Male vulnerability explains the occurrence of sexual cannibalism in a moderately sexually dimorphic wolf spider

• We measured proximate causes and fitness benefits of sexual cannibalism in a moderately sexually dimorphic wolf spider.
• Randomly paired and laboratory-matured females frequently attacked males following mating and relatively smaller males were at higher risk.
• Relatively older males were less likely to avoid female attacks.
• Sexual cannibalism affected positively female fitness independent on the female size, condition and foraging rate.
• Male vulnerability mediates the occurrence of sexual cannibalism in Hogna radiata females.

Sexual cannibalism is a widespread phenomenon among a few animal taxa. Its occurrence is interpreted as female and/or male optimal reproductive decisions or as a non-adaptive side effect of selection for efficiently foraging females. In spite of the amount of research addressed at understanding its evolutionary origins, we lack accurate information about the proximate causes of sexual cannibalism. In a moderately sexually dimorphic wolf spider (Hogna radiata, Araneae, Lycosidae) we assessed the factors mediating the occurrence of sexual cannibalism and its fitness benefits to females. Sexual cannibalism was a rather common outcome of laboratory mating interactions, occurring in more than a quarter percent of courtship interactions involving virgin females. Sexual cannibalism mostly followed mating. Occurrence of sexual cannibalism depended on male vulnerability to female attacks: relatively smaller males were at higher risk of being attacked and older males were less likely to avoid female attacks. Sexual cannibalism had direct and positive effects on female fitness, as sexually cannibalistic females exhibited increased fecundity irrespective of their size, condition and foraging rate. Male consumption was almost complete and represented a relevant food intake to females. We interpret sexual cannibalism as a strategic foraging decision for H. radiata females that adjust their aggressive behaviour towards males so as to limit its potential costs.