On some butterfly wings, the “tails” can be more than just elegant ornaments. They are also tools for survival, a study shows.
The tails appear to attract the attention of attacking birds, keeping them away from the more important parts of the butterfly’s body, researchers said on May 25 in Notices of the Royal Society B. The discovery may help explain why winged tails have evolved many times independently of different groups of moths and butterflies.
Evolutionary biologist Arian Chotard of the National Museum of Natural History in Paris is studying the wings of butterflies, swallowtails, which make up the hundreds of species in the Papilionidae family. “Many of these butterflies show tails,” Chotard said. “And we don’t really know why.”
It is known that some species of butterflies with false patterns on their heads or spots on their wings receive more attacks from predators in these regions. And Chotard and her colleagues wondered if the tails were also a target.
Thus, in the summer of 2020, researchers collected 138 butterflies swallow tail (Ifiklid podaliriy) from the wild in Ariège, France. Swallowtails, which are found throughout Eurasia, have two conspicuous black tails on their hind wings with few blue and orange spots that contrast sharply with the yellow, striped coloration of other insects.
Among the collected swallow tails, 65, or 41 percent, had damaged wings, all of which had at least one damaged tail. When all 130 wings in this group of damaged butterflies were counted, more than 82 percent of the wings had damaged tails, suggesting that predators may be targeting spindle-shaped parts.
To test this idea, the team kept wild-caught songbirds called great tits (Sail major) in cells. The researchers then showed the birds mannequin butterflies made by sticking real dovetail wings to a fake body made of small pieces of black cardboard, and filmed the birds’ attacks on artificial insects.
Forty-three of the 59 beak blows, or nearly 73 percent, were on the hind wings. Twenty-three, or 39 percent, of the blows touched both the tail and the colored areas at the top of the rear wing, more than any other area of the mannequin’s body.
Chotard and her colleagues also measured how much force was needed to tear different sections of a swallow’s tail wing. They found that the vein in the tail of the hind wing was the most fragile part of the wing and was probably the most suitable place to break off in the beak of a hungry bird.
Taken together, the findings suggest that swallowtail tails deflect attacks from the butterfly’s vulnerable body to fragile extensions that break easily, allowing the insect to escape, the researchers said. This may be similar to the strategy some lizards use when sacrificing their moving tails to hungry predators.
It is unclear whether there are any costs to losing one or two queues, Chotard said. “You survived, you escaped from a predator, but maybe there is a compromise and maybe your flight will be [slower]”
Some moth tails can repel attacks by echoing bats (SN: 16.02.15). “We now have evidence that butterfly tails provide a similar benefit against visual predators,” said evolutionary biologist Juliette Rubin of the University of Florida at Gainesville, who was not involved in the study.
Future work to determine the benefits of queuing survival could be the next step, Rubin said. “It would be informative to see how live swallowtail butterflies – both with and without tails – cope against bird predators.”