A euphemism for sex education, especially when taught informally. For example, It's time Father told the children about the birds and the bees. Cole Porter alluded to this expression in his witty song, "Let's Do It, Let's Fall in Love," (1928) when he noted that birds, bees, even educated fleas fall in love. This idiom alludes to sexual behavior in animals to avoid explicit explanation of human behavior. [Second half of 1800s]