Nest construction and behaviour in the nest of the female and the larva of Panurgus banksianus was studied. The nest has an excavation gallery and a special tumulus-free entrance. Several laterals are made from the descending gallery, and ten cells were found in one nest. A nest with one cell is completed in one day and the excavation of a new lateral takes about 2 I/2 hours. A new entrance is often tunneled out when 4 or 5 cells have been made in a nest, and the former entrance is then used as an excavation gallery. The cell has a conic, lined neck. During provisioning the female stores the pollen as a loose heap, and the pollen sphere is not formed until about I hour 45 min. after the last provisioning flight. The curved egg is firmly attached with its posterior end on top of the sphere. During the feeding of the larva it gradually glides down to the floor of the cell, but its venter is maintained apposed to the provisions and the anterior towards the cell-closure. The provisions are consumed in about 2 weeks. When the larva starts defecating, the pellets are attached to the wall of the cell. The pupal stage begins about the Ist of June in northern Denmark, lasts about 3 weeks, and the adults spend 3 days in the cell after hatching. An absolute minimum of 8000 host plants per day was required for the I70 ♀♀ of the colony.