Bioblapsís mallochi sp. n., from Scotland is described and a key is given to adult Bioblapsis. The host of B. mallochi is the syrphid Cheilosía longula, which breeds in fruiting bodies of Boletus fungi growing in the ground flora of pinewoods. The host of Bioblapsis polita (Vollenhoven) appears to be species of the hoverfly genus Ferdinandea which are associated with sap-flows on deciduous trees. These are unusual host species for diplazontines which are more typically associated with predacious hoverflies.