With the help of citizen scientists all across Southern California, we have made many important discoveries, including that of nonnative frogs, geckos, and snakes that had not previously been reported in the region. In the last century, the human population in Southern California has grown dramatically, causing habitat loss and fragmentation. The resulting range shifts and declines of native species have been accompanied and exacerbated by introductions of nonnative species. Citizen science can help fill this gap in our biodiversity knowledge, because it crowdsources data collection by asking the public to photograph organisms they encounter and submit those photos to online databases.