They are out of print, but I would also suggest David Gerrold's War Against the Chtorr series. The series is unlikely to be finished - David is now 72 - but the books are really, really thought provoking. The 3rd book is..traumatizing on many levels, but, again, very thought provoking.

Gerold is famous for, when as a young man, he wrote the famous original series Star Trek episode entitled "The Trouble with Tribbles."

That said, the War Against the Chtorr, is not a happy tail. It's dark, really dark, but you might call it a dark purple. Or crimson.

Read the books and you'll understand why.

Again, for that third book, keep something that keeps you mellow nearby. And, at least for me, I had to take sips of that book's prose the first time. Even now...oy.