Actually, these Andrenid bees never left town. These small native bees spend most of the year underground and emerge every spring. I have written about their biology before.
One question I have always had about these bees is: “What do they eat?” Looking around the neighborhood I don’t see many flowers. I have seen the bees loading up on camellia pollen but that is certainly not what they evolved to do. What are these little bees eating in urban and suburban habitats and what plants did they evolve with?
In my yard I have four plants blooming: Crocus, Oregon grape (Mahonia aquifolium), native pachysandra (Pachysandra procumbens), and witch hazel (which is really about finished). Oh, pansies are also blooming.
Looking on the ground this is all the bees have. Looking up, though, I see red maples blooming which are an important early season pollen source for native and honey bees. Other trees like red bud are also starting to bloom.
Elsa Youngsteadt, in my lab, is doing some initial work on these bees and what types of pollen they collect and how they use red maples, which are one of the most common street trees. This will compliment some of the other native bee research being done by April Hamblin and Margarita López-Uribe.