Renter: Existing cavities. Female Megachile willughbiella nest in borings in dead wood, including rotten tree stumps, logs and posts; also in tree boles vacated by the larvae of the moth Cossus cossus, under bark and in the soil (Niemalä, 1936). Nests in the soil are commonly encountered and in potted plants in greenhouses (pers. obs.). O’Toole & Raw (1991) illustrate a female of this bee building her nest in a length of rubber hose in a greenhouse.
The cell walls are fashioned from leaf discs cut from a variety of plants, including Fagus, Rosa and Hypericum androsaemum. Nests studied by Holm & Skou (1972) each contained only two to six cells and these varied little in size, there being no obvious differences between those containing male and female progeny. However, F. Smith (1876) briefly describes a nest burrow containing thirteen cells, and another in which a single common entrance led to three separate brood burrows. A nest has also been described and figured by Grandi (1961). Provisioned cells are illustrated by Westrich (1989), and Müller, Krebs & Amiet (1997).