Ants!

When I wandered over to watch the bees yesterday, I was dismayed to see a line of ants entering the old hive entrance.  I went around to the back of the hives and there was a line of ants crawling up one of the hive stand legs.  The legs are in cans with water to prevent such an event.  However, one of the screens I had put on the legs to keep the bees from falling into the water had tipped down and was touching the edge of the can allowing the ants a safe passage.
I immediately adjusted the screen and removed the ants I could see from the back of the hives and the stand.  I took a look inside the tops and there were many ants inside the new hive's vivaldi box.  These met a quick demise. (There were bees there, too, but they ignored me.)  No ants inside the top of the old hive.  There were a lot of ants inside both of the trays; naturally, there's a lot of good eats in those trays.  I scraped the trays clean.
I'm certain there are still a lot of ants running around the hive, but since they cannot return to the hive nor can there be any replacements, I figure eventually they will be gone. That is, as long as I keep the screens off the cans, the cans filled with water and no plants touching the hive stand or hives. Ants can live for several months.

After the line of ants was brushed off

Ants are a huge problem for beekeeping in this area.  Jeremy Rose says they are perhaps a worse pest than the varroa mite.  If enough ants get into a hive they can kill it in a few days by eating honey, pollen and brood.  The bees are bothered by them but cannot kill them or remove them.  An invasion of ants is one of the reasons the bees will abscond.
Addendum:  When I checked the hives this morning I found (and got rid of) only about 15 ants.