Two species of water snake have apparently been introduced to California. A new study published in PLOS ONE assesses the risk to native habitats and wildlife by identifying local habitat that would be suitable for the invasive species.
Water snakes are mainly found in the eastern half of North America: they come no further west than the eastern parts of Colorado and New Mexico. On the west coast their ecological niche is filled by large, aquatic garter snake species like the Sierra, giant and two-striped garter snakes (water snakes themselves can functionally be seen as large, aquatic garter snakes: fewer stripes, more attitude).
So how did water snakes establish themselves in California? The researchers attribute it to the release of captured pets. I’ve kept both of the species in question — northern (Nerodia sipedon) and banded (N. fasciata) water snakes — but water snakes are not all that popular among snake keepers. I’m amazed that enough snakes were kept in California that a sufficient fraction were able to escape or be released, and a sufficient fraction of that fraction were able to survive long enough to reproduce. Not that I’m saying it’s impossible, or even unlikely — if nothing else, water snakes are seriously r-selected, and can really pump out the babies — I’m just boggled by it.