Brown tree snakes (Boiga irregularis) have become a serious threat to the endemic fauna (and flora, because they eat pollinators) of Guam. At least two pythons (Python molurus and Python bivittatus) and the Boa constrictor threaten to become a serious problem in southern Florida. And, now it appears that California has invasive water snakes of the genus Nerodia, possibly three species. Machado Lake, at the Kenneth Malloy Memorial Park, in Harbor City, Los Angeles County; the Folsom area of Sacramento County; and the Lafayette Reservoir, east of Berkeley have been reported to have non-native Nerodia populations.The Lafayette Reservoir has been known to have Diamond-back Water Snakes (Nerodia rhombifera) since the 1990's, and while the population seemed to go into decline it has been suggested that the population may be recovering. Since January of 2008, all non-native water snakes (genus Nerodia) are regulated as restricted animals by the California Department of Fish and Game (Sec. 671, Title 14, Calif. Code of Regulations). Thus, it is now unlawful to import, transport, or possess water snakes of the genus Nerodia in California without a permit. The founders of these populations are believed to be released pets since the snakes were available for many years in pet shops.
Concern for the invasive populations is based on the fact that they will compete with native snakes for food, and potentially decimate native fish populations.However, it seems more likely that they will alter the community composition of the local fish populations. The Machado Lake site is estimated to house 3000 non-native Banded Watersnakes, Nerodia fasciata pictiventris. But, it also contains other non-native species, including Koi and probably goldfish. Therefore, one non-native species may increase its population size by feeding on another non-native species; but in the process, also feed on the less common native fish and reduce their populations or push them into extinction.
Balfour, P. S., and E. W. Stitt. 2002. Geographic distribution: Nerodia fasciata fasciata (banded watersnake). USA: California: Sacramento Co. Herpetological Review 33:150.
Balfour, P.S., E.W. Stitt, and M.M. Fuller. 2007. Nerodia fasciata pictiventris (Florida water snake). Herpetological Review 38:363. (Provides updated information on populations found in Northern and Southern California).
Fuller, M.M. and B.W. Trevett. 2006. Nerodia fasciata pictiventris (Florida water snake). Herpetological Review 37:363. (First published record for the Florida water snake population in California).
Stitt, E.W., P.S. Balfour, T. Luckau, and T.E. Edwards. 2005. The southern watersnake (Nerodia fasciata) in Folsom, California: history, population attributes, and relation to other introduced watersnake in North America. Final report to US Fish and Wildlife Service. ECORP Consulting Inc.
