Hydromyza livens
An elongate, dark coloured fly with very reduced head and thoracic bristles. The ocellar bristles are absent and the frontal orbitals are very short. Frons reddish, face jowls and palps yellow. Thorax and abdomen dark grey. Thorax with two brownish stripes along the lines of the very short dorsocentrals. Femora dark, but with yellow tips and tibia also dark with yellow knees and apexes. Tarsi dark, halteres and wing veins all dark. Wing length: ♂ 6.5 - 6.6 - 6.8 mm (2); ♀ 6.7 mm (1).
The larvae mine the stems and leaves of water lilies (Nuphar, Nymphaea) and Smith (1987)[1] illustrates the mines. Adults are generally found running about over the surface of lily pads. This habit makes them hard to approach. They are also quite alert and can be challenging to catch! These factors may account for the scarcity of records, although not hard to detect by searching for mines on the lily pads using binoculars.
References
Under the microscope, this species is unmistakable because of its exceptionally short head and thoracic bristles which gives it a shaved appearance. In the field, it can easily be confused with Spaziphora hydromyzina which may also be seen running over water lily pads. At least in my area, on the River Nene, the two species are often both present on the lily beds. Both species are generally grey, quite elongate in body shape and have a yellow face. Viewed at a distance through binoculars, it is not easy to resolve the bristles on the head and thorax of Spaziphora. However, with a bit of practice, they have a distinctly different jizz. Hydromyza appears quite a bulky fly and typically sits in a rather squatting position with its body appearing to be in contact with the lily pad. On the other hand Spaziphora appears more slender and remains "up on its toes" with the body held high and well clear of the lily pad.
Recorded from southern and eastern Britain and can be quite abundant in slow moving rivers and larger ditches. They are certainly widespread and abundant on water courses through the East Anglian fens and also on some rivers in the New Forest.
World distribution: Palaearctic: Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Lithuania, Netherlands, Norway, Poland, Sweden, Switzerland; Russia: northern European regions.