Traditional Nursery Rhyme
Farmer's knew of the Ladybird's value in reducing the level of pests in their crops and it was traditional for them to cry out the rhyme before they burnt their fields following harvests (thus reduced the level of insects and pests).
The English word ladybird is a derivative of the Catholic term "Our Lady". The tradition of calling this rhyme was believed to have been used as a seemingly innocent warning cry to Catholic (recusants) who refused to attend Protestant services as required by the Act of Conformity (1559 & 1662). The law forbade priests to say Mass and forbade communicants to attend it. Consequently Mass was held secretly in the open fields. Laymen were subject to jail and heavy fines and priests to execution. Many priests were executed by the terrible death of being burnt alive at the stake or, even worse, being hung, drawn and quartered. The most famous English recusants were Guy Fawkes and the Gunpowder Plot Conspirators.
It is possible that the word Ladybird was exchanged for Ladybug, in the American version of the nursery rhyme, due to the word association with Firebug meaning an arsonist or pyromaniac. There has been some speculation that this Nursery Rhyme originates from the time of the Great Fire of London in 1666.
Thank you, Rita, for my precious ladybug dip bowl and little knife.