One of the joys of having a patch of wildlife garden, even if it is small like ours, is sitting in the sun and watching the species that visit it. Often they are familiar - our pond attracts damselflies and dragoflies, and we try to include a wide range of pollinator-friendly plants for bees and hoverflies, but sometimes something a little different appears. In this case a little flicker of movement caught my eye and I looked closer to see two small flies waving their wings at each other. The wings had dark patterns of blotches and lines and I recognised them as being in the family Tephritidae. This family has no common name as such, but they are sometimes considered to be 'fruit flies' in the broad sense, and are also included in the informal grouping known as 'picture-winged flies'. A little more research in Smit (2010) and White (1988) confirmed the species as Tephritis neesii, which is common on Leucanthemum (e.g. ox-eye daisies as here) in southern England, where I live. So, nothing unusual as such, but I'd not seen it before; I did wonder if the 'dance' was a form of competition between males, but it is actually a male-female mating display.
Pair of Tephritis neesii during their mating dance.
It also turns out that in some tephritids, the form of the dance can indicate the genus of the fly - Tephritis such as these hold their wings flat and open/close them alternately; Urophora open/close them simultaneously while rocking from side to side; Chaetorella hold their wings sideways with the edge pointing up, then shake them. Males do fight, but it is less elegant - there was a third fly just out of shot that buzzed one of the pair later on. Though my photo shows the wing pattern quite clearly (it's the same in males and females), a video shows the dance itself, so here's one that's been kindly posted on YouTube:
References
Smit, J.T. (2010). De Nederlandse boorvliegen (Tephritidae). Entomologische Tabellen. Supplement bij Nederlandse Faunistische Mededelingen, 5: 1–159. [In Dutch]
White, I.M. (1988). Tephritid flies. Diptera: Tephritidae. Handbooks for the Identification of British Insects10(5a): 1–134.
