Manual Growing lights
equipped with a blue hive door (in the visible spectrum for bumblebees) and
has a special, flower shaped, UV pattern around the entrance of the hive to help the [...] available for bumblebees to fly around, this shows that a lot of bumblebees can get lost.
Note: A bumblebee colony can lose all its foraging bees in just 2 [...] but to open the hive the following day. Never keep a
hive closed for longer than one day unless additional pollen is fed to the bees.
2.1 When to open