noun
cabbageworm; caterpillar of the cabbage white butterfly
Specifically refers to the green caterpillar of the cabbage white butterfly (モンシロチョウ), often found on cabbage and related plants.
キャベツの葉に青虫がついていた。
There was a cabbageworm on the cabbage leaf.
青虫はモンシロチョウの幼虫だ。
The cabbageworm is the larva of the cabbage white butterfly.
Compound of 青 (ao, 'green') and 虫 (mushi, 'insect/worm'), literally 'green worm'. The exact historical derivation is uncertain, but the word has long been used for the green caterpillar of the cabbage white butterfly.