Flies with Thighs

Flies with Thighs
Syritta pipiens

Grubbing about on the shingle recently looking for rare spiders I came across this hoverfly with swollen femora near the Mary Stanford lifeboat House. This is Syritta pipiens, a tiny, narrowly-built species which is a very common in the UK and is a frequent visitor to gardens. It can be found on a wide range of flowers, feeding on either nectar or pollen, and can be an important pollinator for certain species (e.g. marsh helleborine). It is a superb flier, even for a hoverfly, and is able to remain virtually stationary in mid-air, compensating almost perfectly for wind gusts and other disturbances. The highly territorial males in particular often use this skill to good effect either when facing off with each other or when zeroing in on potential mates in flight.  One member of the public, obviously mishearing the name of this species on a walk, insisted on referring to it as Scritti polliti for the remainder of the event!

RxMerodon equestris 07a

Two other ‘fat-thighed’ hoverflies are on the wing at the moment, Merodon equestris and Tropidia scita. Merodon (above) is fairly common and widespread in a range of habitats in the UK, while Tropidia (below is somewhat local and is largely found in coastal districts in the south-east.

Rxtropidia

In terms of larval habitat, both Tropidia and Merodon are associated with plants. Tropidia is associated with reedmace where the larvae develop between the leaf sheaths, while Merodon larvae develop in various bulbs where they can constitute something of a pest (English names for this species include Greater Bulb Fly and Narcissus Bulb Fly). In contrast Syritta larvae breed in compost and manure and similar rotting organic material (including human cadavers apparently!). In common with most other hoverflies these three species mimic various hymenoptera, with Tropidia and Syritta resembling wasps and Merodon giving a fairly good impression of a bumblebee, with different colour forms looking like various different species. This mimicry by a harmless species of a one which has the potential to inflict a painful sting on a would-be predator (called Batesian mimicry) provides the hoverfly with some degree of protection. 

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