1. The local insect composition may be as important as the local floral composition for bumblebees' foraging behaviour. However, little is known about how the local abundance of insects affects the foraging patterns of individuals.
2. Using field observations, we studied the relationships between the local density of previous and simultaneous foragers and the local foraging behaviour of Bombus pascuorum, Bombus lucorum/B. terrestris and Bombus lapidarius while pollinating Centaurea jacea.
3. The number of bumblebees foraging in the plots was positively related to the number of new individuals arriving at these plots. The number of inflorescences contacted and the duration of visits were negatively related to the number of simultaneous foragers, but only in B. lucorum/B. terrestris. The effects of previous foragers on the behaviour of other bumblebees were species-specific and variable in their direction. Such contrasting effects can be explained in terms of bumblebee species' abundances and functional similarity. In some cases, the effect of previous foragers increased with Centaurea density.
4. The local abundance of previous and simultaneous foragers affected the foraging behaviour of particular bumblebee individuals in complex ways. Future studies on local foraging behaviour might benefit from including the abundance of co-foragers.