For most butterfly species, an adult’s life is brief and—with all due respect to butterflies—unextraordinary. After emerging from its chrysalis, a butterfly will stretch its new wings and set off in search of nectar and sex, spending the rest of its days flitting among flowers, mates, and spots to lay eggs. Within a few weeks, it’ll be dead.
Not so for Heliconius butterflies. Adults in this genus can survive for many months after metamorphosizing, which ranks them among the longest-lived butterflies ever documented. In one case, scientists observed a Heliconius species in a butterfly house living close to a year—25 times longer than relatives in a similar genus. From the human perspective, that’s the rough equivalent of another great-ape species surviving for more than a millennium.
Through their final moments, too, these butterflies maintain an unusual vivacity. In experiments, aged Heliconius feed, flap, and lay eggs just as vigorously as their younger peers; even their muscle strength doesn’t measurably deteriorate, according to a new paper, published today in Nature Communications, from Jessica Foley, a researcher at Tufts University studying aging, and her colleagues. Foley has seen Heliconius butterflies zooming around their cage all day, only to find them dead come nightfall. “I not sure how they’re declining,” or really if they are at all, she told me. The butterflies seem to defy the typical process of aging.
Other long-lived animals have evolved strategies to minimize or counteract life’s wear and tear. Naked mole rats and bowhead whales are particularly good at repairing damage to their DNA; elephants have extra cancer-suppressing genes; bats limit the buildup of cellular waste in their body both by tamping down potentially damaging immune responses and by slowing their metabolism to a near-halt during hibernation. Researchers are still working out Heliconius butterflies’ secret, but they do know that the insects have a very unusual diet: As adults, they supplement sugary nectar with hearty pollen, chock full of fats and amino acids.
[Read: Bats could hold the secret to better, longer human life]
How exactly Heliconius manages to unlock those nutrients is still mysterious. “No other butterfly does it,” Stephen Montgomery, a biologist at the University of Bristol and one of the paper’s authors, told me. Other animals can crush the ultra-tough shells of pollen grains with teeth, jaws, or other similar body parts; butterflies have only a proboscis, a flexible, strawlike structure usually reserved for sipping liquid. Heliconius butterflies do devote an enormous amount of time and resources to finding and processing pollen. The parts of their brain dedicated to learning and memory are much bigger than those of other butterflies, which may help them repeatedly return to the same caches. They’ll then collect pollen on their proboscis and slowly furl and unfurl their mouth parts like a paper party horn—maybe rubbing the grains against one another until they fracture, or relying on special enzymes in their saliva for help—sometimes for hours at a time, then slurp the resulting slurry.
The butterflies’ devotion to this special longevity diet pays off. When the researchers deprived Heliconius butterflies of pollen, the insects’ lifespan dropped by about 25 percent, and they more quickly lost weight as they aged. Those butterflies were also weaker than their pollen-fed kin. But gorging on pollen alone wasn’t enough to lengthen a life. The researchers also fed pollen to a close relative of Heliconius, called Dryas, by spiking their sugar water with it; Dryas typically live for just a few weeks after metamorphosizing, and the pollen didn’t change that. The Dryas butterflies also continued to lose weight and strength as they aged, no matter what they ate. And although Heliconius butterflies fared more poorly when their pollen was taken away, they still lived longer than their Dryas kin.
Outside of their particular pollen habit, the butterflies spend their extra time on the same basic routine until the day they die: They wake early in the morning and forage; after a brief respite to digest, they mate, perhaps lay eggs, and maybe feed once again, then turn in alongside the setting sun. “It’s a great life,” Montgomery said. Compared with many other butterflies, Heliconius butterflies tend to lay relatively few eggs each day—on the order of 10—for months; meanwhile, shorter-lived Dryas butterflies can lay dozens a day. That carries some risk for Heliconius. An adult might, say, get eaten or crushed before maxing out its reproductive potential. But focusing on relatively few offspring at a time may allow Heliconius females to be choosier about where they lay their eggs, increasing the chances that caterpillars will survive, André Freitas, a butterfly biologist at the University of Campinas, in Brazil, who wasn’t involved in the new research, told me.
As they age, Heliconius butterflies remain full of vigor and vim, but no creature can forestall damage indefinitely. The oldest butterflies do “look a bit rubbish,” Montgomery said. The scales on their wings fleck off and can’t be replaced. Their vibrant appendages become tattered and dull. This kind of weathering may be what kills some Heliconius individuals, whose wings get so banged up or shredded that they can no longer fly or escape predation, Montgomery said. At the same time, Freitas has seen Heliconius butterflies “with broken wings, almost colorless, still flying and sometimes still laying eggs.” In general, Foley said, she isn’t sure what ultimately kills these hardy butterflies. They seem to manage to live every day as they did their previous one, up until the moment they die.
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