1. Volunteers have helped in scientific surveys of birds and other organisms for decades, but more recently, the use of the Internet has enormously widened the opportunity for citizen science and greatly increased its practice. There is now a need to share experience of which methods work and which do not. Here, we describe how we planned and executed the Evolution MegaLab, one of the largest surveys of polymorphism in wild species so far undertaken.
2. The aim of the Evolution MegaLab was to exploit the occasion of Charles Darwin’s double centenary in 2009 to mobilize the widest possible section of the general public in Europe to help survey shell polymorphism in the banded snails Cepaea nemoralis and Cepaea hortensis. These data were then compared with historical records to detect evolutionary change that may have taken place in the decades between samples.
3. Records of polymorphism in over 7000 populations sampled throughout the natural range of the two species were captured from published and unpublished sources and added to an online database. These data could be explored by the general public via a Google Maps interface on the project website (http://evolutionmegalab.org). The website contained a welcome page that explained what evolution is and how recent changes in climate, and the abundance of predatory birds (song thrushes Turdus philomelos) might have caused an evolutionary change in the shell patterns of banded snails.
4. A network of collaborators in 15 European countries was formed, with each country responsible for translating the website and associated materials, recruiting volunteers and raising any funds required locally. A total of 6461 users registered with the site, and 7629 records were submitted. We used an online quiz to train users and to test their ability, to recognize the correct snails and their morphs. Every user received automated, immediate feedback that compared their data with nearby records from the historical database.
5. The critical tasks achieved by the Evolution MegaLab that any citizen science project must tackle are as follows: (i) design of an appropriate project, (ii) recruitment, motivation and training of volunteers, and (iii) ensuring data quality.