How mating affects male lifespan is poorly understood. Using single worm lifespan assays, we discovered that males live significantly shorter after mating in both androdioecious (male and hermaphroditic) and gonochoristic (male and female) Caenorhabditis. Germline-dependent shrinking, glycogen loss, and ectopic expression of vitellogenins contribute to male post-mating lifespan reduction, which is conserved between the sexes. In addition to mating-induced lifespan decrease, worms are subject to killing by male pheromone-dependent toxicity. C. elegans males are the most sensitive, whereas C. remanei are immune, suggesting that males in androdioecious and gonochoristic species utilize male pheromone differently as a toxin or a chemical messenger. Our study reveals two mechanisms involved in male lifespan regulation: germline-dependent shrinking and death is the result of an unavoidable cost of reproduction and is evolutionarily conserved, whereas male pheromone-mediated killing provides a novel mechanism to cull the male population and ensure a return to the self-reproduction mode in androdioecious species. Our work highlights the importance of understanding the shared vs. sex- and species-specific mechanisms that regulate lifespan.