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Droneflies (Syrphidae: Eristalis spp. resemble honeybees (Apis mellifera) in appearance and have often been considered to be Batesian mimics. This study used a focal watch technique in order to compare the foraging behaviour of droneflies Eristalis tenax, Eristalis pertinax, Eristalis arbustorum and Eristalis nemorum) whilst they were feeding on patches of flowers with the behaviour of honeybees and other hymenopterans and dipterans. It was found that, on a range of plant species, the time droneflies spent on individual flowers and the time spent flying between them was more similar to that of honeybees than to the times of other hymenopterans and dipterans. These results suggest that dronefly behaviour has evolved to become more similar to that of honeybees and they support the hypothesis that droneflies are Batesian mimics.

SUMMARY Many hoverfly species show specific or non specific morphological resemblance to wasps (Vespula sp.) and it has been suggested that they also show similar flight behaviour. In this study we therefore compared the flight behaviour of wasps with that of four mimetic hoverflies, Sericomyia silentis, Myathropa florea, Helophilus sp. and Syrphus sp., by filming insects while they were foraging on an artificial array of flowers. Films were analysed to determine the routes taken, time spent hovering and flight speed. Of the four flies, only the non specific mimic, Syrphus, showed similar flight behaviour to the wasps; it flew more slowly, and with more roundabout routes than the other flies, hesitating before landing. These results suggest that in hoverflies there is little reason to expect strict correlation between morphological and behavioural mimicry; insects may acquire the similarities to their model more-or-less independently.

It is believed that the resemblance of many hoverflies to stinging hymenopterans is a case of Batesian mimicry, though there is little experimental evidence that it is effective in protecting them from predators. In this study the effectiveness of hoverfly mimicry was investigated for humans by presenting groups of university students and schoolchildren with a questionnaire which included pictures of stinging hymenopterans, mimetic hoverflies and dipteran controls. More people thought that the mimics would sting than either of the control flies, though fewer than those who thought that the mimics' hymenopteran models would sting. This showed that the hoverflies' mimicry worked but was not 100% effective. More people thought that the good mimics would sting than poor mimics which were black and yellow, showing that the reaction was not just due to their warning coloration. Students' identification skills were poor; only 77%, 66% and 50% were able to correctly identify wasps, bumblebees and honeybees, respectively, but even knowledgeable students were confused by mimetic hoverflies. Significantly more of the students who had been stung thought that the Hymenoptera would sting and identified Hymenoptera correctly. Students who thought a hymenopteran would sting were in turn more likely to think that its mimic would sting. This suggests that the mimicry is partly mediated by experience. However, even students who had never been stung showed the same pattern of discrimination as those who had, suggesting that information is also passed on culturally. These results suggest that mimicry is effective and might help hoverflies avoid predation by birds but, as many of the subjects said they would kill a stinging insect, this would actually increase their chances of being killed by humans.