When a flower is visited, a honey bee can understand if the nectar of that flower has previously been consumed by another bee, and leaves the flower immediately. This way, it saves both time and energy. Well, how does the bee understand, without checking the flower, that the nectar is consumed?
This is made possible thanks to the bees which have visited the flower earlier and marked it by leaving a drop with a special scent. Whenever a new bee looks in on the same flower, it realizes the scent, understands that the flower if of no use and goes on flying directly towards another flower. Thus, bees are not allowed to waste time on the same flower.
"Then to eat of all the produce (of the earth), and find with skill the spacious paths of its Lord: there issues from within their bodies a drink of varying colours, wherein is healing for men: verily in this is a Sign for those who give thought." (Surat an-Nahl (The Bee) 69)
"And He has subjected to you, as from Him, all that is in the heavens and on earth: Behold, in that are Signs indeed for those who reflect." (Surat al-Jathiya (Crouching), 13)