Essex Red Data hoverfly statuses

by R.G. Payne

The Syrphidae, collectively known as hoverflies are among the better known families of two-­winged flies (Diptera). Many are familiar to the general public and they are the most popular group for study amongst Dipterists.

The British Hoverfly Fauna There are 270 species of hoverfly currently known from Great Britain. As a group, they are very useful biological indicators. The food and habits of the larvae are extremely diverse and the adults are found in a wide spectrum of habitats.

The Essex Fauna 183 species of hoverfly have been recorded from the two Watsonian vice counties of Essex. This is 68% of the total British fauna. Of these 183 species, 8 spp have not been recorded for 50 years (4%), 50 spp are considered rare (27%) and 46 spp are considered scarce (25%).

Regional Status Categories Since 1980, hoverflies in Essex have been recorded on a 1 km square basis. By far the most abundant and ubiquitous species is Episyrphus balteatus, a species recorded from every 10 km square and 424 1-km squares. The total number of 1-km squares in Essex is 3958, therefore E. balteatus has been recorded from 11% of possible squares. This can be used as a base-line from which the scarcity of other species can be compared using methods described in Harvey 1998.

• Essex Extinct species: Species not recorded in the county for more than 50 years.
• Essex Rare species: Post 1970 records (records from Payne, R.M. are included) from 1% or less of the total number of 1 km squares from which E. balteatus has been recorded.
• Essex Scarce species: Post 1970 records from more than 1 % to 5% of the number of 1-km squares from which E. balteatus has been recorded.

National and International Status The latest Biodiversity list for East Anglia (May 1998) lists species of conservation concern in East Anglia (Cambridgeshire, Essex, Lincolnshire, Norfolk and Suffolk). There are six species of hoverflies recorded from Essex which are included. These are:­

• Anasimyia interpuncta
• Callicera spinolae
• Lejops vittata
• Paragus albifrons
• Pocota personata
• Psilota anthracina
• Sphaerophoria loewi

In addition, the following species are long list species included in the Biodiversity U.K. Steering Group report.

• Callicera spinolae
• Didea alneti
• Doros profuges
• Eumerus ornata
• Lejops vittata
• Pocota personata

These species are considered globally threatened or declining species throughout their range.
National Rarity Categories National rare species are those included in status categories defined in the British Red Data books (Shirt, 1987) and provisionally updated by Falk (1991).

Red Data Book (RDB) species are defined as those species occurring in up to 15 10km squares in a national context. There are 4 categories.

• RDB1 (endangered). These species are in danger of extinction and their survival is doubtful if causal factors continue to operate.
• RDB2 (vulnerable). These are species considered vulnerable and likely to move to the endangered category in the near future if the causal factors continue to operate. They include species which are declining throughout their range, are in vulnerable habitats or where populations are low.
• RDB3 (rare). These are rare species with small populations, not presently endangered or vulnerable but which nevertheless are at risk. Species in this category are estimated to occur in 15 or less localities.
• RDBK (insufficiently known). These species probably fall into one of the above categories but present information is inadequate.
• Nationally Scarce These species fall within the Nationally Notable categories introduced by Ball (1986). They are estimated to occur within the range of 16-100 10 km squares since 1970.
• Local A subjective category meaning the species is not infrequent but has a localised distribution.

ESSEX RED DATA LIST Threatened Essex Hoverflies It is important to attempt to assess the degree of threat to which rare Essex hoverflies are subjected. Many important habitats are very vulnerable to changes in management, wholesale destruction or fragmentation.

Following Harvey (*1998) these threat categories are defined as follows:­

• Endangered
  • Known as a single extant population within a single post 1970 one Km square or from a single threatened or vulnerable site in the county.
  • Species not recorded in the county for more than 50 years and believed extinct.
• Vulnerable
  • Known as a single extant post 1970 population in the county, but for which further populations are considered probable.
  • Rare species in Essex, restricted to habitats
  • Species which only occur at sites within the county known to be vulnerable.
  • Species showing a decline in population over the last 20 years and are known from 5 or fewer post 1907 one km squares.
• Threatened
  • Scarce or rare species with isolated populations within the county.
  • Scarce species restricted to habitats or sites known to be under threat.
• Regionally Important
  • Species which are important in a national context because the county contains a significant proportion of the national populations.
  • Species important in a national context because of their close association with specific threatened habitats which have BAPs.
  • Species important in a national context because they are associated with or peculiar to a specific habitat for which the county is especially well endowed.

Essex Red Data List