Vol 10 Part 14. An introduction to the immature stages of British Flies ...

together. P. trivia/is Ea ton (figs 37- 38) is a common species, the larvae of which may be
seen creeping about on the surface of mud, though the mud particles trapped in the
dorsal setae may render them inconspicuous apart from the winding tracks left by
their movements. The larvae of P. trifasciata (Meigen) and P. calcilega Feuerborn are
normally thickly encrusted with lime.
The larva of Philosepedon humeralis (Meigen) (fig. 34), the only British representative
of the genus, feeds in dead snails (Vaillant, 1961; Smith & Grensted, 1963).
Only three of the 17 British species of Telmatoscopus are known in the larval stage;
they should be sought at the edges of ponds or lakes where the ground is moist and
occasionally submerged, though Withers (1986) records T. tristis Meigen and T.
advenus Eaton from tree rot-holes.
Jung (1956) keys and describes some Panimerus, Threticus and Clytocerus larvae.
The immature stages of other British genera and species remain undescribed from
native material but Vaillant (1971-1976) should be consulted for descriptions of some
and notes on the likely habitats in which to search for others (but frequently under
names differing from the British Check List).
Trichomyiinae. The larva of Trichomyia urbica Curtis, the only British species, is
found in the rotting wood of fallen trees where it makes a gallery running in the
direction of the grain (Keilin & Tate 1937). The body, unlike that of other Psychodidae,
is devoid of long setae and the head is strongly chitinized (fig. 40).
Sycoracinae. The larvae of this subfamily are associated with fast streams and waterfalls
where they live on rocks in the splash zone or near the surface. Sycorax silacea
Curtis (fig. 39), the only British representative of the subfamily, resembles a small water
louse (Asellus) and is found among mosses or rotting leaves in such situations.
An account of the British species of Psychodidae, by Mr P. Withers, is in press.
Ptychopteridae
(Figs: larva 41 , pupa 1113)
The family Ptychopteridae contains more than 60 world species in three genera. In
~ritain the family is represented by only the genus Ptychoptera with 7 species of which 6
have been described in the larval stage.
The larva (fig. 41) is very distinctive, with a long, narrow cylindrical body
terminating in a long retractile respiratory siphon. It is whitish-grey in colour,
frequently with a pair of brownish eye-spots. The respiratory system is metapneustic.
Small prolegs, each with a single hook-like spine (vh) are present on abdominal segments
1- 3. The presence of lateral and median brushes on the labrum, and of setal
brushes on the mandibles (md) and maxillae suggest a detritus feeding habit.
Ptychoptera larvae are semi-aquatic and inhabit saturated mud, or shallow muddy
pools in marshes, Sphagnum pools, or the margins of streams. Larvae of P. contaminata
(L.) prefer mud covered with water and having a high organic content; they are usually
common around farmyard pools and similar situations. P. albimana(F.)is usually found
in mud without a high organic content, e.g. open marshes, thin woodland; P. lacustris
Meigen and P. pa/udosa Meigen (and P. longicauda Tonnoir teste R.l. Vane-Wright)
occur most frequently in woodland streams, in medium or dense shade; P. scutel/aris
Meigen is restricted to acid pools with Sphagnum, often at high altitudes in upland
marshes; P. minuta Tonnoir has been found in a drainage channel around peaty fields.
Brindle (1962d, 1966) and Hansen (1981) provide keys to the known British larvae
with descriptions and ecological notes and Miall ( 1985) gives some interesting
behavioural notes.
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