Here's the short version: Yesterday around noon I put syrup in a hive-top feeder. Within about two hours, a frying pan filled with water a few hundred feet away had bees everywhere. When I went to dump the dead bees at dusk, the pan was actually filled with very thick syrup, and the dead bees were glued together in sticky clumps.
More info: The temp was in the mid 70s yesterday, and I needed to feed a hive. I made a mixture of 4#s sugar, one gallon of water. I poured about half in the feeder. My hive is in the backyard, approximately 300 feet away. I keep a frying pan on the other side of the house filled with water, for any of the off-leash dogs in the neighborhood. It is generally ignored by the bees, although the gutters around the house attract them. However, my entire front yard was filled with bees, so much that I searched the trees for an early swarm. I noticed that they had completely covered the frying pan. Down the dead-end street a few hundred feet away, my in-laws have about a dozen hives, all of which have feeders on the top, but have only been feed dry sugar. My hive drank the half-gallon by twilight, and drank another half-gallon through the night. I didn't remove the feeder, but peering through the plastic, it looked like I hadn't really lost any bees. It's still a vibrant colony, other than not having enough winter stores without my help.
So, I'm wondering:
1) Was my hive robbed by the others, and they gathered at the pan for more water?
2) Was my syrup too thick, and my bees needed more water?
3) Did my bees regurgitate the syrup outside of the hive for their own reasons?
4) Were the bees in the front yard the ones that had been feed dry sugar, and it had nothing to do with my hive?
5) Something else altogether.
I can only reply to your second question. I think your syrup was actually too thin. Ratios are pounds (sugar) to pounds (water, which is about a pint.) I would have fed 2:1, sugar to water. It's late, but I think you made the opposite, 1:2.