"The birds and the bees" (sometimes expanded to "the birds, the bees and the butterflies") is an English-language idiomatic expression which refers to courtship and sex, and is usually used in reference to teaching someone, often a young child, about sex and pregnancy. The phrase is evocative of the metaphors and euphemisms often used to avoid speaking openly and technically about the subject.
According to tradition, the birds and the bees is a metaphorical story sometimes told to children in an attempt to explain the mechanics and consequence of sexual intercourse through reference to easily observed natural events such as plant pollination.
The idiom could date back as far as Shakespeare, from these lines in Act 4, Scene 6 of King Lear:
Thou shalt not die. Die for adultery? No.
The wren goes to't, and the small gilded fly
Does lecher in my sight"
Here, Lear is talking to Gloucester about adultery, telling him that he must not fear being punished for it, as animals do it all the time and it is therefore a natural phenomenon. The link with the second line and the modern day idiom seems to fit, as both regard the subject of copulation, and particularly, copulation in nature. In this case, the wren represents the birds, whilst the "gilded fly" may refer to bees; which seem to be flies "gilded" with gold stripes.
