If all these organisms were compared to a team of Marvel superheroes, the Asian trampsnail would be the Incredible Hulk of the group, said Mr. Hajian-Forooshani, a doctoral student at the University of Michigan.

“It’s a big one and seems to be the most effective at what it does,” he said.

That is in part because it eats huge amounts of the orange spore but leaves the rest of the coffee leaf alone, probably because it does not like the caffeine, Professor Perfecto said. In their experiments, the ecologists took a leaf covered with orange spores and placed on it a single snail, which is no bigger than a thumbnail. Within 24 hours, one snail was able to consume an average of 30 percent of the rust.

The study should not be seen as a call to simply introduce an invasive species into a farm or plantation, Mr. Hajian-Forooshani said. It is not a magic bullet that will necessarily save the morning cup of coffee from rust, he said.

“At this time, it’s a preliminary observation and a simple experiment that we set up,” he said. “But I like the idea.”

The study is a reminder that complex ecological systems can be better, less costly solutions to pests than pesticides or genetic engineering, said Stuart McCook, a history professor at the University of Guelph in Ontario who wrote “Coffee Is Not Forever: A Global History of the Coffee Leaf Rust.”

The study “very appropriately isn’t suggesting that people run around with buckets of these snails and start sprinkling them all over ecosystems,” said Professor McCook, a coffee aficionado who did not participate in the study. “The broader purpose of their work is we need to think of ways to construct the agro-ecosystem to combat disease.”

Professor Perfecto said because the snail is an herbivore it could become a pest for other plants that growers do not want to be eaten.