Robber bees

[crane]

I have two hives going right now. Went to check them and there was a LOT of activity around the entrances of both hives. At first I thought it was orientation flights, but not likely both at the same time and there was too much commotion around the entrances. I realised it was a robbing situation. I had both entrance limiters at the 4 inch openings and it wasn't stopping any bees. I switched them to the smallest opening but they are not quite as numerous but haven't gone away completely yet.
It's hot as the dickens in Texas right now and I don't want to get them too hot with no ventillation and make them swarm.
Anything I can do?

[FRAMEshift]

Orientation usually peaks in the early afternoon.  It's not unusual for the hives to be doing it at the same time.  Robbing usually involves more frantic flying while orientation is a bit more leisurely.  Also, I've noticed that when robbing is underway, there will be lots of bees probing for entrances on the sides and back of the hive.  They will sometimes move from the side toward the main entrance in a rush, trying to sneak in.  There will usually be fighting around the entrance too.  Did you see any of those signs?

[crane]

Yeppers for sure. Anyplace they think might be an opening they check it out. I am sure they are robbers. They seem to be unencumbered by the resident bees and are just having a fine old time. This is my first year and I am really at a loss to what to do next. I have read that I should move the hive, take a wet sheet and throw over the hives, or just close off the hive completely for a few days. Thing is, it is so darn hot right now that I am afraid the bees will cook in the closed up hive.
I have the entrance reduced to about a half inch but the robbers are just clumping at the entrance and walking right on in.
Any ideas would be appreciated.

[FRAMEshift]

You could put on robber screens.  They cover the entrance with a screen and the resident bees know to go around it but the robbers don't. 

You could close up the hives for a couple of days.  If you do that, I would add water to a frame of empty comb so they will have water for drinking and for evaporative cooling.

Do you have any idea where the robbers are coming from?