Article Hoverflies: the garden mimics. Edmunds, Malcolm Available at http://clok.uclan.ac.uk/1620/ Edmunds, Malcolm (2008) Hoverflies: the garden mimics. Biologist, 55 (4). pp. 202-207. ISSN 0006-3347 It is advisable to refer to the publisher’s version if you intend to cite from the work. For more information about UCLan’s research in this area go to http://www.uclan.ac.uk/researchgroups/ and search for <name of research Group>. For information about Research generally at UCLan please go to http://www.uclan.ac.uk/research/ All outputs in CLoK are protected by Intellectual Property Rights law, including Copyright law. Copyright, IPR and Moral Rights for the works on this site are retained by the individual authors and/or other copyright owners. Terms and conditions for use of this material are defined in the policies page. CLoK Central Lancashire online Knowledge www.clok.uclan.ac.uk Hoverflies: the garden mimics Mimicry offers protection from predators by convincing them that their target is not a juicy morsel after all. it happens in our backgardens too and the hoverfly is an expert at it. Malcolm overflies are probably the best the mimic for the model and do not attack Edmunds known members of tbe insect or- it (Edmunds, 1974). Mimicry is far more Hder Diptera after houseflies, blue widespread in the tropics than in temperate bottles and mosquitoes, but unlike these lands, but we have some of the most superb insects they are almost universally liked examples of mimicry in Britain, among the by the general public. They are popular hoverflies. because of their bright colours and darting Apparent Batesian mimics occur in every flight, interspersed with hovering around garden throughout the summer months, garden flowers. Many of these brightly including the droneflies Eristalis tenax, E. coloured hoverflies look like bees or wasps pertinax and E. arbustorum all of which - and they use this similarity to protect resemble honeybees (Apis mellifera) (Fig- themselves. ure 1), the black and yellow boverflies Batesian mimicry is where a palatable Syrphus ribesii and S. vitripennis which Title image: A form of Merodon equestris animal (the mimic) gains protection from resemble social wasps {Vespula vulgaris mimicking Bombus resembling a noxious animal (the model) so and related species) (Figure 2), and the pascuorum that predators are deceived into mistaking furry black and yellow and white hover- 202 Biologist I Volume 55 Number 4, November 2008 Hoverflies I IOB Figure 1. Eristaiine hoverfties, from ieft to right: Eristalis ßeriinax, Eristalis arbustorum (both honeybee mimics), Heiophilus pendulus (a wasp mimic) and Eristaiis intricarius (bumbiebee mimic). These hoverflies are cioseiy reiated in the subfamiiy Eristaiinae and have a iooped vein distally on the wing which is absent from many other hoverfiies. flies Merodon equestris and Eristalis intri- make predictions on the assumption that carius (Figures 3 and 1) which resemble hoverflies are Batesian mimics and then bumblebees. But do they actually derive test these predictions. protection against birds because of their similarity to hymenopterans or are they Ecology and Batesian mimicry coloured like their respective models for In 1994 Brigitte Howarth surveyed three reasons unrelated to mimicry? areas of semi-natural ancient woodland in Although colour is important in many Lancashire and Cumbria each week from insects for defence against predators, it can April until October, recording all hover- also be important in thermo-regulation, flies and hymenopterans seen on standard male-male competition and courtship. In walks. Some were identified to species, oth- hoverflies the abundance of species that ers to a group of similarly coloured species. appear to mimic hymenopterans suggests The five common bee and wasp groups were very strongly that in these species colour honeybees, social wasps, black and yellow must have some defensive value. Seventy bumblebees {Bombus terrestris, B. lucorum years ago Mostler (1935) showed that sev- and B. hortoi'um), black, yellow and rusty- eral species of hirds will eat hoverflies hut red bumblebees (Bombus pratorum) and quickly leam to avoid attacking wasps, brown bumblebees {B. pascuorum). and they then also refuse to attack the Her first prediction was that if hoverflies wasp-like hoverflies Serieomyia and Chry- are Batesian mimics, then they should sotoxum (Figure 2). In the same way he occur at the same season as the models also showed that droneflies are protected and be rarer than the models. If they oc- by their resemblance to honeybees while cur at other times or are commoner than Volucella bombylans is protected by its the models, then birds are likely to catch similarity to bumblebees (Figure 3). a mimic and find it tasty before they have These experiments were in an aviary, caught a model and learned to avoid in- though, and obtaining proof that any hov- sects with that colour pattern; in such erfly really does gain protection through cases, mimicry is unlikely to evolve. Batesian mimicry in the field is not at all All of the hoverflies that resembled easy: one would need to show that birds bumblebees (including Volucella bomby- (or otber predators) kill fewer flies that lans, Criorhina berberina and Arctophila mimic wasps than similar flies that do not superbiens., Figure 3) were indeed much mimic wasps. rarer than their models, so too were the One way of tackling this problem is to wasp-like Serieomyia silentis and Chiy- Figure 2. Wasp-like hoverfiies, from ieft to right: Syrphus ribesii, Episyrphus batteatus. the marmaiade fly (these are both 'poor' mimics), Serieomyia silentis and Chrysotoxum festtvum (two 'good' mimics with more wasp-iike patterns and, in Chrysotoxum, conspicuous antennae). Volume 55 Number 4, November 2008 I Biologist 203 IOB I Hoverflies Figure 3. Bumblebee mimics, from top left to bottom rigtit: Criorhina berberina typical form mimicking Bombus terrestris, Criorhina berberina oxyacantbae mimicking Bombus pascuorum, a form of Merodon equestris mimicking Bombus pascuorum, Che'ilosia iiiustrata mimicking Bombus pratorum. Voiuceiia bombylans typica mimicking Sombus lapidarius and Voiuceita bombylans piumata mimicking Somûus terrestris. sotoxum spp. (Howarth and Edmunds, mimicry may be breaking down. However, 2000). These are all insects that hear a many years ago Jane Brower (1960), using very close resemhlance to their models so mealworm prey with caged birds, showed can he called 'good mimics'. But the yellow that if a model is sufficiently nasty then and black Hdophilus spp. (Figure 1) and mimics can still gain some protection even Syrphus spp. and the orange and hlack when they outnumber the model by nine Episyrphus baiteatus (Figure 2) were all to one. So do superabundant droneflies and much more numerous than their supposed wasp-like hoverflies indeed benefit from wasp models, as also were droneflies com- Batesian mimicry? pared with their honeybee models. To the In her survey work Brigitte Howarth human eye many of these abundant hov- made a second prediction: that if mimicry erflies (particularly the wasp-like ones) occurs then hoverfly numbers should be are not as similar to their supposed models positively related to numbers of their sup- as are the rarer 'good mimics' so they can posed models. If there is no mimicry then be referred to as 'poor mimics'. there should be no necessary relationship Dittrich et al. (1993) trained pigeons to between dronefly and honeybee numbers. avoid pictures of wasps but to peck at flies, In collaboration with Francis Gilbert this and found that the yellow and black hov- was tested by means of a General Linear erflies that looked like wasps were better Model (GLM) to explore how dronefly num- protected than black flies. But pigeons at- bers were related to a variety of environ- tacked the orange and black Episyrphus mental factors (see Table 1). As one would baiteatus the least, even though to our eyes expect, dronefly numbers were significantly it is a 'poor mimic'. This work suggests that affected by time of year, habitat (woodland, these apparently poor mimics may still be scrub or pasture), temperature and other protected by Batesian mimicry because hoverflies (more droneflies were present on birds perceive them differently from hu- warm days and when other flies were also mans. common). However, there was also a sig- More recently Azmeh et al (1998) found nificant positive relationship to numhers that these very abundant but poorly mi- of honeybees but a negative relationship to metic wasp-like hoverflies are not so com- numhers of other hymenopterans (Howarth mon in ancient forests of Poland and Rus- et al, 2004). This is precisely what one sia as they are in secondary forests, fields would expect if droneflies are indeed mim- and gardens, so it is possible that they have icking honeybees. There were similar posi- increased due to human-induced changes tive relationships between numbers of the to the environment. If true, then the pro- smaller honeybee mimic Eristalis arbusto- tection they receive may be minimal and rum and honeybee numbers, and between 204 Biologist I Volume 55 Number 4, November 2008 Hoverflies I IOB both Syrphus spp. and Episyrphus baitea- Table 1. Results of General Linear Model showing that there are significant relationships tus numbers and social wasp numbers. (déviances) between dronefly numbers (Eristaiis ienax & £. pertinax) and all six variables, All of these hoverflies are often more and that for three of the four covariates the relationship is positive. Thus there are more droneflies when it is warm, when there are more honeybees and when there are more numerous than their models, hut it is diffi- hoverflies present. The six variables listed account for 65% of the variance in dronefly cult to think of a good reason why this cor- numbers, relation should occur unless the hoverflies are indeed gaining protection through Ba- Variable Deviance d.f.