The large umbellate flower-heads of hogweed (photo 1) are a favourite foraging area in high summer for insects seeking pollen and nectar, particularly flies and soldier beetles (photo 2).
Gwen was scanning some flower-heads in her garden at Torbreck (NC0824) on 9th July, when she noticed a really striking fly. It was about 10mm long, with red eyes and curved wings streaked in blue (photo 3).
Since about 7100 species of flies are known to occur in the British Isles, putting a name to them can be challenging. However, Britain’s Insects, Paul Brock’s encyclopaedic and copiously-illustrated book in the WildGuides series (2021), features a range of the more conspicuous species.
Gwen was looking at the section on the Calliphoridae (bluebottles and their allies), which seemed a good place to start. Just over the page were pictured four examples of another family, the Tachinidae (parasitic flies) including, happily, the one in question, a male blue-winged tachinid Phasia hemiptera.
Tachinids are quite a large family with some 267 British species, all parasitoids with larvae that develop inside other insects, although the adults are pollen feeders. This species preys on large shieldbugs, such as the forest bug or red-legged bug Pentatoma rufipes (photo 4, taken at Torbreck in 2020), which occurs locally on trees such as alder, hazel and oak.
NBN has no Scottish records of the blue-winged tachinid north of Lael, near Ullapool, and Spinningdale, over in east Sutherland, so it is ‘new’ to Assynt and, so far as we know, the northernmost record in the British Isles.
Gwen Richards and Ian M. Evans