94-12 Sat Jan 2 Bumblebees land by adjusting the set-point of optical expansion rate in a stepwise manner Goyal, P*; Cribellier, A; Croon, G; Lankheet, M; Leeuwen, J; Pieters, R; Muijres, F; Wageningen University and Research, Netherlands; Wageningen University and Research, Netherlands; Delft University of Technology, Netherlands; Wageningen University and Research, Netherlands; Wageningen University and Research, Netherlands; Wageningen University and Research, Netherlands; Wageningen University and Research, Netherlands pulkit.goyal@wur.nl
As flying animals approach a surface for landing, they decelerate to reduce their momentum at impact. This deceleration is based on the radial optic flow that animals can use to compute relative-rate-of-expansion. Our knowledge of how they use these expansion cues to decelerate remains limited. Here, we studied how bumblebees (Bombus terrestris), which are important pollinators in nature and horticulture, use these expansion cues to decelerate during landings over short distances. We used machine-vision techniques to analyse the flight dynamics of 4,672 landing manoeuvres as bumblebees approached vertical platforms with two different visual expansion cues, and in luminance ranging from twilight to sunrise. By using a novel analysis approach focussed on individual landing manoeuvres, we show that bumblebees exhibit a series of deceleration bouts, unlike honeybees that exhibit one deceleration phase in long-distance landings. During each bout, bumblebees keep their relative-rate-of-expansion constant at a particular set-point, and from one bout to the next, they shift to a higher set-point as their distance from the platform reduces. As a result, the average change of set-points with distance occurs at a value strikingly similar to pigeons and hummingbirds. This newly-described landing strategy resulted in relatively quick landings, also in dim light condition and with limited visual expansion cues, and has potential use in autopilots governing landings in flying robots.