Dead bees in front of the hive

I'm passing this question on indirectly. My grandson, who has taken up beekeeping, asked me and was not satisfied with my answer so I said I would pass it on to the forum for more opinions. His english is very limited so he can't do it directly.
This morning he visited two of his hives in an area populated with a lot of eucalyptus trees. Looking at his hives from the outside he saw large numbers of dead bees spread out in front of the hives. The bees are mostly dried out and with their tongues extended. While watching, he saw (about every 2 minutes or so) some bees from in the hive emerging with a another one they were attacking and stinging and throwing away.
My first thought was poisoning. He felt that this waas highly unlikely since he knows of no cultivated fields in the near vicinity. My second thought was starvation (tongues out) but he says the hives have adequate reserves. The hives seem not to be weakened and look like they are functioning normally. Could it be a disease?
Any suggestions would be suggested.