Flight performance
Hornets and honey bees had different flight performances in term of flight speed, curvature and static flight (Figure 3 ). Honey bees leaving the hive were 1.9 times faster than honey bees entering the hive, and honey bees entering the hive were 1.25 times faster than hornets (Kruskal-Wallis chi-squared=78018, df=2, P<0.001; Pairwise Wilcoxon test, P<0.001; Figure 3a ). With respect to flight curvature, the flight trajectories of honey bees leaving the hive were significantly. straighter than for honey bees entering the hive, and for the latter the trajectories were significantly straighter than for hornets (Kruskal-Wallis chi-squared=41384, df=2, P< 0.001 ; Pairwise Wilcoxon test, P<0.001). Moreover, the curvature was less variable in honey bees leaving the hive compared with the two other categories (Figure 3b ).
Hornets hovered significantly for more time than honey bees (p<0.001 (Pairwise Wilcoxon test), hornets hovered 2.1 times more than honey bees entering the hive). Honey bees leaving the hive hovered significantly less than the honey bees entering the hive (Kruskal-Wallis chi-squared=27949, df=2, P<0.001; Pairwise Wilcoxon test, P<0.001) (Figure 3c ). In hovering hornets, static flight as defined by “threshold 1” (no more than 2mm displacement) represented a very small proportion of flight time, under 10%, while if defined by “threshold 2”, up to 10mm displacement, hovering hornets can be divided into mainly two categories. A smaller group of hornets, spending 10% of recorded flight time hovering, and a larger group of hornets spending around 90% of recorded flight time hovering, demonstrating that this kind of flight pattern is used by many for long periods of time in front of the hives (Figure S2 ).