That sounds like "Rust" by Joseph E. Kelleam. You can find this story in Isaac Asimov Presents: The Golden Years of Science Fiction, edited by Asimov and Greenberg and published by Bonanza. The clumsy claws and inability to build new robots are a dead give away.
The protagonist is X-120:
He and his companions were highly developed robots, the last ever made by the Earthmen. X-120 consisted of a globe of metal, eight feet in diameter, mounted upon four many-jointed legs. At the top of this globe was a protuberance like a kaiser's helmet which caught and stored his power from the rays of the sun.
From the "face" of the globe two ghostly quartz eyes bulged. The globe was divided by a heavy band of metal at its middle, and from this band, at each side, extended a long arm ending in a powerful claw. This claw was like the pincers of a lobster and had been built to shear through metal. Four long cables, which served as auxiliary arms, were drawn up like springs against the body.
But never in all our years have we made a single robot that resembled ourselves.
I think the killed animal was a rabbit, not a butterfly.