Bumblebees: using all the senses

Sight, sound and smell are all needed 

 to track down bumblebees in September. 

On windy days like today bee flight can seem erratic. Even if you catch sight of a bee it can rapidly disappear.
   Listening to the buzz may help you to tell wasps, flies and bumblebees apart. The tone of a bumblebee is deeper and by listening carefully you can work out the bee's speed and direction. There are probably differences in tone between bumblebees that would help you identify which bee it is.
  Smell is helpful too in noticing when flowers are producing nectar. Stand by a fruiting ivy in September and you can smell the nectar on the leeward side [the opposite side to the wind].
Yellow Corydalis is a self-sown plant [also known as a weed] attracting bees during mild weather in mid-September:

On mild windy days, yellow corydalis which grows beside walls offers a source of nectar that's less blown about.

The other reliable fall back for bumblebees in rain is white deadnettle:

which seems to provide nectar even on windy and wet days:

Maybe it's more productive than clover and scabious which don't seem to be visited as often in September.