Phronia larvae underneath rotten logs:

In fall, I regularly find these 2 to 3 mm long animals underneath rotting logs and fallen branches in mixed woods. As far as I can see they have no legs, but a distinct sclerotised head with two "eyes", which are in fact spiracles I was told, and a kind of snout. These absolutely weird, slug-like creatures cover their backs with a greyish-green mixture of slime and mud. I had no idea what they could be but supposed they were probably dipterous larvae. After asking the TAXACOM list and the German Arbeitskreis Diptera (http://www.ak-diptera.de/) my problem was quickly solved: these are larvae of the fungus gnat genus Phronia (Mycetophilidae). Below are some images:

Illustration of Phronia larva from Plachter, 1979. Many thanks to Uwe Kallweit for this illustration.

Many thanks for solving my problem to all TAXACOM members that replied, and especially to Don Colless and Ray Gagné, as well as to Arbeitskreis Diptera members Uwe Kallweit, Eberhard Plassmann, Horst Bathon and Frank Menzel.

Some literature:

Brauns, Adolf (1954) Terricole Dipterenlarven. Musterschmidt Verlag, Göttingen/Frankfurt/Berlin. see Fig. 23

Plachter, H. (1979) Zur Kenntnis der Präimaginalstadien der Pilzmücken (Diptera, Mycetophiloidea) - Teil II: Eidonomie der Larven.- Zool. Jb. Anat. 101: 271-392.

Plassmann, E. (1977) Revision de europäischen Arten der Pilzmückengattung Phronia (Diptera: Mycetophilidae). 40 pp.

Steenberg, C.M. (1943) Entomol. Medd. 23: 337ff.

Smith, K.G.V. (1989) An introduction to the immature stages of British flies. Royal Entomological Society of London (Handbooks for the Identification of British Insects, Vol. 10, Part 14). - see Figs. 83-84 and 89-91; short discription on page 49.

Photographs: Jan Bosselaers

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