University of Bristol researchers found Heliconius hewitsoni can live up to 348 days after maturity, versus 14 days for the closely related Dione juno.
Grip-strength tests in Panama showed older Heliconius hecale performed about as well as younger butterflies, while the shorter-lived Dryas iulia declined with age.
Pollen feeding had been a leading explanation because Heliconius butterflies eat protein-rich pollen rather than just nectar, a diet unusual among butterflies.
Diet alone did not explain the gap: Heliconius hecale still outlived relatives by a significant margin when pollen was removed, pointing to built-in biological differences.
The finding gives scientists a rare side-by-side comparison of closely related insects with sharply different aging patterns, offering a new model for longevity research.