On my way back from pike fishing I checked the hive entrance. Curiously, there were bees leaving and arriving. The bees in near-by hives are a very different colour and marking, and it might be possible that my girls survived after all. Or the bees in my hive are robbers. The weather is warm-ish at present, so I shall leave them for a week, and hope to complete a full hive inspection this week-end.
(Esox lucius, http://en.wikipedia.org/wiki/Esox)