Giant Garter Snake – Thamnophis gigas

Giant Garter Snake – Thamnophis gigas – Brief Article

LaRee Brosseau

The giant garter snake, a non-venomous species listed as threatened, has been studied on Colusa National Wildlife Refuge (NWR) in California since 1996. Refuge staff and the U.S. Geological Survey’s Biological Resources Division field station in Dixon are using radio telemetry and mark recapture techniques to study the garter snake’s habitat use in relation to wetland restoration. A non-native species, the bullfrog (Rana catesbeiana), is a suspected predator of young garter snakes. Bullfrogs were collected for a pilot study examining the effects of introduced predators on snake populations.

Biologists closely observed radio-marked garter snakes to determine when the females were beginning to give birth and scheduled bullfrog collection to coincide with this period. Thirty bullfrogs were collected from late July to early August of 2000. Each frog was measured, sexed, and examined for stomach contents. In addition to numerous crayfish and invertebrates, two of the frogs had consumed small garter snakes. The frogs that had consumed the young snakes were among the smallest frogs collected. The Service hopes to further investigate the relationship between the non-native bullfrogs and the garter snakes within the Central Valley region.


Submitted by LaRee Brosseau of the Service’s Portland, Oregon, Regional Office.

COPYRIGHT 2000 U.S. Fish & Wildlife Service

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