Male black bees (mason bees)will hover around nest entrances, chasing away intruders. They lack a sting, though, so just ignore them. Females do sting though, but only if you actively bother them.
Black bees (mason bees) overwinter as adults, in vacant nest tunnels. In spring, when it begins to warm up, the adults emerge and mate, then the males die and the females begin working on new tunnels or enlarging tunnels from previous years. She will construct brood cells, load them with food, and then lays an egg in each cell.
Eggs hatch within a few days, and the young larvae feed on the food left by the queen. In 5 to 7 weeks, depending on weather conditions, the bee reaches adulthood and leaves the brood nest in late summer to feed on nectar before settling in for the winter.
This bee is a very useful pollinator and with a bit of help from you, it could help replace the beleaguered honey bee. All you need to do is provide them with nesting boxes. Take a block of wood and drill some 5/8 holes in it that are about 5 cm deep, drill the holes about 2 cm apart, and drill 3 sides of the block. Take another piece of wood that is about 10 cm wider on 3 sides and place it on top of a roof. Place this out by your garden and let the bees fill it up.
In the fall after the bees have filled the holes, you can move the block to a dry place, carport, or shed, and let it sit until spring. Then, when the weather begins to warm, move the block out into a warm and sunny place and the bees will emerge and go about pollinating your gardens. Build many boxes and get many bees. If you drill the holes less than 5 cm deep, the new bees will be males and if the holes are deeper than 5 cm the new bees will mostly be female, so drill about an even amount to ensure mating goes well after they emerge.