Photoshop.
This one was sort of a doozy. It's 6 inches wide by 5 feet tall. Everything was hand-drawn in Photoshop with a tablet, though I may have borrowed the beetles from *cough* a previous piece. I broke it into panels to upload so I could show some more details.
There may be some pretty blatant ecological discrepancies, but I won't say anything if you don't.