The phrase "busy as a bee" is used to describe someone who is very active and industrious. The origin of this phrase is deeply rooted in the observation of bee behavior and has been used in literature for centuries. 

Bees are known for their hard work and diligence, constantly gathering nectar, producing honey, and maintaining the hive. This industrious behavior has made them a symbol of hard work and productivity. 

One of the earliest known uses of the phrase appears in Geoffrey Chaucer's "The Canterbury Tales," written in the late 14th century. Chaucer writes, "In wommen been...busy as bees," highlighting the industrious nature of women by comparing them to bees. William Shakespeare also used the imagery of busy bees in his play "Henry V," written in the late 16th century. 

In Act 1, Scene 2, the Archbishop of Canterbury describes bees as "creatures that by a rule in nature teach the act of order to a peopled kingdom," emphasizing their busy and organized nature.