Hoverflies (Diptera: Syrphidae) provide an excellent opportunity to study the evolution of Batesian mimicry, where defenceless prey avoid predation by evolving to resemble defended ‘model’ species. While some hoverflies beautifully resemble their hymenopteran models, others seem to be poor mimics or are apparently non-mimetic. The reasons for this variation are still enigmatic despite decades of research. Here, we address this issue by mapping social-wasp mimicry across the phylogeny of Holarctic hoverflies. Using the ‘distance transform’ technique, we calculate an objective measure of the abdominal pattern similarity between 167 hoverfly species and a widespread putative model, the social wasp, Vespula germanica. We find that good wasp mimicry has evolved several times, and may have also been lost, leading to the presence of non-mimics deep within clades of good mimics. Body size was positively correlated with similarity to the model, supporting previous findings that smaller species are often poorer mimics. Additionally, univoltine species were less accurate wasp mimics than multivoltine and bivoltine species. Hence, variation in the accuracy of Batesian mimics may reflect variation in the opportunity for selection caused by differences in prey value or signal perception (influenced by body size) and phenology or generation time (influenced by voltinism).

Please see corresponding manuscript for all the methods for the collection and processing of data.

Dataset - Excel file uploaded 10/08/21 

The similarity of each hoverfly species to each wasp model according to the distance transform analysis. Taxa with entirely black abdomens have a similarity score of zero. Survey score is out of 10. 'Similarity category' refers to the assignment of a binary mimicry category according to the similiarity score threshold (0.74) for Vespula germanica, while 'Literature category' refers to how the accuracy of social wasp mimicry is described for each hoverfly species in previous studies. There are four potential ecological predictors for mimicry - wing length, larval feeding (the diet each hoverfly species has during its larval stage), 'voltinism' (how often each species emerges in a year (univoltine, bilvoltine and multivoltine meaning once, twice and multiple times per year respectively)) and phenology (when each species emerges in a year). The key flight periods were defined as ‘early’ (March to May), ‘mid’ (May to July) and ‘late’ (July to September).

Image_sources - Excel file uploaded 10/08/21

The source of each image used in this study. M = male; F = female. Internet sources: NS = naturespot.org.uk; iN = inaturalist.org; f = flickr.com; BG = bugguide.net; S = syrphidae.myspecies.info; D = diptera.info. A † indicates where the image was the only one of decent quality found for that species, and blank cells indicate that the information could not be found.

Species_reasoning - Excel file uploaded 10/08/21

The reasoning behind why each species was selected for this study, with information on abundance, distribution and the availability of high-quality images. Homogeneity refers to to how similar abdominal colour patterns are between individuals of the same species (intraspecific) and between species within the same genus (interspecific). References: Steven Falk - flickr.com; BugGuide.net; fauna-eu.org; Francis Gilbert pers. comms.; Van Veen, M.P., 2010. Hoverflies of Northwest Europe: identification keys to the Syrphidae. KNNV Publishing.