WordNet sense 1 (harmless European snake with a bright yellow collar; common in England):

Natrix natrix, ring snake, ringed snake

WordNet sense 2 (any of numerous nonvenomous longitudinally-striped viviparous North American and Central American snakes):

garter snake

WordNet sense 3 (either of two North American chiefly insectivorous snakes that are green in color):

green snake