Siphona geniculata
The genus Siphona is comprised of a number of small, grey and very similar species. It is very hard indeed to name them from just a photograph. Siphona geniculata is extremely useful in one's garden, because it prefers the larvae of Crane Flies, a major pest in lawns. One Crane Fly larva, better known as leatherjacket, may contain dozens of Siphona geniculata larvae! Of all Siphona species, Siphona geniculata is the most common by far. The adult flies may suck nectar from flowers, but they also hunt for smaller insects, such as small flies and cicadas.