Osmia rufa or Osmia bicornis is a species of mason bee, and is known as the red mason bee due to its covering of dense gingery hair. It is a solitary bee that nests in holes or stems and is polylectic, meaning it forages pollen from various different flowering plants. These bees can be seen aggregating together and nests in preexisting hollows, choosing not to excavate their own. These bees are not aggressive; they will only sting if handled very roughly and are safe to be closely observed by children. Females only mate once, usually with closely related males. Further, females can determine the sex ratio of their offspring based on their body size, where larger females will invest more in diploid females eggs than small bees. These bees also have trichromatic color vision and are importan