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| The Virgin Islands swallowtail butterfly Battus polydamas thyamus has no ‘tails’ on its wings. |
Battus polydamas butterflies are fairly common in the Caribbean. However, they have an uncommon status because they are included in the large ‘swallowtail’ family even though they don’t have the characteristic ‘tails’.
In fact, when I first saw one of these butterflies on St. John, its back wings had been bitten off, so I didn’t realize that it was missing the tail-like extensions characteristic of other types of swallowtail butterflies.
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| Sometimes predators bite off the bottom of a butterfly‘s back wing. |
In the northeast United States, I have seen other swallowtail butterflies that have their namesake projections clearly sticking out from the bottom edges of their back wings.
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| This US Eastern Tiger Swallowtail shows off its distinctive tail extensions. |
The swallowtail name refers to birds like Barn Swallows that have long, thin, outside tail feathers, sometimes called ‘streamers’. These thin feathers can improve their ability to maneuver quickly in flight, especially when they chase flying insects. Interestingly, female Barn Swallows seem to be attracted to the males with longer tail feathers — even when the tails get so long that they are no longer helpful for hunting maneuvers and instead create extra aerodynamic drag on the birds’ wings.
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| Barn Swallows have forked tails with long outer feathers on the edges. |
Swallowtail butterflies probably deal with the same issues of lift and drag as barn swallows, and having tails may actually help them glide smoothly over flowers. But the butterflies’ swallowtails are all pretty much the same size, so probably aren’t a factor for sexual selection. They might be helpful in distracting and scaring off predators, though. When threatened, butterflies sometimes will quickly flick their wings open and closed, showing surprising flashes of bright colors.
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| Battus polydamas thyamus butterflies have red-orange spots on the undersides of their wings. |
And when birds come up behind swallowtail butterflies and grab onto their back wings, it might be helpful to have a skinny tail part that tears off, to help the butterfly escape and survive — like when lizards lose their tails to predators but escape with their lives.
However, the tailless Battus polydamas butterfly I saw with the bitten wing seemed to have managed to survive okay too.
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| A Battus polydamas thyamus butterfly has white markings along the tops of its wings. |
Meanwhile I can’t help wondering why a no-tail butterfly is classified as one of the swallowtails.
The scientific names we use originally came from a classification system designed by a Swedish naturalist named Carl Linnaeus in 1735. The groupings were based on similarities and relationships he observed in nature. Of course, since then classifications of life forms have become more complex and fluid. New species have been discovered, and more is known about interconnections in evolutionary history, including through DNA sequencing.
The VI no-tail butterfly is identified as:
Class: Insecta;
Order: Lepidoptera (which covers both moths and butterflies);
Family: Papilionidae (butterflies);
Subfamily: Papilioninae (swallowtail butterflies);
Genus: Battus (swallowtail butterflies in the Americas associated with Aristolochia plants);
Species: Battus polydamas (tailless Battus butterflies);
Subspecies: Battus polydamas thyamus (tailless Battus butterflies living in Puerto Rico and the Virgin Islands).
A species represents a set of individuals that can mate with each other and reproduce. Usually a scientific name provides first the genus and then the species. A third name indicates a subspecies with some physical variations, often related to geographical differences, such as living on different islands. Many members of the various subspecies listed under Battus polydamas are located on different Caribbean islands, and they are all tailless. The subspecies found in Puerto Rico and the Virgin Islands is named ‘thyamus’.
I learned that an important link between the tailed and tailless members of the Battus swallowtail butterfly genus is co-evolution with their host plants in the Aristolochia family. These plants are woody, climbing vines often called pipevine or Dutchman’s pipe because of the shape of their flowers. They sometimes have been cultivated for medicinal purposes, but also can be toxic. The Battus butterflies lay their eggs on these vines and the caterpillars ingest the toxic chemicals, making themselves and the adult butterflies poisonous to predators.
Another (weird) attribute they share is that their caterpillars have bright orange organs called osmeteria that they can pump up and extend out of their heads like forked tongues, while also emitting a foul smell — as a way to ward off potential predators. Sounds like something we all could use.
So due to their common evolutionary history, different types of swallowtail butterflies share some behaviors and physical attributes unrelated to the tail or no-tail distinction.
I think that’s a good reason to come up with a more inclusive name for the group. Maybe something like ‘stinky, orange, fake forked-tongue caterpillar heads’ would be more appropriate.
