The first account of threatened British Diptera was included
in Shirt (1987). This listed 827 Diptera, 270
as Endangered, 226 as
Vulnerable, 328 as Rare and 3 as Appendix (extinct). Data sheets
were included for 82 species (35 Endangered, and 47 Vulnerable), of
which 4 were Nematocera in families treated in this volume
(
Dasyhelea lithotelmatica (now
Dasyhelea
saxicola),
Asindulum nigrum,
Neoempheria
lineola and
Sciophila ochracea) and 3 were
Aschiza (
Callomyia elegans,
Nephrocerus
scutellatus and
Cephalops perspicuus). This was
followed by the publication of
A review of the scarce and
threatened flies of Great Britain(Part 1)
(Falk 1991). This presented species accounts of threatened species
from the better-known families of British Diptera, together with a
list of all British flies provisionally assigned to Red Data Book
and Nationally Notable (now termed Lower Risk (Nationally Scarce))
categories.
The present volume deals with those Nematocera
and Aschiza which were listed but not provided with Data Sheets by
Falk (1991). Thus members of the following families are included:
Mycetophilidae sensu lato (now five families:
Bolitophilidae, Ditomyiidae, Diadocidiidae, Keroplatidae,
Mycetophilidae sensu stricto), Trichoceridae, Mycetobiidae
(sometimes included in Anisopodidae), Ptychopteridae, Dixidae,
Culicidae, Thaumaleidae, Ceratopogonidae, Platypezidae, Phoridae,
Lonchopteridae and Pipunculidae; the Atelestidae, included within
the Platypezidae by Falk (1991) but now regarded as a family of
Empidoidea are dealt with by Falk & Crossley (2005). Thus
sixteen currently recognised families, comprising about 1226
British Isles species, are considered here. Two of these families,
Ceratopogonidae (161 species) and Phoridae (329 species) are
insufficiently known for a full assessment to be attempted and Falk
(1991) listed only one and ten species (here increased to 22)
respectively in these families. In the remaining families Falk
listed 296 species or 40% of the presently known British species of
these families. The remaining families of Diptera apart from
Nematocera and Aschiza that were not dealt with by Falk (1991) are
reviewed in three further parts within the JNCC Species Status
Review series.
Most members of the Chaoboridae and Bibionidae
would not merit inclusion and as these families were not considered
by Falk (1991) it has not been practicable to gather data on those
few species which might be worthy of inclusion. The Anisopodidae is
now restricted to the genus Sylvicola with four
species, only one of which might merit inclusion but it has not
been feasible to consider it. The Opetiidae includes a single
species, formerly included in the Platypezidae, which is generally
common and this family is therefore excluded. The families
Sciaridae, Cecidomyiidae, Psychodidae, Scatopsidae, Simuliidae and
Chironomidae were also not considered by Falk (1991) because of
insufficient knowledge of the British distribution of their species
and it has not been practicable to include any members of these
families here. Rotheray et al. (2001) recommended high
status (RDB 1) for Ectaetia christii Rotheray &
Horsfield (Scatopsidae), because of its association with sap of
Aspen Populus tremula at two sites in Scotland and
this should be considered if future evaluation of this family
becomes practicable.
The state of knowledge of the families dealt with
here is very variable. There are national Recording Schemes for the
five families of fungus gnats (Bolitophilidae, Ditomyiidae,
Diadocidiidae, Keroplatidae and Mycetophilidae), Dixidae, Culicidae
and Lonchopteridae and an increasing amount of data is becoming
available for these families. The small families Trichoceridae and
Ptychopteridae (formerly also the Mycetobiidae and Anisopodidae)
are included in the "Crane Fly Recording Scheme". There is now a
substantial amount of data relating to the "fungus gnats"
(Mycetophilidae sensu lato) due to increased recording
effort in recent years and this has facilitated the assessment of
the status of species. I have also been accumulating data on
Platypezidae for many years and their distribution is becoming
better known. The Pipunculidae have received less attention than
most of these other groups and it was necessary to devote more time
to checking data against collections and consultation with
specialists in order to arrive at more reliable assessments of
their status.