Univoltine with an extended flight period. Females are found from late April to August (exceptionally September and early October), males from early August to the end of September; G.M. Spooner (pers. comm.) collected a male in mid May.
Label data from a few Spanish specimens shows that females are active from (at least) March to June. (Ortiz-Sanchez & Pauly, 2017)
Parasites: G.R. Else (pers comm.) found female Sphecodes reticulatus on several occasions flying in the vicinity of the nesting burrows of L. prasinum. Morice (1910) and Alfken (1913) cite this Sphecodes as a cleptoparasite of the species; E. Saunders (1896a) was also inclined to think it associated with it. Nevertheless, positive proof rather than speculation, is still awaited.