The Stereotyped Behavior of Sexual Cannibalism in Latrodectus-Hasselti Thorell (Araneae, Theridiidae), the Australian Redback Spider

Abstract

This paper presents the first account of stereotyped behaviour in the practice of sexual cannibalism in any species. Cannibalism is achieved by female Latrodectus hasselti spiders, primarily because the copulatory orientation of the male in this species is unique and does not conform to the orthodox posture of males of other Latrodectus species. In this case, after penetration of the epigynum with one palpal embolus, the male turns a somersault through 180-degrees so that his abdomen comes to rest against the female's mouthparts, whereupon she begins to devour him. The cannibalistic process is slow and the male often succeeds in a second intromission with the other palp. The somersault is highly stereo-typed and predictable; it was observed in all 56 intromissions in the present study. The nuptial death risk to the male during copulation if both palps are employed is 0.66. However, even if he escapes copulatory demise he will die from his injuries within two days. Male Latrodectus hasselti can be mated with female L. katipo, an allopatric species native to New Zealand. Somersaulting by the male L. hasselti also occurs in this inter-specific copulation but the female L. katipo makes no attempt to devour him. It is concluded that male somersaults and female cannibalistic behaviour in L. hasselti are genetically programmed events.