This lovely fly has recently invaded Europe. Will it fly across the Channel and establish itself in the UK? Is it already here? It is spreading widely on the Continent, so perhaps it is just a matter of time before it pops up in the UK? I could find no records of it, but it is certainly one to look out for and it has some interesting behaviour!
The peacock fly (Callopistromyia annulipes) is a species of picture-winged fly in the genus Callopistromyia (Family Ulidiidae). The peacock fly belongs to a genus which contains just two species, both of which are native to the Nearctic Region (North America).
This species appears to have been introduced somehow into Europe: one female fly was found in Switzerland in 2007. Since then it seems to have spread over much of Europe. I found references to finds of it in Belgium, France, Germany, Italy, Austria, Switzerland, The Netherlands, the Czech Republic, Poland, Romania, Hungary, Slovakia and Slovenia (see references). Recently, it has been found in Western Ukraine ( Dvořák et al., 2019).
It is a saprophytic species, which means that it (its larvae) feeds on on dead and decaying matter. Its first occurrence in the Palearctic Region came from Southern Switzerland in 2007, when one female was found in a vineyard (Merz 2007).
The wings of the Peacock flies are densely patterned: almost completely filled with dark dots (see below). Callopistromyia annulipes is rather unique in that it holds its wings in a perpendicular to its body and opens and spreads them whilst shuffling back and forth at the same time (see Videos below). The wings form “striking patchworked, iridescent-fans, which are moved in an arrhythmic jerking motion as the flies periodically run to and fro” (Archer & Hosken, 2016). Both males and females do it; perhaps in a courtship which allows for mutual mate choice.
There are lots of other picture wing flies (Diptera: Pallopteridae, Platystomatidae & Ulidiidae) in the UK, including about 20 species in the family Ulidiidae (wing-waving flies), but none that looks, or behaves like the Peacock fly.
The Peacock fly is an alien invasive species in Europe. On the one hand, with its pretty looks and interesting behaviour, it might be seen as a welcome addition to our wing-waving dipteran fauna? On the other hand, we do not know what impact it might have, perhaps displacing some native species from a similar niche. This species is almost certainly established, i.e. here to stay in Europe, given that it has spread widely, seems to find the climate suitable, and its larvae can live on many different tree species (Smit & Hamers, 2011).
Certainly one to look out for in the UK.
References
Archer, C. R., & Hosken, D. J. (2016). Peacock flies. Current Biology, 26(21), R1124-R1126.
Dvořák, L. (2017). The first records of Callopistromyia annulipes (MACQUART, 1855)(Diptera: Ulidiidae) from the Czech Republic. Acta Musei Silesiae, Scientiae Naturales, 66(2), 111-112.
Dvořák et al. (2017). New records of Callopistromyia annulipes (Diptera: Ulidiidae) from Slovakia. ACTA UNIVERSITATIS PREŠOVIENSIS, 9(2), 18.
Dvořák, L., Haenni, J. P., Dvořáková, K., Kameneva, E. P., Mariychuk, R., Manko, P., … & Korneyev, V. A. (2019). Some insects from beer traps in Westernmost Ukraine. Ukrainska Entomofaunistyka, 10(2), 1-6.
Korneyev, V. A., Dvořák, L., & Kameneva, E. P. (2014). New Records of Callopistromyia annulipes Macquart (Diptera: Ulidiidae: Otitinae: Myennidini) in Europe. Ukrainska Entomofaunistyka, 5(10).
Kameneva, E. P., & Pekarsky, O. (2016). First record of Nearctic invader, the peacock fly Callopistromyia annulipes MACQUART (Diptera: Ulidiidae: Otitinae: Myennidini) from Hungary. Ukrainska Entomofaunistyka, 7(4), 38.
Merz, B. (2007). Callopistromyia annulipes (Macquart, 1855), a Nearctic species of Ulidiidae (Diptera), new for the Palaearctic Region. Studia dipterologica, 14(1), 161-165.
KLASA, A., & JAŁOSZYŃSKI, P. (2018). DIPTERON. Bulletin of the Dipterological Section of the Polish Entomological Society, 34, 22-29.
Pintilioaie, A. M., & Manci, C. O. (2020). First record of the peacock fly Callopistromyia annulipes (Diptera: Ulidiidae) in Romania. Travaux du Muséum National d’Histoire Naturelle “Grigore Antipa”, 63, 87.
RAVOET, J., & FARINELLE, C. (2017). The peacock fly Callopistromyia annulipes (Macquart, 1855): a long expected new addition to the Belgian fauna (Diptera: Ulidiidae). Bulletin de la Société royale belge d’Entomologie, 153, 121-122.
Roland, E., Iakushenko, D., & Gabryś, G. New record of the alien Nearctic species Callopistromyia annulipes (Macquart, 1885)(Diptera: Ulidiidae) from Poland.
Rolke, D. (2017). Die invasive Pfauenfliege Callopistromyia annulipes (MACQUART, 1855)(Diptera, Ulidiidae)–neu für die Fauna Brandenburgs. Märkische Entomologische Nachrichten, 19(1), 109-111.
Smit, JT, & Belgers, D. (2011). Interesting sightings of drill and beautiful flies in the Netherlands (Diptera: Tephritidae, Ulidiidae). Dutch Faunistic Notices , 36 , 29-47.
Smit, JT, & Hamers, B. (2011). The invasive North American peacock fly Callopistromyia annulipes new to the Netherlands (Diptera: Ulidiidae). Dutch faunistic notices , 36 , 23-27.
Videos and Links
Ray Cannon's nature notes 
interesting stuff on the peacock fly – a beauty – Ray, many thanks