What was the name of bug used in Harry Potter and Goblet Fire?

The bug used in Harry Potter and the Goblet of Fire is called a Blast-Ended Skrewt. It was a cross-breed of a manticore and a fire crab, created by Professor Firenze for his Defence Against the Dark Arts class.

It's important to note that the Skrewt is more of a creature than a bug, but the term "bug" was sometimes used to describe it informally in the book and movie.