On some butterfly wings, the “tails” may be more than just elegant ornaments. They’re also survival tools, a study suggests.
The tails appear to attract the attention of attacking birds, keeping them away from the most vital parts of a butterfly’s body, researchers report May 25 in Proceedings of the Royal Society B. The finding could help explain why wing tails independently evolved multiple times in different groups of moths and butterflies.
Evolutionary biologist Ariane Chotard of the National Museum of Natural History in Paris studies the wings of the swallowtail butterflies, which make up the hundreds of species of the Papilionidae family. “A lot of these butterflies show their tails,” Chotard says. “And we don’t really know why.”
Some butterfly species with false heads or eye spot patterns on their wings are known to receive more attacks from predators in those regions. And Chotard and his colleagues wondered if the cross was a target too.
Then, in the summer of 2020, researchers collected 138 sailing dovetail butterflies (Podalirium hyficlide) from the wild in Ariège, France. The dovetails of the sails – found throughout Eurasia – sport two showy black tails on the hind wings with some blue and orange spots, in stark contrast to the rest of the striped yellow coloration of the insects.
Of the collected dovetails, 65, or 41 percent, had damaged wings, all with at least one damaged tail. When all 130 wings of this group of damaged butterflies were counted, more than 82% of the wings had damaged tails, suggesting that predators may be targeting the thin parts.
To test this idea, the team held wild songbirds called great tit (Paro major) caged. The researchers then showed the birds fake butterflies made by gluing real dovetail wings onto a fake body made of small pieces of black cardboard and filmed the birds’ attacks on the fake insects.
Forty-three out of 59 beaks, or nearly 73 percent, were on the hind wings. Twenty-three, or 39 percent, of the shots simultaneously touched both a tail and colored areas on the top of a rear wing, more than any other body area on the dummies.
Chotard and his colleagues also measured how much force was needed to tear off various sections of the dovetail wing. They found that the tail vein of the hind wing was the most fragile part of the wing and is probably the most prone position to break off in a hungry bird’s beak.
Taken together, the findings suggest that the dovetail tails deflect attacks from the butterfly’s vulnerable body to fragile extensions that tear easily, allowing the insect to escape, the researchers say. This may be similar to the strategy used by some lizards when they sacrifice their detachable tails to hungry predators.
It’s unclear whether there are any costs involved in losing a cross or two, Chotard says. “You survived, you escaped from a predator, but maybe there is a compromise and maybe your escape will be [slower]. “
Some moth tails can deflect attacks from echolocated bats (SN: 02/16/15). “We now have evidence that butterfly tails provide a similar benefit against visual predators,” says evolutionary biologist Juliette Rubin of the University of Florida at Gainesville, who was not involved in the study.
Future work determining the survival benefits of queues could be a next step, Rubin says. “It would be informative to see how live dovetail butterflies, both with and without tails, fare against bird predators.”