Ichneumon insidiosus can reach a length of about 10 millimetres (0.39 in). This parasitic wasp has a black head and thorax, most of the legs are yellowish, while the abdomen is reddish with a black tip.
^Wesmael, C. (1845) Tentamen dispositionis methodicae. Ichneumonum Belgii., Nouveaux Memoires de l'Academie Royale des Sciences, des Lettres et Beaux-Arts de Belgique. 18(1944):1-239.