Slithering San Francisco Garter

By Keanna Harrison, Intern

The San Francisco garter snake (Thamnophis sirtalis tetrataenia) is a sub species of the common garter snake and is a rare species in itself. It is described as being “the most beautiful serpent in North America”, with its dominant reddish-orange head and pale yellow stripe washed with turquoise running down its back edged by red bands and broad black stripes. This subspecies is native to California but its range is limited to the San Francisco Peninsula southwards to the Santa Cruz Mountains. The typical habitat San Francisco garter snakes prefer are scattered wetlands and grasslands, which they use for camouflaging and hiding because they are highly active during the day.

The SF garter snake hunts in water that is 2 inches deep or less, and their average prey are California red-legged frogs (which happen to be federally listed as endangered), as well as juvenile bullfrogs, western toads, mosquito fish, and the toxic California newt. The female subspecies typically gives live birth from June to September averaging a litter size of 16 babies. The adult snakes can reach up to 3 feet in length.

San Francisco garter snakes are not a threat to humans but have toxins in their saliva that sting and are deadly to their prey. It will defend itself by discharging a foul smell from its anal glands and also empty its bowels on its captor. Sadly, the San Francisco garter snake remaining population is 1500. It was state listed as endangered on March 11, 1967 and federally listed in 1973 because of a decline in numbers due to agriculture, commercial, and urban development and illegal snake collecting in the last sixty years. Another factor impacting the subspecies population are bullfrogs preying on the juvenile snakes.


Photo from Wikipedia