A univoltine species, flying from mid May to mid July, exceptionally to late August (Else & Edwaeds, 2018; Stanisavljević, 2000).
Parasites and predators: The sapygid wasp Sapyga clavicornis is a well known cleptoparasite of this bee, having been reared from Chelostoma florisomne nests on a number of occasions. The female wasp apparently oviposits in a sealed cell after first having made a small eccentrically placed hole in the partition; it overwinters as a prepupa or adult (van Lith, 1957). Sapyga quinquepunctata and the chrysidid wasp Trichrysis cyanea may also be cleptoparasites of this species (Richards, 1980; Morgan, 1984). Peeters, Raemakers & Smit (1999) additionally list Chrysis ignita as a possible parasite. Höppner (1904a) records the gasteruptiid wasp Gasteruption jaculator as a parasitoid; Crosskey (1951) records the same species as having been reared from tree stumps containing nests of Chelostoma florisomne. The pimpline ichneumonid Townesia tenuiventris is a confirmed parasitoid of C. florisomne in Finland (Jusilla & Käpylä, 1975); this wasp also occurs in Britain. In France, cells have been invaded by the chalcid Eurytoma nodularis, the ichneumonid Ephialtes carbonarius (almost certainly a misidentification for Townesia tenuiventris) and the beetles Ptinus fur and Trichodes alvearius (Maréchal, 1933); all of these inquilines occur in Britain, although the brightly coloured, showy clerid Trichodes alvearius may now be extinct here (Allen, 1967). Both Chelostoma florisomne and Sapyga clavicornis are sometimes infested by the mite Chaeotodactylus anthidii (Richards, 1930).