Two fly species are occasional minor predators of leafcutter and mason bees. The larvae of the dewy bee fly (Anthrax irroratus) are occasionally found feeding on immature bees. Two spikes projecting from the head of the immature fly are used to break through cell partitions.

Physocephala texana, a conopid fly, briefly lands upon foraging adult bees and deposits an egg through the bee’s abdominal intersegmental membrane. The egg hatches, and the larva consumes the bee from the inside out. Adult bees killed by this fly are recognized by an elongated abdomen containing the fly pupa. No known control measures exist for either fly species.