Foraging animals can choose to act as predators or not depending on the level of
defensiveness of the potential prey. This requires prior evaluation of prey
defensiveness, which can be variable, e.g. young insects are usually less able to
defend themselves. Here we show that small hive beetles, Aethina tumida, which are
scavengers and parasites of honey bee, Apis mellifera, colonies, are facultative
predators of young adult host workers. Adult female beetles mounted and attacked
young workers more often than their older nestmates, indicating that the beetle is
assessing the defensiveness of the host and is adjusting its behaviour accordingly.
Since adult female beetles need proteins to activate their ovaries, predation on
defenceless young alive host workers offers another rewarding food source, which
can obviously not be exploited by beetle larvae. In conclusion, adult small hive
beetles seem to be able to assess the trade-off between safety and food reward.