Slugs Count: Assessing citizen scientist engagement and development, and the accuracy of their identifications

How accurately can citizen science participants identify species, and can the information they provide be used to calculate accurate estimates of species richness, abundance and diversity measures? In this paper, we address these questions using data from a citizen science project assessing slug species diversity in gardens. Sixty participants were selected from over 2700 applicants across Britain to sample their gardens regularly for slugs following a standardised method. All slugs collected during the 30‐min search were posted to the lead investigator for verification throughout the 12‐month project. The resulting data were analysed to explore how accurate participants were in identifying slugs and whether this improved over the study period. Prior experience in slug identification was evaluated as a predictor of accuracy. Participants overestimated slug abundance and species richness, which led to overestimates in species diversity indices, illustrating the importance of verification in citizen science projects involving identification. Accuracy of slug identifications increased significantly over time in quantitative analysis of ecological data. However, self‐defined prior experience of identifying slugs before participation was not a good predictor of participant accuracy. Participants reported perceived improvement in slug identification skills to an evaluation survey after the project. However, confidence in identifying and explaining identification of slugs was lower than confidence in understanding and explaining other new science topics. This citizen science approach, including expert verification of physical specimens, illustrates how this method can be used successfully to provide accurate data on species' abundance and richness, alongside improving identification skills among the public for an understudied taxon. Continued engagement and feedback for participants is key in retaining citizen science participation in a project of this type, particularly if the taxon is challenging to identify correctly to species. Read the free Plain Language Summary for this article on the Journal blog.