Bees get a lot of good press these days, especially for their role as pollinators. And let’s face it, they deserve it! Hard working, unassuming, attractive and useful! They are almost supplanting those poster boys and girls of the insect world: butterflies!
But what about flies? Their press is a mixed bag. To some people they are dirty, disease-spreading, decomposing pests! To others, they are objects of wonder and beauty, to be appreciated and admired for the jobs they do. Overall, I think their popularity is slowly increasing as we come to realise the gamut of benefits they bring.
Most notably their role as pollinators. There are said to be 71 dipteran families containing ‘flower-visitors’ (Orford et al., 2015), regularly paying their respects to a huge number (500+) of plant species, including many cultivated species.
Nevertheless, the pollination services of flies are often underestimated it seems, especially the contributions of the non-syrphid Diptera; ‘The forgotten flies’ (Orford et al., 2015). Many flies are well adorned with bristles – such as the Muscidae and Scathophagidae – that are effective at trapping pollen (see below).
Other flies are markedly furry ! Such as the Bombyliidae, which according to one study are thought to have hairs adapted for carrying pollen. I’m not sure whether that is by accident or design (=evolution). Bee flies emerge early in the year and need to keep warm!
Flies visit flowers for the same reason as bees: for a sip of nectar and a light snack of pollen! Of course, other flies visit host plants to lay their eggs on them. (Entomologists say ‘deposit’ an egg, as if the insects were going to the bank! Stick, insert or poke an egg might be more accurate terms!😊)
Flies are second only to bees in terms of flower-visitation (Larson, 2001), and they probably were amongst the first angiosperm pollinators to have evolved, and may have played a key role in the
early radiation of flowering plants. I think flies got there before bees? Certainly, many flower-loving flies, including bee-flies, were amongst the earliest highly-specialised flower-feeding insects, according to Shaw (2014).
Of course, just because a fly visits a flower does not necessarily mean that it is a good pollinator. The bulk of the heavy-lifting in terms of pollination might still be being carried out by bees. In fact, flies are sometimes considered to be rather ineffectual pollinators (see discussion in Inouye et al., 2015), but this may be because the quality and quantity of their pollination activities has not been accurately assessed. Recent studies seem to indicate however, that they are effective pollinators in both natural and agricultural ecosystems (Inouye et al., 2015).
Inouye, D. W., Larson, B. M., Ssymank, A., & Kevan, P. G. (2015). Flies and flowers III: ecology of foraging and pollination. Journal of Pollination Ecology, 16(16), 115-133.
Larson, B. M. H., Kevan, P. G., & Inouye, D. W. (2001). Flies and flowers: taxonomic diversity of anthophiles and pollinators. The Canadian Entomologist, 133(4), 439-465.
Orford, K. A., Vaughan, I. P., & Memmott, J. (2015). The forgotten flies: the importance of non-syrphid Diptera as pollinators. Proc. R. Soc. B 282: 20142934. http://dx.doi.org/10.1098/rspb.2014.2934
Shaw, S. R. (2014). Planet of the Bugs: Evolution and the Rise of Insects. University of Chicago Press.
Ssymank, A., & Kearns, C. (2009). Flies-pollinators on two wings. Caring for Pollinators: safeguarding agrobiodiversity and wild plant diversity. Bundesamt für Naturschutz, German Federal Agency for Nature Conservation, Bonn, 39-52.
Ssymank, A., Kearns, C. A., Pape, T., & Thompson, F. C. (2008). Pollinating flies (Diptera): a major contribution to plant diversity and agricultural production. Biodiversity, 9(1-2), 86-89.
Woodcock, T. S., Larson, B. M., Kevan, P. G., Inouye, D. W., & Lunau, K. (2014). Flies and flowers II: floral attractants and rewards. Journal of Pollination Ecology, 12(8), 63-94.