THE HOVERFLIES OF SOUTH-WEST ENGLAND – AN OVERVIEW
(DIPTERA: SYRPHIDAE)
By Leon Truscott
Approximately 180 hoverfly species have been recorded in the South-west. This
compares with about 270 on the national list. Taxonomic revision is continuously
taking place and a number of new species have recently been split from previous
taxa, so these numbers are rather variable at the moment.
The standard reference is Stubbs A. & Falk S. (2000) British Hoverflies BENHS.
Also available is Gilbert F. & Falk S. (1993) Naturalists' Handbook 5 - Hoverflies
Richmond Publishing Co. Ltd, which describes forty-two of the more common
species and contains useful keys, illustrations and notes.
Most hoverflies are fairly easily recorded or studied since they (the adults, at least)
can be found in almost any habitat, ranging from the coast to the moors. Although
some species are rather local to breeding sites, many are very widespread and can
be found almost anywhere plants are in flower, such as meadows, hedgerows and
gardens. Breeding requirements for most species could broadly be described as
woodland or wetland and in the South-west the most productive sites seem to be
wet meadows and along rides or edges of damp woodland.
A few species hibernate as adults, so hoverflies can be seen in any month of the
year, although April to September is the optimum period. They range in
appearance from tiny black flies less than 5mm in length to those which could be
mistaken for large wasps or even bumble-bees and are most often to be found
nectaring at flowers or at rest in the sun. Many, but not all, can be identified in the
field, usually but not necessarily with the aid of a hand lens. Some of the smaller
species can only be separated by examination under the microscope. Records for
the latter, should they be uncommon species, would probably only be accepted by
the national recording scheme if voucher specimens were available. Voucher
specimens are also useful for those species whose taxonomic status is under
discussion.
Early stages (eggs, larvae, pupae) are less well known by most enthusiasts and, in
general, the vast majority of records held are of adults. However, in recent years,
much work has been done on life-histories and understanding of the latter is
increasing all the time. In very general terms, there are five different life-cycle
types, based on larval feeding requirements. These are: 1. Carnivorous - feeding on
aphids; 2. Plant feeders - some species have specific food-plants; 3. Underwater
feeders – feeding on matter from a variety of water-bodies, often polluted ones; 4.
Rotting matter – from dung-feeders, through compost-feeders to those which feed
on rotting wood; 5. Scavengers: a few species feed on detritus in bees’ or wasps’
nests.
1.
Common species
There are about 80 species thought to be common in most of Britain. Almost all of
these occur commonly in the south-west. The most well known being members of
the Eristalis genus, especially E.tenax and E.pertinax. These ubiquitous hive-bee
mimics are particularly common in late summer. Perhaps equally familiar is
Episyrphus balteatus. In some years, this species is abundant, as numbers can be
boosted by migrants from mid-summer onwards.
Episyrphus balteatus
2.
Eristalis pertinax
Eristalis tenax
South-western specialists
The distribution of a number of species, although not exclusively south-western,
show a distinct bias to this region. I have picked seven examples:
a) Arctophila superbiens.
A “northern and western”
species, mainly of Wales,
Scotland and northern England.
Most records for southern
England are from Cornwall,
Devon and Dorset.
b) Callicera aurata. A rare species of central southern England. It has been
recorded from Devon and Cornwall in recent years.
c) Chrysotoxum elegans. A
scarce species of southern
England & Wales. Although
there are a few records from
woodland and scrub from
south-east England, its
strongholds are south-western
coasts.
d) Eristalinus aeneus. A coastal species, mainly of the southern half of
Britain, which can be found all round the south-western coast.
e) Eristalis cryptarum. This is very much a south-western, indeed an
exclusively Devonian species! There are old records from Cornwall,
Devon, Dorset and Hampshire, but there were none since the 1960s until
1993, when it was re-discovered on Dartmoor. It has since been found in
several Dartmoor locations.
f) Eumerus sabulonum. Another coastal species. Nearly all records are from
the coasts of west Wales and Devon & Cornwall.
g) Microdon myrmicae. A scarce species of some southern and western
districts, usually on wet heath. The larvae feed in ants’ nests on eggs and
grubs.
3.
Southern species scarce in the South-west
Some species, although frequent in southern England, are scarce in the south-west,
even though habitat requirements appear to be met. Either the latter is not the case,
or they are simply under-recorded. The following five are worth looking out for:
a)
Chalcosyrphus nemorum.
A woodland species I have found
almost annually in low numbers.
b)
Chrysotoxum cautum.
A species of grassland
& hedgerows. Fairly
common in most of
southern England, but
strangely local in the
south-west, especially
Devon. Seems to
prefer high hedgerows
in Cornwall.
c)
Criorhina floccosa. A woodland species, and, although scarce, records
are very widespread, but few are from the south-west.
d)
Didea fasciata. Like the
previous fly, a scarce, but
widespread woodland species.
Records from the south-west are
few.
e)
4.
Volucella inflata. Another
woodland species. Records
are mainly concentrated
around central southern
England, but there are a few
recent records from Devon
and Cornwall.
Scarce, but increasing species
Some species have extended their range in recent years. The classic example is
Volucella zonaria. Britain’s largest hoverfly, it became established in the
London area in the 1940s and has gradually spread westwards, reaching Devon
and Cornwall in the 1990s. Scaeva selenitica and Xanthandrus comtus are two
species whose records have increased in recent years, especially on the coast,
often in late summer, suggesting migration.
Scaeva selenitica
Volucella zonaria
Xanthandrus comtus
Of course, the distribution picture for hoverflies in general is far from
complete, and the national database is being continuously updated.
Records should be sent to the National Hoverfly Recording Scheme. The
organisers are Dr Stuart Ball, 255 Eastfield Road, Peterborough, PE1 4BH and
Mr Roger Morris, 7 Vine Street, Stamford, Lincs PE9 1QE.
Leon Truscott
59 Cremyll Road, Torpoint, Cornwall PL11 2DZ
Leon.truscott@btinternet.com