(Image: Edith Smith, Shady Oak Butterfly Farm)

Is it a snake? No, it’s a caterpillar in disguise, sporting fake eyes and a counterfeit forked tongue. When erected, as seen in this photo, the bright, double-pronged protrusion secretes smelly chemicals to repel predators.

Now Nick Grishin of the University of Texas Southwestern Medical Center and his team are unravelling the secrets hidden in the genetics of these caterpillars, which mature into spectacular Eastern tiger swallowtail butterflies (Papilio glaucus). Their analysis reveals that multiple genes are responsible for making chemicals called terpenes, which get converted into the offensive odours they emit. By contrast, only one or two genes take on the role in the swallowtail’s relatives.

The team also discovered mutations in circadian rhythm genes. The alterations could explain why an Eastern tiger chrysalis quickly matures into an adult butterfly instead of spending the winter in hibernation, as happens with its cousin, the Canadian tiger swallowtail.


With wingspans reaching up to 14 centimetres, Eastern tiger butterflies are revered in their native US, where they have the honour of representing a few states.

Journal reference: Cell Reports, DOI:10.1016/j.celrep.2015.01.026