Bumblebee populations are declining in the United States for a range of reasons—loss of habitat, pesticide use, climate change, competition from non-native species, and non-native parasites. As major plant pollinators, bumblebees are important to plant reproduction and the overall health of ecosystems. As the abundance of these large hairy bees has dropped in recent decades, scientists have held out hope that smaller native bee species can step in as efficient and effective alternative pollinators.