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Is it possible to identify this one from photos? Should be genus Hydrophorus. Maybe H. rufibarbis or H. bipunctatus?

Found on the surface of a pool close to the ocean in Bod�, northern Norway. Size approx. 4 mm.

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Second:

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Third:

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Fourth (pale hairs on front coxa)

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I'd say Hydrophorus geminus Frey (clypeus seems to be not silvery)

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Is there any way to confirm H. geminus? I still have the fly. I have used d'Assis Fonseca's key, but it does not include this species.

Hydrophorus geminus is not known from Norway according to Fauna Europaea...(but it's known from Sweden and Finland).

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4. Wings with numerous brownish-yellow-spots in anterior half; fore femur
with 6-7 strong spines in basal part; 2.3-2.7........................nebulosus Fallén
– Wings with 2 spots on a posterior transversal vein m-cu and on M1+2 flexure..5
5. Fore femur at apex with a small lobe, excavation and bunch of setae; IV sternite
with a light spot; fore coxae with black hairs........................................6
– Fore femur at apex without an excavation and lobe ........................................7
6. Epistome mostly silvery-white, with small spot under antennae, usually two
times higher than clypeus; its maximal width usually half wider than minimal
width; acrostichal setae short; fore femur with short ventral hairs;
proepisteron with white hairs; 3.5-5.0......................................albiceps Frey
– Epistome mostly metallic-green, with weak dusting in inferior part, usually
1/3 higher than clypeus; its maximal width usually 1/4 wider than minimal
width; the acrostichal setae are longer; fore femur with longer hairs;
proepisteron mainly with black hairs; 4.2-5.4....................signifer Coquillett
7. The fore tibia are clearly squeezed and are strongly bent; legs with long hairs;
4.1-5.2................................................................................ rogenhoferi Mik
– Fore tibia cylindrical, straight ........................................................................8
8. Epistome metallic brilliant, green; fore femur with one row of strong setae in
basal part; 3.6-5.2.....................................................bipunctatus (Lehmann)
– Epistome without metal shine, or if shining, then clypeus white .....................9
9. Clypeus silvery-white .................................................................................10
– Clypeus with dark-coloured dusting.............................................................12
10. Halter with a dark spot at apex, epandrial lobe at apex almost straight; 3.5-
5.4......................................................................................... borealis Loew
– Halter yellow...............................................................................................11
11. Fore femur with long whitish anteroventral setae equal in length to diameter
of femur; clypeus silvery-white, epistome with a metallic-green spot under
antennae; 3.6-4.4 .........................................................norvegicus Ringdahl
– Fore femur without long whitish anteroventral setae in apical half; face with
whitish-grey tinge; 2.9-3.9...........................................rufibarbis Gerstäcker
12. Leg without long hairs; halter dark; 3.8-4.4..............................geminus Frey
– Midtibia with long hairs exceeding in length diameter of tibia, halter usually light with dark knob; 3.2-4.8...................................................... pilipes Frey

Grichanov, I.Ya., 2006. A checklist and keys to North European genera and species of Dolichopodidae (Diptera). - VIZR
RAAS (Plant Protection News, Supplement) 2006: 1-120.
http://www.dipter...p?cat_id=8

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Thank you for the link to the key to Dolichopodidae.

It seems more like Hydrophorus pilipes? The halters are light with a dark knob? Middle tibia have long hairs (don't know if they're long enough?).

Length from measure with USB microscope is 4,50 mm.

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Close up of middle tibia:

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A last photo showing side of body better:

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I can see only 2 setae on the scutellum. If this is the case than it is Hydrophorus oceanus Macquart.

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It has 4 setae on the scutellum? I'm not very experienced with this though :|

Photo of scutellum, hope this helps with determining.

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Grichanov has also this key online
http://www.fortunecity.com/greenfield/porton/875/SwedenHydrophorus.htm
I have found H. borealis in northern Sweden and another species without spots on the wings i can't identify and a smaller one up in the mountains.

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Thank you.

Is it a female? I've some problems figuring out which sex it is....(normally not a problem, but in some genera I think it's not so obvious).

It could be H. borealis then? I don't have much to compare with, think it's difficult only using keys to determine insects.

Attaching a photo of sternites...

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I agree with Igor:

Hydrophorus geminus Frey female

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Yes, thank you! I agree too after going through the key again.

I keyed it as a male the first time. It is a female, right?? Then it ends up as geminus (I've also found a H. borealis female and male at the same location).