A nationally rare fly that’s dependent on the Smooth-gastered Furrow Bee (Lasioglossum parvulum). It belongs to a group of flies known as satellite flies because they follow their host bees to their nesting sites. The fly lays its eggs in the bee’s nest and the larvae feed on the pollen and nectar the bee collects.
This fly has only been recorded seven times in the UK since 1960, all in southern England and southern Wales. In Devon it’s only been found at Halsdon Nature Reserve (managed by Devon Wildlife Trust), where a vast colony of furrow bees nests in the soft, eroding banks of the River Torridge.
The fly’s main threats relate to the furrow bee and include loss of the riverbank due to high flows and flooding, and, if cattle are prevented from accessing the river’s edge, too much stabilization and excess shading from trees.
Actions
Maintain open banks along the River Torridge at and near Halsdon Nature Reserve by removing encroaching trees and allowing cattle to access the river.
Where to focus action
High Opportunity Areas: Watercourse corridors – Halsdon Nature Reserve on the River Torridge. See Mapping. Use the search function to find Halsdon Nature Reserve by clicking Devon Wildlife Trust reserves and typing in Halsdon (or open the Devon Wildlife Trust reserve layer under Other Useful Layers> Land Ownership Opportunities> Devon Wildlife Trust Nature Reserves).