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Medium-sized to large (9.0-12.0 mm), non-biting
nematocerous flies. Body stout, dull black to reddish-brown,
resembling that of bibionids. Ocelli distinct; eye divided
longitudinally into two parts, with different (male) or identical
(female) size of facets, holoptic in males, dichoptic in females;
antenna compact, relatively short, with 14-17 segments. Wing
darkened, with distinctive venation: C reaching to apex of R4+5,
R1 long, R2 ending in or close to apex of R1
in C, radial sector branched proximally to r-m, M forked with a
short stem, A1 well developed but its distal part
atrophied. Haltere very long. Legs short, tibial spurs absent. The
larva lives in the very moist rotten wood of fallen tree trunks that
have lost their bark, forming a flask-shaped cavity filled with
liquid; it moves in the cavity with its respiratory siphon remaining
on the surface. The few relict species inhabit damp places in
primeval forests. Adults of the only European species, Mesaxymyia
kerteszi (Duda, 1930), are strongly stenochronous and are
therefore seldom collected.
One rare species is known to occur in Europe (de
Jong 2007); so far it has only been recorded from Ukraine and
East Slovakia. Current knowledge of the family is summarised by
Krivosheina (2000)
who has provided keys to the Palaearctic genera (both to adults and
immature stages). M. kerteszi can be identified with the keys
by Mamaev (1968)
and Martinovský and Roháček (1993).
The nomenclature used here follows that in the Fauna Europaea (de
Jong 2007).
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