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This species is mainly present in Austria, Belgium, Great Britain, Czech Republic, Finland, France, Germany, Greece, Hungary, Italy, Poland, Romania, Russia, Slovakia, Spain, Sweden, Switzerland, in the East Palearctic ecozone and in the Near East.
The head and thorax are completely black. The head is strongly rounded, the thorax is elongated in a sort of long neck (propleura), which separates the head from the body. Also the abdomen is strongly stretched, broader at the posterior end and placed on the upper chest (propodeum). The colour of the abdomen is black, with reddish-orange rings. The tibiae of the hind legs are club shaped. In the female the ovipositor is usually very long with a white tip. In resting position, these wasps slowly and rhythmically raise and lower the abdomen.
The females of this parasitic wasp lays its eggs by its long ovipositor on the body of larvae of solitary bees or wasps. On hatching its young larvae will devour grubs and supplies of pollen and nectar of its victim. The adults grow up to 10–17 millimetres (0.39–0.67 in) long and can mostly be encountered from May through September feeding on Apiaceae species.
Gasteruption jaculator have been found visiting various flowers, or hovering around the nests of solitary bees and wasps in gardens and meadows.They are commonly found during May to September.