The phenomenon of male spiders dying after mating is a common aspect of spider biology. This behavior, observed across numerous species, is curious due to its self-sacrificial nature. While not universal, this post-mating demise exemplifies complex reproductive strategies shaped by evolution. Understanding this reveals intricate interactions between sexes.
How Male Spiders Perish After Mating
Male spiders perish after mating through various mechanisms, most prominently sexual cannibalism. In many species, the female consumes the male immediately or shortly after copulation. For instance, the male Australian redback spider (Latrodectus hasselti) actively “somersaults” onto the female’s fangs during mating, with over 60% being eaten. This act provides the female with a nutritional resource.
Beyond cannibalism, some male spiders die due to the physiological cost of mating, experiencing extreme energetic exhaustion. The male dark fishing spider (Dolomedes tenebrosus) provides an example, where males die spontaneously after a single mating. Their death is linked to the expansion of their pedipalps, used for sperm transfer, leading to shriveling and cessation of heartbeat within minutes.
In other instances, a male spider’s death after mating may simply coincide with its natural lifespan. Many male spiders have significantly shorter adult lifespans than females, often lasting only months. Their adult phase is primarily dedicated to finding a mate, often at the expense of feeding. This contributes to their naturally brief existence. Thus, post-mating death can be a natural conclusion to their life cycle.
Why Post-Mating Death Persists
The persistence of post-mating male death in spiders is attributed to several evolutionary explanations, centered on maximizing genetic legacy. One reason is paternal investment, where the male’s body serves as a nutritional resource for the female. This sustenance can increase the female’s reproductive success, leading to more, larger, or healthier offspring. For example, studies on orb-web spiders show that female consumption of males results in healthier offspring and larger egg cases.
This self-sacrifice ensures the successful fertilization and development of the male’s offspring, particularly if his chances of mating multiple times are low. The Australian redback spider’s active self-sacrifice increases paternity compared to males that avoid cannibalism. By providing a substantial meal, the male enhances the survival prospects of his genes through his progeny.
Another advantage relates to mate guarding. In some species, the male’s death or physical presence, even as a consumed body, can prevent the female from mating with other males. For instance, a detached pedipalp, the male’s sperm-transferring organ, can act as a mating plug, blocking the female’s genital opening and reducing sperm competition from subsequent mates. This mechanism ensures the deceased male’s paternity. Female spiders often play a role, sometimes actively initiating cannibalism or selecting mates based on factors that may lead to the male’s demise.
When Male Spiders Survive
While post-mating death is a notable phenomenon, not all male spiders perish after copulation. The survival rate varies significantly across species, with many males successfully escaping or avoiding cannibalism. This diversity highlights a range of strategies males have evolved to ensure their survival and potential for multiple matings.
Male spiders employ various evasive maneuvers to avoid consumption by their mates. Some male communal orb-weaving spiders (Philoponella prominens) use a rapid catapulting mechanism, flinging themselves away from the female at speeds up to 88 centimeters per second immediately after mating. Other species, like the nursery web spider (Pisaurina mira), use silk to restrain the female’s legs during copulation, immobilizing her, allowing the male to escape. Some males even present the female with a “nuptial gift” of wrapped prey, distracting her during mating.
In some cases, males exhibit behaviors that reduce the risk of cannibalism by mating with less dangerous females. Certain widow spider males (Latrodectus hasselti and Latrodacteus geometricus) mate with sexually immature females, as they have not yet developed the strong predatory instincts of mature females. Additionally, some tarantula species have evolved exceptionally long pedipalps, allowing them to transfer sperm from a greater distance, reducing physical proximity to a potentially aggressive female. These varied adaptations demonstrate the complex evolutionary arms race between male survival and female reproductive needs.