Probably oligolectic on Asteraceae. Müller and Bansac (2004) have shown that Megachile marginata has a distinct (e.g.) or exclusive preference for Asteraceae (Carduoideae) and that the species has a modified pollen collecting device is found under the hind trochanter and femur
Composition of scopal pollen contents were studied by Zander (1935). He showed that in a sample of 4 specimens of M. marginata (as M. picicornis), the pollen loads were all Asteraceae; Centaurea jacea type 28.6% & Serratula type 71.4%.