rubbing its self against the ground, i guess laying eggs?
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It's not laying eggs, its almost doing the opposite. Beeflies lay their eggs in flight, the females hover over solitary bee nests and "flick" their eggs down the nest hole, or any other dark cavity they come across.
In order to give the eggs a bit of "throw weight", they are coated in a layer of fine dust or sand to make them heavier. The load the sand by "hoovering up" tiny sand particles with the egg laying apparatus, this appears to be what this individual is doing.
Tachinid Recording Scheme
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Lat/Lng: 51.4, -2.6
OS grid ref: ST5970