Clues within the genetic code of the Eastern tiger swallowtail butterfly (
Papilio glaucus
) explain how it developed a smelly defense against predators.
As caterpillars, swallowtails have a forked organ on their heads that pumps out foul-smelling compounds called terpenes. Sequencing the swallowtail genome revealed extra copies of the genes that the scientists believe are responsible for making enzymes that assemble terpenes.