Phylogeny: The question of ‘phylogeny’ or ‘evolution’ describes the evolutionary history of the behavior and how the behavior has come to be today.

Though the potential benefits and costs of sexual cannibalism are most frequently studied in the explanation for the behaviors widespread occurrence among arthropods, several related traits shared among sexually cannibalizing species can begin to explain why sexual cannibalism occurs in the species that it does.

Several traits are common to taxa of animals engaging in sexual cannibalism, including the following:

Comparison among the predatory species that participate in sexual cannibalism shows trends of increasing frequencies of cannibalism in mating in species that rely on predatory behavior over other foraging behaviors. For example, the highly predatory H. helluo and P. milvina strains of the wolf spider demonstrate this trend as H. helluo show cannibalism in about 30% of matings while P. milvina does so in about 1% of matings(Wilder et al 2009). These species have evolved to obtain specific food sources through adaptations like venom and body parts specialized for predation. These same adaptations are involed in sexual cannibalism, suggesting that predatory behavior might precede sexual cannibalism in evolutionary time.

Pictured: Extreme sexual size dimorphism in wolf spiders.
Females are shown on left with 10 mm scale bars (Logunov 2011)

Invertebrates, including arthropods, tend to show sexual size dimorphism with females as the larger sex. The frequency of this female-favored size ratio in the phylum could represent a correlation between sexual cannibalism and physically superior females. Study of the wolf spider species S. ocreata shows the highest frequency of sexual cannibalism by females in the largest females and the smallest males (Person & Uetz 2005). This suggests that perhaps this evolved ratio gives females the physical advantage necessary to complete cannibalism in mating with minimal risk of harm to themselves.

The morphology of sexually cannibalizing species (specifically the internal insemination often required) forces the males of the species to assume vulnerable positions in order to successfully complete fertilization. For example, in many spiders, both sexes have genitalia on their dorsal surfaces which must come into close contact during mating (Wilder et al 2009). As a victim of predation, the male’s morphology is limiting and aids the process of sexual cannibalism. Also, studies of the evolution of the male praying mantis genitalia suggest that the rapid evolution of certain genital traits may be the result of the selective pressures of sexual cannibalism in the species (Jensen et al 2009).