Eisner, who spent his entire professional life at Cornell University, combined the observational skills of Charles Darwin with an inquisitiveness that caused him to look far beyond superficial characteristics. At a 2000 celebration of Eisner's career, biochemist John Law of the University of Arizona said: "Thousands of people can look at the same plant or animal and see the same thing, and there is the one person, like Tom, who comes along and sees something different."
As a child, for example, Eisner observed that the bombardier beetle emitted a chemical that stained his fingers dark brown. As an adult, he used a combination of microphotography, slow-motion film and chemical analysis to show that the beetle had separate sacs in its abdomen, one for hydrogen peroxide and one for a quinone.
When the chemicals are mixed together, they form a boiling, stinky mixture of benzoquinone that the beetle can aim at any potential predator, firing pulses of the hot poison at a rate of 300 per second. "It's a revolvable gun emplacement, so the beetle can fire accurately in any direction," he later said. "And considering that they generate their own ammunition and store everything that's needed to make that ammunition, they're pretty self-contained."
Creationists frequently pointed to Eisner's work on the bombardier beetle, noting that such an elaborate system could not have developed by evolution. Eisner refuted them, however, by demonstrating other species with less complex systems that could be recognized as evolutionary intermediates.
Other insects take advantage of what they can find around them. Eisner noticed that spiders did not eat bella moths that got trapped in their webs but instead cut them free and allowed them to escape. He showed that the larvae of the moths consume alkaloids produced by plants that are distasteful to any predator that might bite the larvae or the moth.
Female moths, moreover, find the toxins an attractive quality in a potential mate. The male passes along some of the toxin to the female, who is able to insert it in her eggs, making her larvae less tasty after their birth.
Eisner deciphered the flashing light code of female fireflies and demonstrated why that species doesn't worry about predators: They, too, don't taste good. And working with his longtime collaborator, Cornell chemist Jerrold Meinwald, he discovered that the same chemicals that made the fireflies taste foul have beneficial effects on the human heart. They also found nerve drugs in millipedes, cockroach repellents in an endangered mint plant and a shark repellent in a marine mollusk.
In other studies, they found that the whip scorpion fends off its enemies with a spray of concentrated acid formulated to penetrate the predator's skin; that some millipedes gas their enemies with deadly hydrogen cyanide that the millipedes store in an inert form and release when attacked; and that aquatic beetles emit a potent repellent when caught by fish, causing the predators to spit them out.
Thomas Eisner was born June 25, 1929, in Berlin. His father, a pharmaceutical chemist, was Jewish and the family fled the Nazis in 1933, moving to Spain. But their sojourn there was interrupted by the Spanish Civil War and they moved again, first to Paris and then to Uruguay.
In 1947, the family relocated once more, to New York City. Eisner enrolled in Champlain College in Plattsburgh, N.Y., and transferred to Harvard University two years later, earning his bachelor's degree in 1951. It was during his senior year at Harvard, while taking an entomology course, that he discovered he could translate his childhood fascination with insects into a career. He studied entomology at Harvard, earning his doctorate in 1955.
Ironically, he had applied to Cornell as an undergraduate but was not admitted. He proudly kept the framed rejection letter on display in his Cornell office.
He became a naturalized U.S. citizen in 1952, the same year he married Maria Lobell, who eventually became an electron microscopist who collaborated with him in his research.
Eisner was a talented pianist who considered a career as a professional musician until his teacher told him he wasn't good enough. He would often sit at an upright piano in his laboratory and play while he thought.
He was also a talented photographer and artist; his film "Secret Weapons" won the Grand Award of the New York Film Festival.
Later in his career, hobbled by his disease, he made artworks using a color photocopier to assemble collages of flowers, plants and insects into pictures of striking beauty.
Among other honors, he was awarded the National Medal of Science in 1994 and the Tyler Prize for Environmental Achievement in 1990.
Besides his wife, Maria, Eisner is survived by three daughters; a sister; and six grandchildren.