the turret of a nest of Diadasia afflicta, a fairly common ground nesting bee that forages almost exclusively on winecups (Callirhoe spp.) The white dots are fecal pellets of Callirhoe pollen. Diadasia afflicta is unusual, perhaps unique, in regularly placing these pellets on the edge of the turret. Individual nests are active for only a few days (a female may construct four or five during her lifespan) and the females regularly extend the turret over several days.l As they place a series pellets each night, older nests will usually have series of rings indicating the age of the nest (assuming the turrets are destroyed by rain or errant feet). These bees often nest gregariously, sometimes in groups of a hundred or more. Usually there is only one generation per year but under favorable conditions (like this year in the Austin area) there may be a partial second generation whose success depends on the length Callirhoe flowering. Male Diadasia afflicta commonly patrol the nest site, at least early in the season, looking for emerging virgin females. Beeflies (Paravilla spp.) are also common at the sites.
Diadasia afflicta, like most solitary bees, is essentially harmless to humans. Females can sting but they are non-aggressive and have a rather mild sting. One would have to grab one with your hand to get stung.
Other local Diadasia also nest gregariously and have turreted nests but only D. afflicta decorates theirs with fecal pellets.