WASHINGTON - 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 hungry birds hankering for a big bite of bug.
But this is no recent adaptation. An international team of scientists said on Wednesday they have discovered the fossil of an insect in China that lived about 126 million years ago 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 Liaoning province in northeastern China, part of the Jehol rock formation that has yielded many stunningly detailed fossils of creatures like early birds and feathered dinosaurs.
The researchers realised the insect looked remarkably like the leaf of a plant that grew in the same place at the time that was a relative of the Ginkgo tree.
The fossil showed wings with parallel dark lines that, when the bug was in the resting position, seemed to produce a tongue-like shape that could hide its abdomen, they said. The plant had similar tongue-shaped leaves marked with multiple lines.
The researchers think the insect evolved to look like these leaves - even their green colour - and concealed itself from predators by mingling with the foliage.
Females of this insect were estimated at about 2.2 inches (55 mm) long and the males a bit smaller.
"Cretophasmomima melanogramma is one of the grand-cousins of today's stick and leaf insects," said paleontologist Olivier Béthoux of the Center for Research on Paleobiodiversity and Paleoenvironments (CR2P) and the National Museum of Natural History in Paris, one of the researchers.
The findings were published in the online journal PLOS ONE.
There are roughly 3,200 known species of stick and leaf insects, which are members of the insect order known as Phasmatodea, derived from the ancient Greek word for phantom for their ability to seemingly disappear into the background.
They are also sometimes called a walking stick or a walking leaf and are among the most striking creatures in the insect world, developing unusual shapes to camouflage themselves as vegetation to avoid detection by predators.
Some have flattened, leaf-like shapes, with appropriate colour, while others possess cylindrical bodies shaped like sticks or like bark.
One Malaysian variety, commonly known as Chan's megastick, is the world's longest insect at about 22 inches (57 cm) long.
Cretophasmomima melanogramma lived during the Cretaceous, the last of the three time periods that make up the Mesozoic Era, sometimes called the Age of Dinosaurs.
It lived in a warm and wet environment with a large array of plants, dominated by conifers but also featuring relatives of the Gingko, cycas and others.
The arrival of small insect-eating birds and agile, branch-walking mammals provided good reason for insects to develop new predator-avoidance strategies like mimicking the appearance of a leaf, Béthoux said.
The researchers said this insect lacked some characteristics of similar insects seen today, such as a curved part of the front legs that hide the head.