Fossil of stick insect is oldest example of an animal whose shape evolved to fool predators


Fossils found in China show a stick insect, left, that looks similar to the leaves of a plant, right, from the same era. (Reuters)
March 24

Sometimes it is better not to be noticed.

A number of insect species look so much like sticks or leaves that they simply blend in with the foliage, providing camouflage that helps keep them out of the beaks of birds hankering for a bite of bug.

But this is no recent adaptation. An international team of scientists said last week that they have discovered the 126-million-year-old fossil of an insect whose appearance mimicked that of a nearby plant. It is the oldest-known stick or leaf insect that used such natural trickery, they said.

The insect, named Cretophasmomima melanogramma, was found in northeastern China in a rock formation that has yielded many stunningly detailed fossils of creatures such as early birds and feathered dinosaurs.

The researchers realized the insect looked remarkably like the leaf of a plant that grew in the same place at the time. The fossil showed wings with parallel dark lines that, when the bug was in the resting position, seemed to produce a tonguelike shape that could hide its abdomen, they said. The plant had similarly shaped leaves marked with multiple lines.

The researchers think that the insect evolved to look like these leaves — including even their green color — and concealed itself by mingling with the foliage. Females were estimated at about 2.2 inches long; males were smaller.

The findings were published in the online journal PLOS One.

There are roughly 3,200 known species of stick and leaf insects; they belong to the order Phasmatodea, derived from the ancient Greek word for “phantom” a name that reflects their ability to disappear into the background.

Sometimes called walking sticks or walking leaves, they are among the most striking creatures in the insect world, developing unusual shapes to avoid detection by predators.

One Malaysian variety, Chan’s megastick, is the world’s longest insect, at about 22 inches long.

Cretophasmomima melanogramma lived during the Mesozoic Era, sometimes called the Age of Dinosaurs. Its environment was warm and wet, with a large array of plants. The arrival of insect-eating birds and branch-walking mammals gave the insects good reason to develop avoidance strategies, said one of the researchers, paleontologist Olivier Béthoux.

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