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Bird poop -- the best disguise ever

A larva of swallowtail butterfly Papilio xuthus changes its body pattern at the 4th molt. The juvenile larva resembles bird droppings (left) in its fourth developmental stage, or "instar," and its host leaves (right) during its final instar. [Image courtesy of Ryo Futahashi]

Swallowtail caterpillars are masters of deception. In their early stages of life they look just like the black and white goo of bird droppings, and just before becoming butterflies they resemble the green leaves they live on.

Scientists have now identified the hormone responsible for this change in appearance. They report their discovery in the 22 February issue of the journal Science.

The levels of this hormone, called juvenile hormone, drop in the caterpillars at the end of their black and white bird-dropping stage. And, this drop seems to signal the caterpillars to transform into their green, leaf-mimicking stage, the researchers found.

The scientists, Ryo Futahashi of the University of Tokyo and Haruhiko Fujiwara of the National Institute of Agrobiological Sciences, report that juvenile hormone seems to regulate not only the caterpillars’ overall color patterns but also the development of other features, such as the growth and later disappearance of bumpy structures on the caterpillars’ surface.