This study investigated STEM hobbyists, some who engaged in citizen science projects related to their hobby and some who did not, with the goal of understanding how science hobbies develop over the lifespan. One of the long-range goals of science education is to develop individuals who are knowledgeable about science concepts, processes and understand the nature of science and are able to participate in public decision making related to science. A nation-wide survey was developed and participants included 2119 non-citizen scientists and 745 citizen scientists. Results showed that citizen scientists reported different hobby-related motivations, interests, and experiences than the non-citizen science hobbyists. Citizen scientists had higher ranked scores for sharing information with others (male citizen scientists), educating youth (male citizen scientists), and being influenced by formal and informal educational institutions (male and female citizen scientists). Citizen scientists were more likely than non-citizen scientist hobbyists to report publishing articles about their hobby, speaking to the public, and using electronic media to communicate with other hobbyists. Citizen scientists also reported they had improved science process skills and a better understanding of the nature of science as a result of participating in their hobby. The implications of the study for teachers and informal science educators are discussed.