Length 2-3.5mm. Forewing with a distinctive long bent cloud; stigmal vein shorter than marginal vein. Non-metallic, dark head & thorax with or without pale markings; dark brown gaster; dark & paler legs; dark antennae; abdomen petiolate; five tarsal segments. 
Female: antennae with one ring & five funicular segments.
Male: antennae with one ring & four funicular segments.

Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

Flying from February to October.

Parasitoid of Oak galls including Andricus aries, A. corruptrix, A. grossulariae, A. kollari, A. lignicola, A. lucidus, A. quercuscalicis, Aphelonyx cerricola. 

Common and widespread. 

Common but under recorded. 

Robin Williams (Oak Galls in Britain): 
https://www.nhm.ac.uk/resources/research-curation/projects/chalcidoids/pdf_X/Willia2010.pdf