In most animal species males can increase their fitness by mating with several females (sperm is relatively cheap to produce and male reproductive success is, unlike that of females, generally not limited by the number of gametes they produce). Most mating systems are accordingly characterized by males that mate with multiple females and that exhibit a high variance in reproductive success. However, in several insect and spider species males mate with only one female - in the absence of any paternal care provided. In such species males often make a terminal mating investment by emasculating themselves (leaving parts of their copulatory organs behind in the females copulatory tract) or by sacrificing themselves by offering themselves as a meal to the females or by simply dying in copula. The benefits of such a terminal investment appears to be the avoidance of sperm competition with ejaculates from other males by plugging the female and/or reducing the female’s propensity to mate again.