The Amorous Appetites of Adolescents and Arachnids: Sexual Cannibalism in the Australian Redback Spiders (Latrdectus Hasselti)

Conflicts between the sexes always bring me back to high school. This was a time of rude awakening in my life, when I first boyfriend taught me that boys and girls have conflicting motives when it comes to love. During one particularly ripe moment of teenage passion he whispers to me, "I could die like this". Now I suppose this was intended to be a sweet sentiment but since I'm not practicing necrophiliac and I'm prone to take things a bit too literally, I found this idea quite selfish and repulsive. Pushing him away for a moment, I imagined this awkward situation: What good is this dead guy to me? Where do I hide the body and just who is going to light my cigarette?

Some females, however, embrace this dark fantasy with wide-open chelicerae. For example, female Australian redback spiders (Latrdectus hasselti) routinely devour their complacent lovers during copulation. Not only are males completely nonresistant to female attack, but they also heedlessly tempt the female beast by performing a backward somersault during copulation. This maneuver places his plump opisthosoma in a vulnerable position, right in front of the mouth of his insatiable mistress. More often than not, she accepts his masochistic offer and proceeds to consume him during their carnal act.
The potential fitness benefit of sexual cannibalism is obvious for the female. Nutritional gain due to mate consumption can significantly increase her fecundity. However, the effect on male fitness is less readily apparent since male sacrifice results in the forfeiture of all future mating opportunities. Therefore, the persistence of sexual cannibalism in Australian redback spiders poses two evolutionary questions: Does sexual cannibalism represent a conflict of interest between the sexes or can male Australian redback spiders somehow benefit from sexual suicide?

In several other species of spiders, there is growing evidence that there is a conflict between the sexes. Males don't succumb so easily to females' lethal intentions and therefore may employ many different strategies to avoid being eaten. In fact, some clever (or cowardly) males may preferentially mate with females that are in a physically compromised state. For example, some species of male spiders prefer females that are in the compromised state of ecdysis (molting) and/or to approach females only when they safely preoccupied with other prey items.

Unlike most other sexual cannibals, the persistence of sexual cannibalism in Australian redback spiders may actually be a result of a male adaptive strategy rather than female imposed selection. First of all, male sacrifice in Australian red back spiders doesn't represent any loss of fitness for males since their intromittent organ breaks off during sex regardless of his mortal outcome. While most men I know regard this loss of "manhood" as a justifiable reason for suicide, the male redback has deeper motivations. Males that are cannibalized by females are permitted to engage in intercourse longer than males that are not eaten; and as a consequence, cannibalized males fertilize a greater percentage of the females' eggs. In addition, females that cannibalize their mates are temporarily satiated and less likely to copulate with other males. Oddly, female red backs don't experience an increase in fecundity as a result of this "love meal", apparently the male is too small to provide much nutrition and primarily serves as an effective distraction.

Perhaps, my immediate repulsion to my first love's sentiments was rooted in the fact that I'm a typical human female who exerts her own selfish selective pressures on males. However, unlike the Australian redback femme fatale, I select male behaviors that provide more long-term and domestic fitness benefits. Instead, why didn't my young love whisper, "I could …cook you dinner, take you shopping and do your dishes right now"? Still, I remain curious about the confused motivations of our human males. From where, does the seemingly maladaptive "sexual death fantasy" arise? I challenge you now, to explore the vestigial evolutionary significance of "hickeys"…if you dare.