There are only two colonies of this gold, green and black fly known in the UK. The single colony in Wales is in a perilous state as the habitat has deteriorated and for many years attempts to get the habitat into good condition through Site of Special Scientific Interest (SSSI) related government payments failed to produce the target habitat. However, in 2008 CCW instigated some positive action to ensure that the Welsh population survives on the Banc y Mwldan SSSI. Management action and monitoring will need to continue to see if action has been in time to save the population.
|Barred green colonel soilder-fly (Odontomyia hydroleon) © Josef Horcicka|
What does it need?
The Barred green colonel (Odontomyia hydroleon) is only found in open, calcareous (lime rich) seepages in which its larvae are aquatic or semi-aquatic. The ecology of Banc y Mwldan is very unusual since it is situated on a very localised outcrop of calcareous sandy drift. The drift is/was quarried for sand on the other side of the road uphill from the fields. Adults visit the flowers such as Hogweed (Heracleum sphondylium) for nectar.
|Hogweed (Heracleum sphondylium) © Dr Chris Gibson|
What is its British conservation status?
In Great Britain this species is currently classified as Endangered and is protected under the NERC Act as a species of ‘Principle Importance’ for the conservation of biodiversity.
Since its discovery at the Welsh locality in Ceredigion in 1986, the population has declined and the species went missing from 2000 to 2005 when two were observed on one day. Since then monitoring has been undertaken in every year, three adults were recorded in 2006, but it was visited too late in 2007 and there was poor weather in 2008 and 2009. There is no suggestion of decline at the Yorkshire locality although the population is small and localised.
Why is this species under threat?
This particular little animal is threatened by loss of open seepages due to lack of grazing, loss of adult nectar sources due to overgrazing (these are not necessarily mutually exclusive), operations which damage the hydrology of the seepages such as quarrying and groundwater abstraction.
Threats to the Ceredigion population
The site is notified as an SSSI and a management agreement between the landowner and the government agency Countryside Council for Wales (CCW) has been in force for many years that specifies a grazing regime which should maintain an open structure to the seepages. The Welsh population is the subject of a monitoring programme coordinated by CCW.
In 2005 the report compiled for the UK Biodiversity Action Plan said – “Occupied seepages and fen at Banc y Mwldan are now very rank and require urgent management to create and more open structure.”
The fields used to be rough grazed by cattle, and this is thought to be the most appropriate management to prevent the tussock sedge smothering the open seepage/stream puddles in which the soldierfly breeds. For Barred green colonel the most important field has seepages turning into a stream. CCW made the site an SSSI and formulated a management agreement with the grazier/owner to continue to carry on with the traditional management. The grazier reduced grazing significantly, yet continued to be paid for management that was not being carrying out.
In recent years the fly has only been found in the southern fields of the SSSI and is thought to have become extinct in the northern fields.
In 2007, seepages in the northern field were fenced and in 2008 and 2009 these were strimmed and horses grazed the seepage zone. In the 2008/9 winter there was a lot of scrub clearance to further open up the site. It is hoped that heavy grazing and scrub clearance will create habitat that the fly can recolonise from the southern fields. It is hoped that in 2011 the population will increase as the new areas are colonised. More work will then be needed to get the southern fields into ideal condition.
There is also a quarry adjacent to the SSSI but the hydrology of the fly’s habitat does not appear to have been damaged.
Threats to the Yorkshire Population
The site in Seive Dale is a Yorkshire Wildlife Trust Nature Reserve and an SSSI within Forestry Commission land. It is on a sheltered valley side, partly within unimproved grassland and partly in fenced peaty carr. There are excellent calcareous springs with spreads of tufa (coral like lime deposits) and transitions into wet vegetated areas. Barred green colonel was found in the early 1990s. In recent years invading scrub has been removed, in conjunction with grazing, following which the numbers of the soldierfly have increased (Roy Crossley pers com.).
The southern fringe of the North York Moors contains an array of calcareous seepages and springs, many of them with individual character. Despite surveys no other Barred green colonel site has ever been found.