noun
cutworm
Refers to the larvae of certain moths (especially Noctuidae) that cut through plant stems at ground level, often damaging crops.
根切り虫が野菜の苗を食い荒らした。
Cutworms ate up the vegetable seedlings.
Compound of 根切り (nekiri, 'root cutting') + 虫 (mushi, 'insect'). The derivation is straightforward from the components.