1A general term for small animals such as insects (e.g. mosquitoes, moths, crickets).
夏になるとベランダに虫がよく来る。
In summer, insects often come onto the balcony.
蛍は夜に光る美しい虫だ。
Fireflies are beautiful insects that glow at night.
庭の花が虫に食べられてしまった。
The flowers in the garden were eaten by bugs.
2Worms such as earthworms or roundworms; elongated, soft-bodied invertebrates (including parasitic worms in some contexts).
釣りの餌にミミズという虫を使う。
Worms called 'mimizu' are used as bait for fishing.
下痢がひどくて、医者は寄生虫が原因かもしれないと言った。
The diarrhea was bad, and the doctor said it might be caused by parasites (worms).
3From a traditional belief in an internal 'insect' thought to influence one's mind and feelings; used figuratively for an unconscious impulse or sudden inner urge.
彼は理由もなく旅に出た。虫が騒いだのだろう。
He left on a trip for no apparent reason. Perhaps an inner urge stirred him.
昔は原因不明の病気を『虫のせい』と言うことがあった。
In the past, people would sometimes blame an unexplained illness on 'an insect inside them.'
4Restlessness or fretfulness; often used to describe a baby or young child being fussy or unsettled, traditionally blamed on an inner 'insect.'
赤ちゃんが虫でぐずって、なかなか眠ってくれない。
The baby is fretful and fussy, and won't easily fall asleep.
試験前はいつも虫がおさまらず、そわそわしてしまう。
Before an exam, I'm always fretful and can't sit still.
5A person deeply devoted to one thing; usually attached after another noun to indicate an enthusiast (e.g. 'bookworm').
彼は本の虫で、休みの日は一日中読書している。
He's a bookworm; he spends his days off reading all day.
彼女は仕事の虫と呼ばれるほど働き者だ。
She's such a hard worker that people call her a 'work bug.'
6A valve core (the removable part of a tire valve used for inflation) — colloquially called 'mushi' in some contexts.
自転車の空気が抜けていた。虫が壊れているらしい。
The bicycle tire had lost air. It seems the valve core is broken.
タイヤの虫を交換してもらったら空気がちゃんと入った。
After having the tire's valve core replaced, the air held properly.
7In hanafuda (Japanese playing cards), 'mushi' is a particular winning combination used in the game; usually written in kana.
花札でむしを取って高い役を目指す。
In hanafuda, you try to capture 'mushi' cards to aim for a high-scoring hand.
ルールによってはむしが強い役になることもある。
Depending on the rules, 'mushi' can be a strong hand.