrill of the natural world, especially the ocean.

Carson could explain the shores and the deeps, and her fascination was apparent to readers, Lytle said.

"She could take technical terms and translate them into something accessible to a public audience," Lytle said.