hellow folks
I am a beekeeper by trade that by the way does not make me an expert, but i do have a fair clue some of time. sounds to me as if one of your nieghbors has become a beekeeper. A wild hive is still a strong possibility,again this would also probably be the result of a local beekeeper the bees dont always like the house you give them and they go looking for a better place to live.
mites are still a problem for those of us that keep bees and it has added greatly to our work load. so any more in areas were there are ample numbers of beekeepers you will also have a few wild hives. but they usaly die off in a few years.due to all kinds of problems, mites weaken the bees and make them suseptable to many diseases. Often in an area with a good source of new bees, a wild hive "bee tree" will die off after a year or two and a new swarm will move into the now empty nest and it apears to live for many years.
as for the statement of the bees get short tempered in late summer, there is some truth to it, but this only has bearing around thier hive were they are guarding their winter stores of food. generaly speaking.around your flowers they do not have anything to protect and are not likly to get aggresive. having a local hive can only help your garden out.you can only hope the hive is close enough to do you any good . as in late season as jvs has stated nectar can be scarce and the bees will travel a long distance to gather it at a good source.this looks like a good place to stop.but i am always ready to talk bees with anybody. please forgive spelling and typos i am not that good at useing the computer D.C. Don