About 75% of North American plant species require an insect—mostly bees—to move their pollen from one plant to another to effect pollination.
Unlike the well-known behavior of the non-native honeybees, there is much that we don’t know about native bees. Many native bees are smaller in size than a grain of rice. Of approximately 4,000 native bee species in the United States, 10% have not been named or described.
About 20%-45% of native bees are pollen specialists, meaning that they use only pollen from one species (or genus) of plants. If that plant is removed, the bee goes away. If bees are removed, the plant doesn't reproduce. Some of the native bees are specialists on the very plants that we use for food, including squashes, pumpkins, gourds, and the annual sunflower.
In almost all crops, native bees are the primary pollinator or they significantly supplement the activity of honey bees. Even crops like cotton, soybeans, and peppers that don’t need a pollinator have a higher yield if they’re visited by bees.