Stiletto Fly (Thereva nobilitata)
The pointed abdomen of this species and its relatives have led them to be called stiletto flies. This species reassembles the group known as robber flies and shares some of their characteristics. The are rarely seen on flowers preferring to wait on leaves for passing small insects which they dart out and attack. They have a lot of hairs which protects them against struggling prey.
The larvae are found in leaf litter and are omnivorous eating both rotting vegetation and taking live prey. The adults can be seen from May to August but are most numerous later in the summer when they often form large mating swarms.
Find out more here: http://www.natureofdorset.co.uk/species_panel/Stiletto%20fly%20%5BT%20nobilitata%5D