Why do swallowtail butterflies have long tails?

Related Questions

Translated:

■ English | ■ Korean | ■ Croatian | ■ Norwegian | ■ French | ■ Chinese | ■ Chinese (Traditional) | ■ Spanish | ■ Japanese | ■ Dutch | ■ Italian | ■ Portuguese | ■ Finnish | ■ German | ■ Arabic | ■ Greek | ■ Bulgarian | ■ Chinese (Simplified) | ■ Swedish | ■ Czech | ■ Hindi | ■ Russian