He was an honors graduate of North Central College in Illinois, received his doctorate in experimental biology from Harvard University in 1936, and immediately became notable in cancer research at Haskins Laboratories.
This interest led to research at New York's Museum of Natural History, and Zahl published Blindness: Modern Approaches to the Unseen Environment (1950), Flamingo Hunt (1952), and Coro-Coro: World of the Scarlet Ibis (1954).
His subject matters included coral reefs, volcanoes, giant frogs, carnivorous plants, seahorses, scorpions, man-of-war jellyfish, piranhas, hatchetfish, butterflies, and slime molds.
When Zahl died of prostate cancer in October 16, 1985 in Greenwich, Connecticut at the age of 75, the National Geographic Society headquarters hung the American flag at half mast in his honor.
Eda Zahl, an actress who appeared on stages in Washington and elsewhere during the 1960s and 1970s, and who assisted her husband during his career with the National Geographic Society, died October 25 at her home in Greenwich, Conn. She was 86.
She appeared on a National Geographic magazine cover in 1959, her family said, in a photograph taken by her husband that showed her examining coral collected from reefs near the Hawaiian islands.