It is often assumed that citizen science is inherently participatory in nature. However, citizen science projects exist along a continuum from data contribution to full co-creation. We invited 19 biologists to explore their conceptions of citizen science. Almost all participants defined citizen science as involving non-scientists in data collection. This definition acted as a barrier for scientists who did not see how citizen science could suit their research objectives. While interviewees perceived many societal and experiential benefits of contributory citizen science, deliberate design is needed to realise the full potential of citizen science for public engagement.