Buff-tailed Bumblebee queen (Bombus terrestris)

Buff-tailed Bumblebee queen (Bombus terrestris), with mites. 
 

Newly emerged queen Buff-tailed Bumblebee (Bombus terrestris) - my first of the year. (Also the first Small Tortoiseshell and Red Admiral butterflies on this sunny afternoon.) It is quite common for newly emerged queen bumblebees to carry quite a heavy cargo of mites. Unlike the parasitic Verroa mite of honeybees, these are commensal mites which have been eating the crud in the nest over the winter. The go along with the queen for a ride and drop off on flowers when she stops for a feed, only to hitch a lift to a new nest on a later bee host.

So answer me this. How big is the brain in these mites? How do they mange to figure all that out?