I can't think of any. They are close synonyms. "Ridiculous" is a more common, everyday word. "Ridiculous" literally means inviting ridicule. Ridicule is mockery or scorn. I'm sure that the Spanish cognate "ridículo" is similar. "Ludicrous" literally means inviting laughter--insulting, mocking laughter.

That's a great question! They both mean something so foolish that it invites laughter, and they can almost be used interchangeably but there are differences. "Ludicrous" is almost always used in a negative connotation, while "ridiculous" can be used positively. See examples below: 1. Because John is too lazy to work, his ideas of becoming a billionaire are ludicrous. (negative) 2. I laughed so much at the comedy show because the comic was ridiculously funny. (positive) By the way, if you're interested in discussing more subtle differences like this in the English lesson or you want an TEFL certified English teacher to practice having conversations with, I would be happy to work with you! I currently have some openings in my schedule! https://teach.italki.com/teacher/5129645