The black widow spider (Latrodectus) is one of the most widely recognized arachnids globally, largely due to the female’s distinctive glossy black body and the bright red hourglass marking on her abdomen. This striking appearance is often overshadowed by the species’ infamous reputation concerning its reproductive life. The name “widow” has long been associated with the question of whether the female consistently consumes the male after mating. This behavior, while not universal, is a complex biological interaction that reveals much about the evolutionary pressures on both sexes.
The Reality of Sexual Cannibalism
Sexual cannibalism, the act of the female consuming the male before, during, or after copulation, is observed in several spider species, including some black widows. However, it is not the standard outcome across all species in the Latrodectus genus. The dramatic image of the female always devouring her mate is often exaggerated, partly because early observations were conducted in laboratory enclosures where males could not escape.
In the wild, many North American species, such as the Western Black Widow (Latrodectus hesperus), rarely exhibit this behavior. Conversely, in Southern Hemisphere species, like the Australian Redback Spider (Latrodectus hasselti), cannibalism is much more common. The female’s size, often outweighing the male by 10 to 160 times, also contributes to the possibility of the male being mistaken for prey.
The Black Widow Mating Process
The male black widow approaches the female with extreme caution, as his survival depends on signaling his identity as a mate rather than prey. Since the female is sedentary and relies on web vibrations to detect prey, the male must first navigate the sticky silk structure. He uses careful, species-specific vibrational patterns on the silk lines to announce his presence and distract the female from her predatory instincts.
The male also detects chemical signals (pheromones) on the female’s web to gauge her reproductive status. Sperm transfer involves the male using his pedipalps, small paired appendages near his mouthparts that function as secondary sexual organs. He charges these pedipalps with sperm and inserts them into the female’s paired genital openings for copulation. This delicate process must be completed while maintaining a safe distance from the female’s much larger body and fangs.
Biological Drivers for Female Aggression
When cannibalism occurs, it serves biological imperatives for both sexes. For the female, consuming the male provides a nutritional boost, which is converted into resources for egg production. This influx of protein and energy leads to larger, healthier clutches of eggs, increasing her reproductive success.
In some species, the male actively participates in his own consumption, a strategy known as “terminal investment” or self-sacrifice. For example, the Redback Spider male performs a copulatory somersault, placing his abdomen directly onto the female’s fangs. This self-sacrificial posture increases the duration of copulation, allowing the male to transfer more sperm. Furthermore, a female who consumes her first partner is more likely to reject subsequent mates, maximizing the first male’s paternity.
The Male’s Post-Mating Survival
Despite the species’ infamous name, a significant number of male black widows successfully complete the mating process and escape the web. These surviving males, particularly those of North American species, often go on to mate with multiple females. A key strategy for survival involves males seeking out and mating with immature females. These females have developed reproductive organs but have not yet molted to their full adult size and aggressive state.
When mating with an immature female, the male avoids performing the risky, self-sacrificial somersault and maintains a position far from her fangs. Since the immature female is not fully aggressive, the male is able to survive and can effectively plug her reproductive tract, securing his paternity before she reaches maturity. Even when cannibalism is avoided, the male black widow has a naturally short lifespan, usually dying soon after mating due to exhaustion or the inherent dangers of searching for mates.