Public involvement is one of the keys to achieving biodiversity conservation goals. Increasing public involvement in conservation activities requires investigation into what makes people more aware of nature, especially in an ordinary and local context, in their everyday lives. Among the initiatives developed to increase the public’s awareness of conservation issues and individual environmental practices, citizen-science programs are based on an invitation to observe and survey nature. In our study, we examined the consequences of participation in a participative citizen-science program that takes place in an everyday-life context on individuals’ knowledge and beliefs about biodiversity. This program, the French Garden Butterflies Watch, is addressed to the non-scientifically literate public and is run by the French National Museum of Natural History (MNHN). We examined the ways increased knowledge or strengthened beliefs or ideas about biodiversity can foster pro-conservation attitudes and behavior. We explored how repeated interactions with nature influence the development of knowledge in this area, and how these repeated observations of biodiversity become integrated into complex cognitive processes over time and space. We showed that repeated observations of nature can increase individual knowledge and beliefs. Our results brought out three important conclusions: (1) conservation issues must be integrated into a wider network of social relationships; (2) observing everyday nature often makes people consider its functional and evolutionary characteristics; and (3) scientific knowledge seems necessary to help people to develop their own position on ecosystems.