'armyworm' originates from English, specifically a compound of 'army' and 'worm', where 'army' referred to a massed group and 'worm' meant a creeping insect or larva.

'armyworm' developed as a compound in modern English (from around the 19th century usage) combining 'army' + 'worm'; 'worm' itself comes from Old English 'wyrm' meaning 'serpent' or 'creeping thing'.

Initially the elements meant 'a massed group' and 'a creeping insect'; over time the compound came to denote specifically the larval pests that march in groups and damage crops.