He is one of the increasingly rare Thamnophis species, also known as a Ribbon Snake or Garter snake. Throughout the US, many folks refer to them also as 'grass snakes' although generally that name is reserved for Natrix sp. which have only small lines near the head, and no lateral lines down the body.
There are 12 species of rattlesnake in the US, and 9 are found in Texas. There are a total of 15 subspecies of venomous snakes in Texas, and they are all easily identifiable. 14 of them are pit vipers, and the other is the coral snake. You can recognize pit vipers by their triangular head, pits in the face, and vertically split pupils. (notice the very round pupils of our garter snake friend there). Coral snakes are also easy to identify by their warning bands of red, yellow and black. (they're also quite shy, it's quite rare that you would ever get to see one)
Here is a little more info about the poisonous snakes in Texas and how to identify them and what to do in the case of snakebite:
http://www.tpwd.state.tx.us/expltx/jrna ... opperheads