Brachyopa insensilis Collin, 1939
Prior to 1939 the only listed British species was B. bicolor. The additional species were not covered by a widely available key until Coe (1953). Consequently, records prior to 1953 must be based on verifiable specimens.
Biology & ecology:
The larva occurs in sap runs or accumulations of sap under the bark of trees. Although traditionally associated with Elm Ulmus, it has been found on a wide range of deciduous tree species including Ash Fraxinus excelsior, Beech Fagus sylvatica, Lime Tilia sp., and particularly Horse Chestnut Aesculus hippocastaneum, often in urban and suburban situations. Adults are usually found sitting on tree trunks or on nearby vegetation. They can often be seen hovering in small groups immediately in front of a sap run. Stirring up a sap run (presumably releasing odours) can often result in the rapid arrival of adults.
A very widely distributed species that is undoubtedly under-recorded. It is most likely to be found in urban areas where Horse Chestnut has been planted.
Status & conservation:
A steep rise in records in the late 1980s reflects improved knowledge of how to find them. Once this burst of enthusiasm faded, recording returned to previous levels, suggesting that the population is stable. Notable according to Falk (1991), but Ball & Morris (2014) demoted it because it occurs in many more than 100 hectads.