Occurred to me recently to wonder about the word cooties.
According to Wikipedia:
“The word [cooties] is thought to originate from the Austronesian language family, in which the Philippine languages, Maori and Malaysian-Indonesian word kutu refers to a parasitic biting insect. The earliest recorded uses of the term in English are by British soldiers during the First World War to refer to lice that proliferated in battlefield trenches.”
(This is one of those cases where both etymology and entomology are relevant.)
A related Wikipedia article also notes, perceptively, that “Among children, the word effectively serves as a device for enforcing separation of the sexes.”