Digging behaviour and responses to photic and gravitational cues as elements of escape behaviour of bumblebees.

We have investigated escape behaviour of workers of two bumblebee species, Bombus terrestris and B. pascuorum, when confined to test tubes plugged with soil and either exposed to sunlight or kept in darkness. In both these situations B. terrestris performed better (i.e. escaped after a shorter time) than B. pascuorum. B. terrestris (but not B. pascuorum) also performed better in darkness than in tubes exposed to sunlight. This implies that in both situations B. terrestris showed higher readiness to dig than B. pascuorum, and that in tubes exposed to sunlight only B. terrestris showed high readiness to display photopositive behaviour as well. B. pascuorum displayed, however, photopositive behaviour in another escape situation: when released in a dark room in front of a vertical array of four sources of white light. In that situation, B. pascuorum also displayed the tendency to fly upwards, based most probably on responses to gravitational cues.