2. English hoverflies not allocated to Priority Habitats:-
That 28 species have not been allocated or do not readily fit with BAP Priority Habitats in England may be of some concern.
3. Priority Habitats in Wales. Scotland and Northern Ireland.
a) Native Pine Woodland. This habitat supports some hoverflies confined to this habitat, and a few others that are rare outside Scotland..
Blera fallax SAP*, RDB1 saprophagous; Scotland
Callicera rufa RDB3 saprophagous; Scotland
Chamaesyrphus caledonica RDB1 biology unknown; Scotland
C. scaevoides RDB3 biology unknown; Scotland
Melangyna ericarum RDB3 aphidophagous
Metasyrphus nielseni N aphidophagous
SAP status should be considered for Chamaesyrphus caledonica. b) Mature aspen woods (classified within Native Pine Woodland).
Hammerschmidtia ferruginea SAP*,RDB1 saprophagous; Scotland only c) Mountains.
Cheilosia sahlbergi RDB2 phytophagous; Scotland only
Melanostoma dubium N aphidophagous?
Platycheirus melanopsis RDB3 aphidophagous d) Machair.
Cheilosia ahenea RDBK phytophagous This hoverfly may need consideration for SAP status.
e) Northern
Helophilus groenlandicus RDB2 aquatic This hoverfly may need consideration for SAP status.
In Wales and Northern Ireland there are no species that are country specific.
However, in Eire there are a few species not recorded from the UK.
MONITORING
Hoverflies are ideal for monitoring. A good number of species are readily identifiable sitting at flowers, without recourse to capture. For those people willing to also undertake the identification of the less distinctive ones, this is a manageable group. Remember, monitoring is worthwhile even if only just for those species you like to watch.
So why monitor? Hoverflies breed in a great range of situations, so their well-being, or decline, is a good indicator of environmental quality.
1. It is important to know whether the fauna of a site is thriving or declining, and why. This applies especially if a site is being managed for conservation purposes (is the management plan, time and effort producing the desired results?). If a site is not being managed, is intervention necessary and how urgently?
2. Some hoverflies are rapidly changing abundance and distribution, possibly related to climatic warming. Good examples are Volucella inanis and V. zonaria, two of our biggest and most spectacular wasp-mimicking hoverflies - and one of their favourite places is gardens.
3. Some hoverflies are migrants, but we know little about their pattern of advance across Britain. Such hoverflies as Scaeva pyrastri (a large species with white bars on the abdomen), or Episyrphus balteatus (the marmalade hoverfly - abdomen patterned like streaky marmalade) are easy to recognise. The later species is resident in the south of England, but in most summers there is an enormous boost in numbers nation wide. If enough people were monitoring their garden, or somewhere else nearby, we could track the dates of appearance or sudden explosion in numbers, and see the national picture in understanding the phenomenon of migration in these insects.
4. In a garden or countryside site, it is possible to adopt a standard route for counting the numbers of each species as you go round (as in Butterfly Walks), In a garden this could be done daily, but even weekly will give useful information.
5. It is possible to use insect traps of various types (such as Malaise traps), but this can result in large quantities of material to sort. The advantage is that sampling is not confined to the brief period when an observer is present. However, traps may not be suitable where particular rare insects are vulnerable to such traps, or in public places where vandalism is a restraint. The recorder learns little of the habits of the flies, such as where they breed. All a trap does is to tell you that the hoverfly has attempted to pass through that point on a site, so interpretation of results needs care.
The Hoverfly Recording Scheme is keen to encourage monitoring. It should be noted that the big changes in migrants normally starts in mid to late July and may show various abrupt or gradual changes through to late August - perhaps an ideal summer holiday project. Contact addresses are given above in the section on studying and recording.
SITE EVALUATION
1. Hoverflies are useful for site evaluation in habitats and districts where the fauna is significant in terms of special species or overall species richness.
2. Because hoverflies breed in so many different niches, they are an unusually broad based group of insects:- plant eaters, fungi feeders, flower dependence, saproxylics of various types (sap runs, rot holes, decaying roots, water-filled cavities), semi-aquatic and aquatic. predators on aphids (and some other insects) and ant associates.
3. They are sufficiently well known ecologically and in distribution that, as a relatively popular group of insects, the results of survey can be interpreted with some confidence.
4. Site quality indices can be based on scoring hoverflies according to status. There is a system that predicts the fauna for habitat and geographic area, so giving a basis for assessing the completeness of the fauna for a site (Syrph-the-net; Speight et al, 2001).
5. For woodland faunas there is a list of primary woodland indicators (Stubbs, 1982). This list was revised (in Whiteley, 1987) and needs further revision in the light of more recent experience. There is a similar provisional list for wetland hoverflies in the Sheffield area Whiteley (1995). Morris (1998) gives lists for chalkland, heathland, wetlands and woodlands in Surrey.
6. Some British hoverflies are included in a list of saproxylic site quality indicators for Europe (Speight, 1989).
Species useful in identifying sites of international importance include:-
Brachyopa bicolor, Caliprobola speciosa, Callicera aurata, C. rufa, C. spinolae, Chalosyrphus eunotus, Ferdinandea ruficornis, Hammerschmidtia ferruginea, Myolepta potens, Pocota personata and Psilopa anthracina.
HABITAT MANAGEMENT
Generally the fauna present will be that which has been able to maintain itself under the recent management regime. For instance, if long grassland has been a feature of recent years, then it is no good abruptly changing the whole site into short grassland; you will lose the long grassland fauna yet there may be no significant short grassland fauna that will benefit. It may be that there is a historical short grass fauna hanging on despite the current long grass habitat, in which case a gradual or uneven increase in the area od short grass habitat is a better way to recover the site’s importance.
Continuity of niches is at a premium, but that does not preclude restoring or increasing the range of niches (where the site is large enough and within range of colonisation).
1. Continuity of saprophagous habitat is a key issue for many hoverflies. This applies mainly to lowland ancient woodland where old coppice stools or large trees have long been a feature. Of the two BAP Priority Habitats in England, Lowland beech and yew woodland has a rich saproxylic hoverfly fauna, whilst Lowland wood-pasture and parkland comes out even higher (where veteran beech or horse-chestnut occur, rather than oak).
a) Retain rot holes, sap runs and other saproxylic niches.
b) Large fallen timber, especially that with existing rot, should be retained on site, preferably mainly in the shade and sited on damp soil if moved from where it fell.
c) If public safety considerations require some surgery, try to minimise the pruning and tolerate as much remaining saproxylic habitat as possible. Hollow trees and pollards may survive gales better than sound maiden trees.
d) Stumps may be very important, including the fauna of rotting roots. Thus stumps or old coppice stools should be retained as far as possible. A few hoverflies may colonise shortly after felling. However, the best phase tends to be when a surface stump is crumbling away and looks spent, yet underground the roots are in prime state of deliquescent decay.
e) A succession of trees of different ages is essential to provide for habitat continuity. Planting of new trees may be necessary if natural regeneration is insufficient (birch is short lived; beech, ash and horse chestnut intermediate c. 2-300 years) and oak long lived 500+).
f) Pollarding prolongs the life of trees and often aids the development of saproxylic habitat. This ancient traditional practice has been revived with good results on various conservation sites.
g) Deer grazing can lead to a flora dominated by grasses and sedges, with the loss of the dicotyledon herbage and flowers that many of the woodland hoverflies require. Deer control is generally desirable.
2. Woodland structure is important.
a) Open structure woodland is generally better for hoverflies than dense stands/canopy.
b) Glades and rides are generally beneficial, with a preference for a variety of openness/aspect. Many hoverflies are edge species.
c) A range of hoverfly flowers through the season should be the aim of management, both in sunny situations and in the shade:- sallow, sloe, hawthorn, hogweed, bramble, angelica, devil's-bit scabious and ivy for example.
d) Coppice suits hoverflies providing the flora responds with suitable flowers during the rotation (generally ride quality remains critical). Old coppice stools can support some saproxylic hoverflies (e.g. ash for Criorhina).
e) Woodland edge is significant. Intensive agriculture hard against a wood is poor compared with a fringe with grassland and scrub with suitable flowers.
3. Grassland, marsh and fen mosaic structure is crucial In the absence of grazing, vegetation can become very densely rank, yet over-grazing can severely impoverish much of the invertebrate fauna, hoverflies included. Much of the fly fauna is associated with taller herbaceous vegetation and at edges with scrub or short vegetation. Fewer species thrive on short dry grassland, though the fauna is more varied in wetter places.
a) Pony grazing, as in the New Forest, can reduce the stature and floristic composition of grassland to a closely shaved lawn, and where access is gained, can degrade the ground flora and flowering shrubs in woodland. In fields and meadows, horse grazing needs to be at sufficiently low level that a mosaic of taller and flower rich herbage remains. The same is true of Konic ponies grazing wetlands.
b) Sheep grazing is often over-intensive. Blitz-grazing ('flying flock' etc.) can result in too traumatic a change in vegetation structure and eliminate important nectar sources. Low level grazing that permits a mosaic of short and long vegetation is ideal. Some of the older breeds of sheep are more effective at scrub control that modern commercial breeds.
c) Cattle grazing is probably the best overall type of stock since grazing is by pulling rather than close nibbling. If stocking is not intense, it should be possible to achieve the ideal of tussocky structure or mosaic of tall and short vegetation, and trampling may brake-up dense tall vegetation and create some minor beneficial poaching in wet and dry ground. Some of the old traditional breeds are best able to thrive on rough herbage and scrub.
d) Ant hills in grassland, formed by the yellow hill ant Lasius flavus, are the breeding site of the RDB hoverfly Microdon devius.
e) Where wet ground is a feature of a site, the soil or peat ideally needs to remain wet, or at least very moist, even during summer droughts. Be careful that creation of a pond does destroy or not drain marsh or wet fen. Ditches may need sluicing.
4. The aquatic and subaquatic fauna is substantial.
a) The margins of lakes,ponds and canals support a number of hoverflies which breed in marginal mud or emergent plants. Of the latter. for instance, reed mace Typha latifolius supports various aquatic larvae that live underwater between the leaf sheaths (so some tolerance of this invasive plant is desirable). Also, various none-aquatic hoverflies specialise in living here as well, including some whose larvae feed on the aphids of waterside plants.
b) Margins of sluggish rivers with muddy edges and emergent vegetation can support the sort of hoverflies found at the margins of still water. Swifter and sharp-sided rivers are generally unsuitable for hoverflies.
c) The margins of small streams are useful to hoverflies where the margins are gently sloping and marshy, and the associated flowers may be very important even to hoverflies breeding in adjacent habitats. For the most part open situations and lightly shaded woodland are best. Some saproxylic hoverflies are associated with dead wood fallen into woodland streams and related wet margins.
d) Springs and groundwater seepages in both open and wooded habitats can support important hoverfly faunas. Where grazed, there is a need to ensure that taller vegetation and flowers remain at least as a mosaic; cattle grazing is best (see above).
e) Ditches need to have marshy vegetation on the edges or base. Over-deepened sharp-sided ditches are unsuitable for hoverflies, as are those too regularly dug-out. If ditches are fairly shallow or gentle sided, cattle trampling and poaching can create an ideal berm about average water level. Mechanical creation of a berm at water level or gentle sides, even if only on one side, can greatly improve a ditch for hoverflies.
f) Seepages, streams and ditches tend to be treated as incidentals to the primary focus on woodland, fen, meadow or heath type. The management of such features needs positive thought.
5. Heathland habitat mosaic is important for hoverflies. The main components are:-
a) The margins of dry sandy paths and tracks through heather. Public trampling may be an inadvertent management tool to maintain these tracks. Artificial surfacing, including gravelling, of tracks usually ruins them, as does excessive churning-up from horse riding.
b) Wet heath and 'bog' have their special hoverflies, and ponds and stream margins may have others.
c) Verge heath (fringes along road verges etc.) may have a far greater array of flowers through the season than the middle of a heath, both herbaceous as well as bramble, and flowering shrubs such as sallow, sloe and hawthorn. For hoverflies, and indeed many other invertebrates, this is one of the vital heathland habitats. Management needs to ensure continuity of the structure and flower resources (scrub and woodland invasion control may be necessary).
6. Saltmarsh is of most value to hoverflies in the highest zones where rushes or other high tidal flora occurs. Freshwater seepage onto saltmarsh and other brackish fringe communities can be of particular significance. Grazing of saltmarsh, especially by sheep, can lead to tightly nibbled sward that is unsuitable. Such grazing on Puccinellia grassland may not be serious, as far as hoverflies are concerned, if the high zone vegetation fringes remain largely ungrazed. High saltmarsh salt-pans with rotting vegetation may look useless but they are the breeding site of Eristalinus aeneus. REFERENCES
Alexander, K.N.A. 2002. The invertebrates of living and decaying timber in Britain and Ireland. English Nature Research Reports No. 467. English Nature, Peterborough. [Catalogue of species, including hoverflies, with species notes and status)
Ball, S.G. & Morris, R.K.A., 2000. Provisional atlas of British hoverflies (Diptera, Syrphidae). Biological Records Centre, Huntingdon. [Distribution maps, time of emergence and notes on all species. Tabulation shows species status, BAP listing and ancient woodland indicators.]
Gilbert, F. 1986. Hoverflies, Naturalists' Handbook No.5, Richmond Publishing Co. [An introductory selection of species, and with a text geared to educational studies].
Godfrey, A. 2003. Managing Priority Habitats for invertebrates. Volume 15: Syrphidae - hoverflies. Buglife - The Invertebrate Conservation Trust, Peterborough.
Morris, R.K.A. 1998. Hoverflies of Surrey. Surrey Wildlife Trust, Woking.
Speight, M.C.D, 1989. Saproxylic invertebrates and their conservation. Nature and Environment series No. 42. Council for Europe, Strasbourg.
Speight, M.C.D, Castella, E., Obrdlik, P & Ball. S. 2001. Syrph the net on CD. Syrph the Net Publications, Dublin. [Site evaluation and species accounts. Scope European: updates cover extra geographic range].
Stubbs, A.E. 1982. Hoverflies as primary woodland indicators with reference to Wharncliffe Wood. Sorby Record No. 20: 62-67.
Stubbs, A.E. 2002. British Hoverflies (2nd ed.). British Entomological & Natural History Society, Reading. [A complete identification guide to the British fauna, with 190 species illustrated in colour.]
Stubbs, A.E. 2003. Dipterists Forum Starter Pack. [general introduction to study of flies]. Dipterists Forum
Whiteley, D. 1995. Using Diptera for assessment of wetlands. Sorby Record N. 31: 82-83.
