hornworm; hairless caterpillar
Refers to a caterpillar without prominent hairs, especially the larva of hawk moths (Sphingidae). Often used for the green, fleshy caterpillars found on plants like sweet potato or tomato.
See also: スズメガ
There was a big hornworm on the tomato plant in the garden.
Imomushi refers to hairless caterpillars.
毛虫 refers to caterpillars covered in noticeable hair or bristles, while 芋虫 refers to smooth, hairless caterpillars, so the two are often confused as generic 'caterpillar'.
Katakana spelling is common; usually written in kana.
Hiragana spelling is also used, especially in children's contexts.
Kanji spelling is less common but still encountered.
Compound of 芋 (imo, 'potato, tuber') and 虫 (mushi, 'insect, worm'), from the caterpillar's resemblance to a potato or its association with tuber plants.