The subject of a hit song in 1972, the red back spider is very common in Australia. You can find it under your bike seat, table or, as here, under the rainwater tank or in the top of your watering can. Today it can also be found in Becky’s squares.
In the song, the singer is bitten on his bottom, because he didn’t see the spider on the toilet seat.
The red back bite can be lethal, but not commonly to adults. The song was a joke, really, full of colloquialisms.