Sperm transfer constraints are common phenomena in spider mating systems, influenced by both behavioral and morphological factors. Non-motile, encapsulated sperm cells must navigate through narrow male and female ducts during short (only seconds) copulations, all while under the pressure of female aggression, which can include sexual cannibalism and genital damage. However, little attention has been paid to the impact of male and female internal genital morphology on sperm transfer. In this study, we quantify the number of sperm transferred by males in five species of the genus Argiope as a direct measure of reproductive success. We explore sperm transfer in relation to copulation duration, sperm availability, sexual dimorphism, and female aggression. Additionally, we compare intra- and interspecific variation in sperm transfer by examining internal male and female genital morphological traits. Finally, we discuss the allometry of internal genital morphology in terms of sperm transfer in spiders. Our findings indicate that the occurrence of sexual cannibalism is the significant factor impacting sperm transfer in the genus Argiope. We observed a positive, albeit non-significant, correlation between sperm duct width and sperm transfer. Nonetheless, interspecific variability in allometry and methodological challenges underscore the need for continued research to fully understand the complexities of internal genital evolution in spiders.