Evolution in action has been observed in snails by European members of the public taking part in an online science project.

More than 6,000 people from 15 European countries took part in the Open University study, Evolution MegaLab, launched in April 2009 to mark the 200th anniversary of Charles Darwin’s birth. Participants were asked to report sightings of banded snails to the MegaLab project via a website address.

More than 7,600 new observations were made in 2009 which were added to historical data collected between 1950 and 1990.

The aim was to find out whether snails had evolved in the past 40 years in response to changes in temperature.

The findings, published in the online journal Public Library of Science ONE, identified an unexpected evolutionary change.

Over time, larger numbers of snails were seen with a single dark spiral across their shell. Simultaneously there was a decrease in the frequency of unbanded shells.

Open University professor of ecology Jonathan Silvertown, who devised the Evolution MegaLab, said: “This is one of the largest evolutionary studies ever undertaken.

“Through mass observation we wanted to give the general public, including families and school children, the opportunity to do real science and to experience the fun and excitement of discovery for themselves.

“Finding unexpected results is what science is all about.

“Exactly what caused the change in bandedness is still a mystery. It does not appear to be related to climate change and researchers suspect it may be due to a decrease in bird predation or some small-scale environmental change. But exactly what has gone on is food for thought.”

Scientists had also predicted snail shells becoming lighter coloured to prevent overheating in sunlight. However, this did not happen except in the case of snails living among sand dunes where shelter is harder to find.