Andrenas are commonly referred to as “mining bees,” because they construct underground nests. In mid-March, if you scour the ground along park trails, you may spy the holes of Andrena nests, usually no more than half an inch wide, partially buried among leaf litter. Andrenas are solitary nesters — they do not form colonies like honey bees and do not swarm in attack.  Nevertheless, Andrena mining bees nest close by one another, sometimes forming collective populations numbering in the tens of thousands. In such “bee cities,” each female usually builds her own nest and individually supplies it with food.
Photo by Kristi DuBois on 5/1/20 in the Blackfoot River area east of Missoula, MT.