ladybug (n.)

also lady-bug, 1690s, from lady + bug (n.). The "lady" is the Virgin Mary (compare German cognate Marienkäfer). In Britain, usually ladybird or lady-bird (1670s), supposedly through aversion to the word bug due to overtones of sodomy, however this seems to be the older form of the word. Also known 17c.-18c. as lady-cow or lady-fly.