The mimicry of honeybees (Apis mellifera) by droneflies

(Eristalis spp.) has been fooling humans for thousands of years (Atkins, 1948). The important question in considering whether it is a true case of Batesian mimicry, however, is whether it fools their predators, which are thought to be birds. Eristalis spp. are not considered to be the best visual mimics of honeybees; other British hoverflies such as Mallota cimbiciformis (Fallén), Criorhina asilica (Fallén) and Brachypalpus laphriformis (Fallén) are thought to be better (Stubbs and Falk, 1983; Howarth et al., 2000), while Morgan and Heinrich (1987) even categorise Eristalis spp. as nonmimetic. Previous work, however, found that, on a range of flowers throughout the season, the foraging behaviour of Eristalis spp. was more similar to that of Apis mellifera than to that of other more closely related flies (Golding and Edmunds, 2000), and this was confirmed by the general impression gained from watching them in the field. There were similarities between droneflies and honeybees in the times spent sitting on flowers and in the times flying between flowers, suggesting that droneflies may be behavioural mimics. This study investigates this possible flight mimicry further. Studies of flight in hoverflies have been concerned mainly with aerodynamics (Ellington, 1984), with flight mechanisms, wing design and kinematics (Ennos, 1987, 1988, 1989) and with other behavioural aspects, such as the mechanisms by which hoverflies compute interception courses (Collett and Land, 1975) and manage to return to exactly the same spot (Collett and Land, 1978). Flight mimicry has not been studied specifically. Mimetic resemblance of flying insects has, however, been observed in flower-visiting beetles of the genus Acmaeodera, which look very much like hymenopterans in flight (Silberglied and Eisner, 1969). Other examples include the mimicry between Lebia vittata (Carabidae) and Disonycha scapulari (Chrysomelidae), in which the chrysomelid flea beetle has evolved an effective escape mechanism so that a potential predator gets zero reward (Lindroth, 1971). Hespenheide (1973) described a case of Müllerian mimicry in which agile flies and their beetle models act in a similar way. Examples such as these have, however, been criticised by Brower (1995), who maintains that evidence for unpalatability of the models is often anecdotal. Hoverflies regularly appear in the diet of birds, e.g. swallows (Hirundo rustica) (Kozena, 1979), swifts (Apus apus) (Lack, 1956), house martins (Delichon urbica) (Bryant, 1973), wagtails (Motacilla spp.) (Davies, 1977), flycatchers (Ficedula spp.) (Bures, 1995), magpies (Pica pica) and tree sparrows (Passer montanus) (Kristin, 1986), and are therefore clearly palatable. Hoverflies have been referred to anecdotally as having bee-like flight (Wickler, 1968), bumblebee-like flight (Howarth, 1998) and 139 The Journal of Experimental Biology 204, 139–145 (2001) Printed in Great Britain © The Company of Biologists Limited 2001 JEB3109