Translation

imo-mushi means "Caterpillar" in English.

imo-mushi written with kanji is 芋虫.
These are jouyou kanji 常用漢字, taught in junior high, chuugakkou 中学校.
imo-mushi written with katakana is イモムシ.
imo-mushi written with hiragana is いもむし.
Romaji i mo mu shi
Hiraganaいもむし
Katakanaイモムシ
Kanji 芋 虫
Meaning Potato Bug
School Level 中 小1

Further Reading

Wikipedia: イモムシ (Caterpillar)