Humans are not the only fathers capable of giving it all for the sake of their progeny. The animal kingdom is teeming with fathers that are downright heroes. For instance, male redbacks and dark fishing spiders would voluntarily throw themselves into the clutches of their mated female and eaten… never again to procreate or see the light of the ensuing days. This seems disturbing. How could mating be evolutionary costly for these unfortunate yet amazing spidey dads?
Sexual cannibalism of spider fathers
The mating of spiders in which the female eventually devours the male is one the most fascinating animal couplings. In this case, male spiders that engage in the rituals of courtship and copulation are likely dead fathers. Literally hungry for more, the females consume their mates in an act called sexual cannibalism. The devouring of another individual of the same species could occur before, during, or after copulation. The female spiders are usually the sexual cannibal, perhaps, because they are often larger than their male counterparts, and so, more physically dominating. Cannibal female spiders are often hostile and unenthused to mate. Thus, male spiders ought to be valiant to approach and fancy them with their moves. An impending death may be too much of a price to pay but these hopeless romantics are willing just so they can be fathers to their mate’s soon-to-be spiderlings.
Spider Fathers avoiding sexual cannibalism
Sexual cannibalism in spiders is real. However, not all spider dads end up harmed after mating. Many male spiders, in fact, do not end up in the females’ gut. Not all female black widow spiders consume the fathers of their prospective spiderlings. Thus, the notion that all black widow females are sexual cannibals (hence, the “widow” on their name) is a misconception.1 There are also male spiders that came up with their own tricks. One fantabulous example is to play dead. By appearing stiff dead, male wolf spiders avoid ending up as a palatable snack after copulation.2 The apparent death trick is called thanatosis.
Altruistic Spider Fathers
While certain spiders dodge sexual cannibalism, there are those that do not just welcome it but also incite it. These male spiders are the quintessential altruistic spider fathers. Male redbacks (Latrodectus hasseltii), for instance, encourage adult females to engage in sexual cannibalism. After inseminating the adult female, the male somersaults to bring his body close to her mouthparts like a cue saying “eat me now”. The female spider spits gut juice, and then feeds on him. If lucky enough to live after that, he returns to her, filling her with more sperm, plus a nutritious “meal”. Eventually, he dies by succumbing to his injuries from slow cannibalism. Another example is the male dark fishing spider (Dolomedes tenebrosus). As if a befitting sacrifice to his female, the spider curls up with no hesitation. Thus, one may wonder: “Why would these male spiders sacrifice their life for a one-time sex?” It seems unsound and evolutionary counter-productive. Research3 on dark fishing spiders implicated that cannibalism improved offspring survival. Females that ate their spiderlings’ fathers had more surviving offspring than those that did not. The spider dads seem to possess unknown components that significantly boosted their offspring size, fitness, and survival.
Redback spider. (Credit: Ryan Wick, Flickr)
Dark fishing spider. (Credit: Charles de Mille-Isles, Flickr)
In essence, the self-sacrificing behavior of these spider fathers is a manifestation of how ready they are to die for the sake of their progeny. With the assurance that their genes are passed on to their offspring, they served a remarkable purpose as befitting fathers to their spiderlings even if it means acceding to sexual cannibalism.
— written by Maria Victoria Gonzaga
1 Crawford, R. (2015). Myth: Black widows eat their mates. Retrieved from http://www.burkemuseum.org/blog/myth-black-widows-eat-their-mates
2 Seriously Science. (2016). Male spiders play dead to avoid “sexual cannibalism.” Retrieved from http://blogs.discovermagazine.com/seriouslyscience/2016/05/26/5406/
3 Choi, C. (2016). Journal Club: Self-sacrificing male spiders assist in their own cannibalism to aid offspring. Retrieved from http://blog.pnas.org/2016/10/journal-club-self-sacrificing-male-spiders-assist-in-their-own-cannibalism-to-aid-offspring/