"There Was Once an Old Lady Who Swallowed a Fly" (alternatively "I Know an Old Lady Who Swallowed a Fly"', "There Was an Old Woman Who Swallowed a Fly" or "I Know an Old Woman Who Swallowed a Fly") is a children's song with a cumulative structure. The tune was written by Alan Mills, and the lyrics were penned by Rose Bonne. Probably the best-known version of the song was released on Brunswick Records in 1953, and sung by Burl Ives.
The song tells the story of an old woman who swallowed increasingly large animals, each to catch the previously swallowed animal. There are many variations of phrasing in the lyrics, especially for the description of swallowing each animal. The spider and fly are described each verse, but the other animals are only described when they are introduced. The joke of the song comes from the fact that the woman clearly should have died after swallowing the bird, but manages to swallow even more animals of ridiculous sizes with no problem and survives, and yet she suddenly dies after swallowing a horse (which is not much larger than the donkey she swallows and possibly even smaller than the cow she swallowed earlier).
In some versions, "perhaps she'll die" is replaced with "don't ask me why". Also, "she died of course" is replaced with "of course, of course, she swallowed a horse", leading to yet another cumulative verse that ends the tale.
An Arthur episode is called "Emily swallows a horse", in which the song is used as an analogy for the increasingly complex and incredible lies that the character must use to cover her original falsehood.
The lyrics form part of the theme song for the popular children's show Round the Twist.
^"Songs with Pictures" by M.B.K., Chicago Daily Tribune, November 12, 1961, page E34. (Reviewing a children's picture book, I Know an Old Lady illustrated by Abner Graboff of the music and lyrics of the song)