Bug, Insect, Creepy Crawly
noun
The kanji and the word are exactly the same. That means they share meanings as well. This word is actually more general than the English words insect and bug, though. It covers things like worms and spiders, too, so in that sense it's more like creepy-crawly.
むし
Since this word is made up of a single kanji, it should use the kun'yomi reading, which is also the reading you learned when you learned this kanji!
あ、虫がいる！
Oh, there's a bug!
あの虫、口から白い糸をはいているよ！
That insect is spinning white thread from its mouth.
とても大人しい虫だけど、ペットにはできないよ。
It's a pretty obedient insect, but you can't have it as a pet.