I am Australian and have always known it exclusively as the American term “ladybug”. Never heard of ladybird before.
We call them ladybirds in the UK. No idea why.
Santa Maria is the lady in question. The bird part could be a corruption of ‘beetle’ maybe? Or perhaps just it just sounded more poetic.
Germany: Marienkäfer (Mary’s beetle)
France: la bete a bon Dieu (good God’s animal)
Russia: Bozhya korovka (God’s little cow)
Greece: paschalitsa (little Easter)
Portugal: joaninha (little Joanne)
Spain: mariquita (little Maria)
Wales: buwch goch gota (small red cow)
Scotland: daolag-bhreac (speckled beetle)
Slovenia: pikapolonica (spotty bug)
Argentina: Vaquita de San Antonio (St. Anthony’s small cow)
Stolen from https://www.nickybay.com/ladybird-beetles-brief-history-behind-name-lady/
Also Australian, never heard of ladybird… Weird