Alternatives to "break a butterfly on a wheel" [duplicate]
Use a sledgehammer to crack a nut.
to do something with more force than is necessary to achieve the result you want
When he sent ten men to arrest one small boy, he clearly used a sledgehammer to crack a nut.
Better yet: Use a sledgehammer to swat a fly!
idioms.thefreedictionary.com
Heavy-handed?
http://www.usingenglish.com/reference/idioms/heavy-handed.html
If someone is heavy-handed, they are insensitive and use excessive force or authority when dealing with a problem.
In other words, I love the Chinese idiom with a similar meaning:
用高射炮打蚊子(literally: to shoot a mosquito with an anti-aircraft gun)
Overkill is the phrase that comes to mind here. But if you're looking for a colorful animal metaphor, maybe "beat a dead mouse"?