This was the first Who song written by their bass player, John Entwistle, who also sings on the track. The first Who album, My Generation, was written almost entirely by Pete Townshend, who wanted his bandmates to share the load on their next one, A Quick One. Their label was on board with this plan as well: to encourage them to write their own songs, they offered each member a £500 advance if they each wrote a song. Entwistle delivered "Boris The Spider," a song about a creepy, crawly spider that drops from the ceiling and meets a sticky end when he gets smashed with a book.
Entwistle was afraid of spiders as a kid. He wrote this about seeing a spider crawling from the ceiling and squishing it.
Entwistle wrote this as a joke, but it became a concert favorite. It is a fun song that offset many of the more serious Who songs.
This was the only song from the album that they continued to play live.
In the UK, the album was called A Quick One. It was changed to Happy Jack in the US to avoid being offensive.
After he wrote this, Entwistle started wearing a spider medallion at concerts.