Ahhh cool! Although I was born in Texas, I have lived most of my life in Georgia and most of my herping has been limited to the South Eastern States. I did a quick search on Texas ssp of gartersnakes before I posted before and failed to notice that there are 2 ssp of blackneck garters. "Thamnophis cyrtopsis cyrtopsis" is the black neck I looked at before and it has a yellow dorsal stripe so I dismissed looking any further. The eastern black neck "Thamnophis cyrtopsis ocellatus" is a closer match and also the only of the 3 mentioned species that range into the San Antonio area. Western Plains garters aren't even close. They are found in the extreme northern part of Texas in that little square part west of Oklahoma whatever that's called.
Thamnophis cyrtopsis ocellatus
Also...that particular species feeds heavily on frogs so while bug belly is unlikely...frog belly is possible...so it may or may not be gravid afterall.
