I don't have data, but would suspect that bots are different between FB and twitter: most bots on twitter that I've encountered are aimed at sending linkbait based on keywords. (That is, you send a tweet with a particular word in it, and you get back a tweet with some link the bot thinks you might be vulnerable to clicking on).
By contrast, bots on FB tend to harvest your personal data (friends, likes, etc) and apply that information to what you get hit with.
But again, my experience could be limited; I haven't confirmed it against any studies investigating the question properly. If someone has such a study available I would hope they'd provide a link from which we could all benefit.
