Realtime social networking service rapidly reveals distributions of non-indigenous land snails in a European capital

We utilized a social media website (Facebook) to gather information from citizen scientists on their observations of the introduced large land snail species Cornu aspersum, and Helix lucorum in Budapest, Hungary. In a Facebook post we presented the project to reveal where the two species occur in Budapest, together with an identification guide which included images. In this study we compiled information received in the two months following the Facebook post. We obtained 44, 92 and 105 locality observations of H. lucorum, the native H. pomatia and C. aspersum, respectively in the city, mostly within five days after the post. Our Realtime Social Networking Service (RSNS) method, which included intensive communication with citizen scientists, revealed that C. aspersum was spread in most areas across Budapest, except for the Buda region west of the Danube where H. lucorum dominates. Their distributions overlapped with each other only in small ranges. We found that no specimens of these non-indigenous species were present in the collection of L. Drimmer, who extensively collected land snails in the city in the early 1990s. Accordingly, the two non-indigenous species most probably established their current distributions in Budapest in the last 30 years. Our study demonstrates that RSNS method efficiently and rapidly reveals distributions of relatively large animal species in city areas and provides a dependable basis for further research.