Alternatives to "break a butterfly on a wheel"

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"?

There's a whole range of answers concocted in a veritable arms race:

That's like using a hammer to kill a ladybug
That's like using a sledgehammer to kill a fly
That's like using a pistol to kill a cockroach
That's like using a shotgun to kill a mosquito!
That's like using a bazooka to kill a flea.
That's like using a cannon to kill a mosquito
That's like using a nuclear bomb to kill a mosquito

Where the butterfly on the wheel goes in that list is unclear- maybe between the sledgehammer and the pistol.

The figurative language surrounding this concept is generally pretty disturbing: to beat a dead horse, for example. The verb 'belabor' is nice, boring, alternative -- there is the expression 'to belabor the point.'