This hoverfly feeds on micro-organisms associated with decomposition. Adults are present during summer, and feed on nectar from plants such as bramble (4). The eggs are laid in wet rot holes on fallen or standing dead aspen trees (3). The larvae then develop in the wet rotting wood below the bark (2).
Before 1990 this fly was known from just eight Scottish sites. It has not declined since it was first discovered in 1905 and has always been one of Britain’s rarest hoverflies (4).The fly is now known to occur in 12 sites in northeast Scotland, after a thorough survey by the Malloch Society (4). It is thought to be endangered in Europe (2).
This species is an indicator of ancient woodlands (2). It is found only in large mature aspen (Populus tremula) woodlands or pine and birch woodlands with some aspen (4). Only stands of aspen larger than 4.5 hectares in size are suitable to maintain this species (2).
Large stands of aspen are rare in Britain; aspen stands have been damaged by road building, and underplanting with conifers. Furthermore, in many woodlands fallen wood is often removed and rabbits or deer may feed on the bark of fallen trees, which removes the unique habitat of this species. This species requires a constant supply of dead wood, but at many sites a suitable range of trees of varying age structures is not present; saplings are often browsed and killed by deer and rabbits, while forestry techniques tend to result in a lack of mature trees (4). A further threat is that of over-collecting by entomologists (4).
The aspen hoverfly is a priority under the UK Biodiversity Action Plan (UK BAP) and a Species Action Plan has been produced in order to coordinate conservation action targeted at this species (2). The RSPB has taken on the role of ‘lead partner’ for this and another rare hoverfly, the pine hoverfly (Blera fallax) since they were found on RSPB-owned sites. With Scottish Natural Heritage, they are funding a programme of work on these species, carried out by the Malloch Society (for details of this work please follow the link below) (4). Two of the woodlands supporting this species are designated Sites of Special Scientific Interest (SSSIs) and one is a National Nature Reserve (NNR). The UK BAP Species Action Plan aims to maintain all known populations, enhance the size of these populations and to reintroduce the species to three sites by the year 2010 (4).
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