Box and whisker plots of the number of aggressive worker contacts towards active and dead virgin queens and towards dead worker bees. Boxes include the median and the 25th and 75th percentiles; whiskers give the fifth and 95th percentiles; N denotes the numbers of experiments; total observation time = 270 min (90 min/group). The number of contacts significantly differed when workers were confronted with active and dead virgins (Wilcoxon signed-ranks test), but not when dead virgins or dead workers were presented (Mann-Whitney test). The given P values are adjusted according to the Bonferroni method.