The ground-nesting bees of my previous post are "sweat bees," in the genus Halictus.
Sweat bees get their name because they are attracted to perspiration (and lick it up).
But the most interesting thing about sweat bees is their social behavior.
Many sweat bees are very flexible about roommates. They are solitary bees sometimes, and sometimes co-habitate. When they co-habitate, using the same nest entrance, one female might be the 'egg-layer' and she will aggressively keep the others them from laying eggs. Subordinate females (usually daughters of the principal egg-layer) will make foraging trips, stand guard at the entrance, or work on underground construction projects.. and if something happens to the dominant female, a subordinate will step into her place. If the group is big enough, subordinates can get away with laying eggs anyway. And sometimes there is no queen at all, or the females are all unrelated and have a more communal arrangement.
Here are 2 females from the same nest. On the left is the 'guard' bee. The other (on the rock) just returned from a foraging trip. Once the guard recognizes a nestmate, she will move aside.
Watching bees doing their thing... oh man.. bees make the best pets!