Since Charles Darwin, biologists have pondered the mystery of "mimicry butterflies", which survive by copying the wing patterns of other butterflies that taste horrible to their predators, birds. 

This undated handout photo released by the CNRS shows butterflies, Melinaea mneme (top) and Heliconius numata. The mystery of how a butterfly has changed its wing patterns to mimic neighbouring species and avoid being eaten by birds has been solved by a team of European scientists.

The answer, according to a study released on Friday, lies in an astonishing cluster of about 30 genes in a single chromosome. 

"We were blown away by what we found," said Mathieu Joron of France's National Museum of Natural History, who led the probe into what is being called a "supergene". 

"These butterflies are the 'transformers' of the insect world," said Joron. 

"But instead of being able to turn from a car into a robot with the flick of a switch, a single genetic switch allows these insects to morph into several different mimetic forms. 

"It is amazing, and the stuff of science fiction. Now we are starting to understand how this switch can have such a pervasive effect."