Robber‐like pollinators: overwintered queen bumblebees foraging on Corydalis ambigua

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Abstract
The behaviour of nectar‐collecting Bombus hypocrita sapporensis Cockerell queens was observed on a population of a spring ephemeral plant Corydalis ambigua Cham, et Schlecht. Daily patterns of activity and behaviour changed with the progress of flowering. Activity peaked shortly before sunset early in the flowering season but approximately at noon towards the end of flowering. In the peak flowering period the queens tended to visit nearby plants and to change direction often, whereas early or late in the flowering period they flew further between visits and were less likely to change direction. Each plant was visited 0 to 24 times (mean 9.4 ±SD 5.2) by the queens during the whole flowering season. The queens collected nectar, rarely through the front of the flowers but mostly through the spurs perforated by themselves or predecessors. At the beginning of the flowering season the illegitimate foragers often visited the front of the flowers before moving to the spurs; later, most queens quickly learned to land directly on the spurs. Even the 59.7% of plants that were visited only by illegitimate foragers set seeds. Close observation confirmed that the illegitimate foragers opened the inner petals enclosing anthers and stigma frequently when visiting the front of the flowers before robbing, or occasionally when walking about on the flowers or collecting nectar through the perforated spurs.