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Salticella fasciata - Dune Snail-killing Fly

Salticella fasciataName: Salticella fasciata (Meigen, 1830)

Family: Sciomyzidae

Common name: Dune Snail-killing Fly

Distribution

Known in the UK from just two coastal loci. On the South Wales coast (Pembrokeshire) records are centred on the Kenfig dunes with records extending westward to Tenby. In East Anglia its stronghold is the north west tip of West Norfolk, extending in both directions along that coast and across the Wash to Gibraltar Point (Lincolnshire).

Distribution map from publicly available, 10km square resolution data on the NBN Gateway. The Pembrokeshire records are currently being processed for incorporation into the map.

European distribution

Distribution by country from Fauna Europaea (click the [Display on Map] button to see a map) shows that it is basically a Mediterranean species. The British records are at the extreme north-west of the European range.

Habitat

Inhabits the sparsely vegetated fore dunes which do not become inundated at high tide and which therefore have strong colonies of land snails of the Family Helicidae. No snails, no Salticella. Whilst adapted for such exposed conditions by a marked hairiness, strong legs and a habit of clinging to larger fixed objects (snail shells, flotsam & jetsam), it seems clear that this species is blown along the coastline occasionally as some of the records are from less than optimal habitats. Loss of suitable habitat may result from the construction of sea defenses and other developments in the vicinity, excessive disturbance of fore dunes by holidaymakers and sea inundation sufficient to destroy land snail colonies. Scarce hosts have been cited in the past as reasons for its scarcity but the scarcity of the particular habitat is sufficient to account for the few records and it may well be more general in its choice of host. Land snails from the Holme Dunes site were identified as Cernuella virgata (very widely distributed). Salticella fasciata has a long season. Presumably activity is related to the activity of the host snails. In an environment where host populations are relatively small and of a high mortality, evolutionary pressures would favour those individuals which oviposited on the last active snails in each season, that is before the snails aestivate. Warm, dry days in early October may be the best times to observe them.

It has been tried as a biological control agent against snails such as Theba pisana, Cernuella virgata, Cochlicella acuta and C. barbara which are species from the Mediterranean region which have become pests in Australia. Although it would lay eggs in the umbilicus of Theba it was found to be ineffective in killing the snail. They concluded that it was probably a saprophage rather than a parasitoid (i.e. the larvae feed on already dead snails)1)2).

BAP

Added in 2007. It would be helpful if more observations were made and the locations of strong colonies were precisely determined. What more encouragement could be needed to take a weekend trip to the seaside in early October to habitats as described above?

1) Paper by James Coupland at Malocollogical Society of London meeting, Canterbury, 24-26 September 1996. Biological Control section
2) Coupland JB, Espiau, A, Baker GH. 1994. Seasonality, longevity, host choice, and infection efficiency of Salticella fasciata (Diptera: Sciomyzidae), a candidate for the biological control of pest helicid snails. Biological Control. 4: 32-37.
 
bap/new/salticella_fasciata.txt · Last modified: 2008/09/17 13:22 by malcolmsmart     Back to top
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