Red and black, venom lack is the official south Texas version.
Copperheads? I know they're around Cuero in DeWitt County; never saw one around Austin, and certainly not out here in the desert.
Wooded areas in the eastern half of Texas have copperheads. We don't have many down here on the middle coast where my property is at and the big tree is scrub oak or mesquite or huisache, but just a little inland in the post oak/live oak, they abound. I grew up south of Houston in Brazoria County, lots of 'em back in the woods there. Their poison isn't that bad, never heard of anyone being killed by one, but getting bit by one ain't exactly fun from what I hear and is to be avoided. Not as many rattlers where I grew up and they're everywhere you step down here. I think I'd trade the rattlers for copperheads. Plenty of moccasins both areas as both are wet.
As I understand it, there's only one moccasin, well, cottonmouth anyway. All those yellow/black and different versions of water snakes that are non-poisonous are of a different genus,
Natrix. They get big, are nasty looking, can infest a pond or tank, and can be very aggressive, but have no venom. They're mean son of a guns, though, will come after you upon slightest provocation and test how confident you are in your snake identification, ROFL! Been there, done that. Lots of the
Natrix are blotchy colored or patterned and are easily identifiable as not being a moccasin. However, there's about a bazillion species and if they're coming at you such that you can't see the head well enough to identify it as a pit viper, I just shoot first and ask questions later. ROFL!
http://www.hlasek.com/natrix_natrix_4197.html