Japanese scientists have identified the hormone controlling a caterpillar’s amazing switch in appearance from what looks like a bird dropping to what looks like a leaf.

In the early stages of their lives swallowtail caterpillars look like unpleasant bird droppings. Later they change to resemble green leaves, before finally becoming butterflies.

Ryo Futahashi and Haruhiko Fujiwara report in this week’s Science that they have discovered the hormone that governs this change. They found that levels of ‘juvenile hormone’ decrease at the end of the bird dropping phase. Treating caterpillars with a similar compound stopped them from taking the next step and becoming leaf-mimics.

“We found that juvenile hormone works as a switch for the camouflage pattern. That is a novel aspect of this hormone,” Fujiwara, a researcher at the National Institute of Agrobiological Sciences in Japan, told Reuters.

And here’s a quote ripe for being taken out of context by intelligent design proponents. Alfried Vogler of the UK’s Natural History Museum told New Scientist the elegance of having one switch for the whole change was admirable: “If we had to design a system to do this, we would design it in the same way.”

Image top: stages of swallowtail larvae / Ryo Futahashi

Image bottom: larvae in situ / Ryo Futahashi