Sexual Cannibalism

"The reproductive interests of males and females rarely coincide" (Schneider and Lubin 1996).

Sexual cannibalism, the killing and consuming of potential or actual mating partners (Schneider and Lubin 1996), is a dramatic behavior that begs an explanation. How can an action that results in the death of a conspecific and potential mate be evolutionarily favorable? In the case of pre-copulation cannibalism, how can traits that allow an animal to be eaten before it can reproduce persist over evolutionary time?

While sexual cannibalism is relatively uncommon compared to other types of cannibalism, it is occurs in a wide spread of invertebrates, from gastropods to many species of arachnids (Elgar and Crespi 129). Sexual cannibalism has been observed during courtship, during copulation, and shortly after copulation (Elgar and Crespi 128).  

One theory to explain post- insemination sexual cannibalism is that males who are eaten gain higher paternity. This could be because copulation lasts longer and they are more likely to successfully fertilize eggs, or because they provide nutrition to the mother (Schneider and Lubin 1996, Elgar and Crespi 140-141). Experiments with the garden spider Araneus diadematus have shown that females who eat a single male significantly increase their body weight, which increases her fecundity (Elgar and Nash 1988).

While sexual cannibalism is relatively uncommon compared to other types of cannibalism, it is occurs in a wide spread of invertebrates, from gastropods to many species of arachnids. Sexual cannibalism has been observed during courtship, during copulation, and shortly after copulation (Elgar and Crespi 128).  
RedbackRedback Spiders
Male redback spiders take sexual cannibalism to the extreme, essentially committing suicide to feed themselves to their mates. During copulation, males somersault themselves onto the fangs of the female, and remain in this position until they are eaten, which depends on the hunger level of the female. Males benefit from this sacrificial behavior because males who are consumed mate longer, which leads to increased paternity. Cannibalism of one male also decreases the chances that the female will remate. Considering that males are unlikely to mate again even if they survive one mating experience, the paternity advantages of cannibalism overshadow the costs of suicide (Andrade 1996).