The garden soldier fly Exaireta spinigera (Wiedemann, 1830) is an Australian member of the family Stratiomyidae Latreille, 1802. It is the second exotic species of this family to arrive in Italy after Hermetia illucens (Linnaeus, 1758), which was first recorded in 1956 (Venturi, 1956). Outside its native range, E. spinigera is known in Hawaii (Hardy, 1960), North America (Swann et al., 2006), France (Lapeyre & Dauphin, 2008) and Italy (Cocquempot & Martinez, 2017). Its status as exotic species in New Zealand is currently uncertain (Derraik & Heath, 2009). Despite the broad distribution achieved, the interactions of E. spinigera within non-native ecosystems as well as its general biology are mostly unknown. Its traits may be generally similar to those of the relatively well-studied H. illucens (Cocquempot & Martinez, 2017), which is not usually regarded as a pest species or a threat to native ecosystems. However, even the impacts of H. illucens on native biodiversity are also mostly uninvestigated (De Groot & Veenvliet, 2011).

The presence of E. spinigera was first recorded in Italy from the Italian peninsula by Cocquempot & Martinez (2017), who cited an observation originally appeared on the Italian internet forum ‘Forum Natura Mediterraneo – Forum Naturalistico’. We attempted to find additional E. spinigera observations by searching in Italian Facebook groups and internet forums with a focus on terrestrial faunistic biodiversity (Table 1). As a result, nine additional records were found among Facebook groups and internet forums (Table 1), revealing the presence of this exotic species in the island of Sicily.

Containment or eradication of invasive exotic species can be virtually impossible or at least very costly if their presence is not detected early enough after their first arrival. Therefore, the development of early-warning systems in Europe is a crucial need (Genovesi, 2005). Many citizen science projects have obtained valuable results in the aim of collecting distribution data on exotic species, including in Europe (e.g., Bois et al., 2011; Zenetos et al., 2013; Adrianes et al., 2015; Maistrello et al., 2016, 2018; Mori et al., 2017) and more specifically in Sicily (e.g., Faraone et al., 2017; Mannino & Balistreri, 2018). The involvement of a large number of citizens can be a precious tool in order to monitor species presence across large areas. Exaireta spinigera is a relatively large insect (up to about 14 mm) and it is characterized by a colorful and easily distinguishable habitus (Fig. 1). It may easily attract the attention of a potential photographer and it can be identified even with a low-quality picture due to its unmistakable aspect. Significant occurrence data on Diptera, gathered from pictures taken by non-specialists and uploaded on internet, were also gathered in the case of native and even endangered species (e.g., Marcos García & Ricarte, 2013; Álvarez Fidalgo et al., 2018). The presence of E. spinigera in the Italian territory (peninsular Italy and now Sicily island) is solely known thanks to amateur entomologists and other citizens, who operated outside the framework of a focused citizen science project, but were active in biodiversity-themed internet forums and Facebook groups. In these forums and groups hundreds of thousands of relatively verifiable data are uploaded daily, mostly following a very simple but effective ‘protocol’: providing pictures of organisms along with temporal and geographic information. Such protocol is the same of platforms as iNaturalist (www.inaturalist.org). While the resulting data may be comparatively less easily available to the scientific community in the case of forums and Facebook groups, social media may attract more participants. In conclusion, a way to easily pass the data uploaded on social media and forums to large databases like GBIF (Global Biodiversity Information Facility, www.gbif.org) could be beneficial in the future. The use of social media to gather relevant data on biological and ecological issues is likely to increase in the future (e.g. Hart et al., 2018).