A comparative analysis of the venom alkaloids produced by ants in the genusMonomorium (= Chelaner) collected on North Island and South Island, New Zealand, has been undertaken. All of the ants producetrans-2, 5-dialkylpyrrolidines along with 3,5-dialkylpyrrolizidines. The structures and sterochemistry of the novel alkaloidstrans-2-butyl-5-(8-nonenyl) pyrrolidine, (5E,8Z)-3,5-di(5-hexenyl)pyrrolizidine, and (5Z,8E)-3-methyl-5-(8-nonenyl)pyrrolizidine were established by unambiguous synthesis. The geographic distribution and the chemotaxonomic significance of the alkaloids produced by these ants are discussed.