Updated May 26, 2021 at 7:45 PM ET

Eric Carle's picture books were often about insects. Spiders, lady bugs, crickets and of course, that famous caterpillar, all as colorful and friendly as Carle himself. The Very Hungry Caterpillar — probably Carle's best-known work — came out in 1969 and became one of the bestselling children's books of all time.

According to a family statement, Carle "passed away peacefully and surrounded by family members on May 23, 2021 at his summer studio in Northampton, Massachusetts." He was 91 years old.

Over the course of his career, Carle illustrated more than 70 books for kids. He didn't get started on that path until he was nearly 40, but he found great inspiration in his own childhood. Born in Syracuse, N.Y., Carle remembered an early life filled with art, light and walking through nature holding his father's hand.

"I think it started with my father. He took me for long walks and explained things to me," he told NPR in 2007. The elder Carle pointed out foxholes, spiderwebs and bird nests, opening his son's eyes to the beauties and mysteries in a child's landscape. But Carle's immigrant parents decided to return home to Germany — his mother was homesick — and they arrived just in time for World War II.

"All of us regretted it," he remembered. "During the war, there were no colors. Everything was gray and brown and the cities were all camouflaged with grays and greens and brown greens and gray greens or brown greens, and ... there was no color."

Carle was beaten by teachers and shot at by soldiers, and his beloved father disappeared into a Russian prisoner-of-war camp for years after being drafted to fight for the Nazis. The man who wrote The Very Hungry Caterpillar experienced hunger firsthand.

Carle headed straight back to the U.S. after graduating from art school at age 23 and was immediately hired by The New York Times. He fell in love with the impressionists ("color, color, color!"), served in the U.S. military during the Korean War, and, upon his return, moved into advertising.

Perhaps that career helped him prepare for using the simple, resonant language of The Very Hungry Caterpillar. For the book's 50th anniversary in 2019, professor Michelle H. Martin told NPR that The Very Hungry Caterpillar's writing helps little kids grasp concepts such as numbers and the days of the week. ("On Monday he ate through one apple. But he was still hungry. On Tuesday he ate through two pears, but he was still hungry.")

Martin, the Beverly Cleary Endowed Professor for Children and Youth Services at the University of Washington, told NPR the book builds literacy by gently guiding toddlers toward unfamiliar words. For example, when Saturday comes around and the hungry caterpillar binges on "one piece of chocolate cake, one ice-cream cone, one pickle, one slice of Swiss cheese, one slice of salami, one lollipop, one piece of cherry pie, one sausage, one cupcake, and one slice of watermelon," words such as salami and Swiss cheese might be new to 3-year-olds already familiar with ice cream and lollipops.

Carle, who first illustrated the 1967 children's book Brown Bear, Brown Bear, What Do You See? by his friend Bill Martin Jr., wanted The Very Hungry Caterpillar to serve as a literary cocoon for children getting ready for kindergarten. As little kids prepare to leave the warmth and safety of home for school, they're meant to identify with beautiful, soaring butterflies.

"I think it is a book of hope," Carle said in a commemorative video released by Penguin Random House in 2019. Then 89 and retired at his Florida home, he was wearing black suspenders and a blue shirt matching his lively eyes. "Children need hope. You, little insignificant caterpillar, can grow up into a beautiful butterfly and fly into the world with your talent. Will I ever be able to do that? Yes, you will. I think that is the appeal of that book.

"Well, I should know. I did the book, after all!"

In 2002, Carle and his second wife, Barbara, founded the Eric Carle Museum of Picture Book Art in Amherst, Mass, inspired by the picture book museums they'd toured on visits to Japan. Barbara Carle died in 2015. Eric Carle is survived by his sister and two adult children from his first marriage.

This story was edited for radio by Ted Robbins and adapted for the web by Petra Mayer.

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