Coin Spiders Self-Emasculate after Mating: Survival of the Genes


Much has been discussed about the cruel phenomenon of sexual cannibalism practiced by the famous black widow spider but not many know about another crazy phenomenon practiced by a male coin spider. These male spiders (Herennia multipuncta) are one of the greatest lovers in the nature. These tiny spiders have the courage to propose a female almost four times its size, which, if hungry rejects the proposal and preferably feeds on the male. However, scientists observed that if the male is lucky enough to woo the female, the male after mating are seen to bite off their genitals. The purpose of this strange self-emasculation was not known so far. 

In a recent study, scientists claim that they now know why the male spider takes up such an extreme step of castration, as this gives coin spider a benefit over their intact rivals. These coin spiders in their lifetime can produce sperms enough for just one sexual intercourse. So after a successful mating has been done, it is wise to ditch the extra weight of palps (sperm transferring organs). This way the arachnid becomes lighter and has a better chance to defend his impregnated partner from competing rivals.

Eunuch behavior

Protecting impregnated partner is especially very imperative as numerous males can fertilize same lot of eggs. Therefore, this helps the male coin spider to ensure that his genes get passed down to the next generation of offspring. As an extra assurance, males chew off to abandon his genitals, plugged inside his partner, in short blocking up the female reproductive parts for the competing males. This behavior has been termed as eunuch behavior. Such male becomes an agile fighter and protect their partner. Researchers believe that as coin spiders have only one chance to ensure their gene carrying offspring are born and therefore, they are ready to do whatever it takes to ward off its rivals.

Although male coin spiders are extremely loyal to their partners, but the same cannot be expected from the female who may not think twice before feeding on his partner when hungry. After all, one-sided love is always painful isn’t it?

Source: IFL Science

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