http://www.rcreptiles.com/blog/index...rawl-in-the-gr
I'm pretty sure the only thing you'd need to watch out for is ticks. I really doubt he 'licked' the grass, he was probably just flicking his tongue to smell, you know? Unless he was actively ingesting the dirt the grass is in, I seriously doubt parasites are likely, or even possible. (Although, yes, snakes can get internal parasites, but that's generally from infected prey items)
It's good to take precautions, but you don't have to keep him in a bubble. My advice? Calm down, and enjoy him. ^.^