Lyndon B. Johnson's wife, Claudia Taylor Johnson, was always known as Ladybird or Lady Bird; and if Wiki is correct, this came from her nurse - so it's American usage alongside of Ladybug. Article sez:

Though she was named for her mother's brother Claud, during her infancy her nurse commented, she was as "purty as a ladybird" which is a brightly colored beetle commonly known as a ladybug in the United States. That nickname virtually replaced her given name for the rest of her life.

Certainly sounds better than Lady Bug Johnson.