Large males vigorously defend clumps of favoured flowers and will intercept and chase away any other insect which enters such a territory. Males have even been known to kill such intruders (by crushing them between the ventral surfaces of the flexed down abdomen and the thorax). Females are allowed to visit the flowers and it is at these sites that mating takes place. Resource defence polygyny, as this behaviour is called, is discussed by Severinghaus, Kurtac and Eickwort (1981) and is summarised by Thomhill and Alcock (1983). Females select existing cavities as nest sites, examples including insect exit burrows in dead wood, hollow stems, crevices in the mortar joints of masonry, burrows in the soil, and various man-made objects. The cell walls and closing plug of the nest are fashioned from compacted layers of long, silky hairs which are shaved off leaves by the female's multi-dentate mandibles. Favoured plants are woundworts (Stachys lanata [s. byzantina]), yarrow (Achillea millefolium), great mullein (Verbascum thapsus), Pelargonium, cotton thistle (Onopordum acanthium) and house-leek (Sempervivum). Hairs are brought to the nest site in a ball and applied to the inner surface of the cavity by teasing them out with the mandibles; the gaster is then used to tamp down the hairs (A Raw, pers. comm.). The species has earned the colloquial name 'wool-carder bee' from this habit.