theres actually been proof of some of them not man made, the earth releasing a type of thing i can't remember the name of, and real crop circles are magnetic, and exceptionally high in energies and vibrations and such.

maybe it's just natures way of confusing us, and nature is really laughing its *** off. i mean seriously, have you taken a look at some of the amazing things nature can do, like those amazing trees, and creepy plants, and odd things, and have you ever spoken to the spirits of the land? They don't necessarily believe we are intelligent beings, and tend to lecture us and give us some great advice.
i wouldn't be surprised if it's just the earth doing it. i don't much gravitate towards ufos landing there. if you think it's spirits, remember the earth is also a living entity spirit, that would like to communicate to us.