The noun 虫子 (chóngzi) means "bug," "insect," or "worm." It is a colloquial term used in everyday speech to refer to small crawling or flying creatures. For example, 被虫子咬 means "bitten by a bug."
夏天的时候,房间里总有虫子飞来飞去。
Xiàtiān de shíhou, fángjiān lǐ zǒng yǒu chóngzi fēi lái fēi qù.
In summer, there are always insects flying around the room.
小朋友在草地上抓虫子玩。
Xiǎo péngyǒu zài cǎodì shàng zhuā chóngzi wán.
The children were catching insects on the grass for fun.
我昨晚被虫子咬了好几个包。
Wǒ zuówǎn bèi chóngzi yǎo le hǎo jǐ gè bāo.
I got bitten by insects several times last night.