The European mining bee species Andrena lathyri (Andrenidae) is a narrow specialist of flowers of Lathyrus and Vicia (Fabaceae), from which both females and males gain nectar by primary nectar robbing. Both sexes are equipped with a unique proboscis, which is much longer and more strongly angled than in most other Andrena bees including the most closely related species. The comparison between the shape of the proboscis and the interior of the host flowers combined with field observations revealed that the specialised mouthparts of A. lathyri precisely correspond to the dimensions of the flower interior and the position of the nectary, representing one of the few known examples of a morphological adaptation to primary nectar robbing in bees. For nectar uptake, the bee’s head is inserted laterally under the standard petal before it is moved towards the flower base, thereby slitting the calyx longitudinally to a depth necessary to reach the nectary from inside the flower with the specialised proboscis. Nectar-robbing individuals of A. lathyri are able to adapt their behaviour to the different calyx lengths of their host flower species by slitting the calyx over varying distances. Except for the slit in the calyx, primary nectar robbing by A. lathyri does not damage any flower parts allowing for normal fruit development.