Pollen samples from provisions and faeces found in the nests of fourOsmiaspecies were analyzed by SEM and TEM. The pollen grains studied wereCistus, Sonchustypeoleraceus. Primustypedulcis, andQuercustypeilex. The apertures ofCistusandSonchuspollen stored in the provisions were slightly expanded, and the cytoplasm protruded through them. Conversely,PrunusandQuercuspollen grains showed hardly any signs of such apertural protrusions. Further, the cytoplasm ofCistusandSonchuspollen (which have thin intines) was almost entirely lacking in the pollen grains recovered from faeces, while in the faecal pollen grains ofPrunusandQuercus(with thick intines) the cytoplasm was much less modified. These preliminary results indicate that both the protrusion of the cytoplasm in the provisions and the thickness of the intine may play an important role in the digestion of pollen grains byOsmiabee larvae.