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Coin Spiders Cut Off Their Genitals After Sex To Better Protect Their Females

Spiders have it hard when it comes to reproduction. Many species of spiders go for the ultimate sacrifice once copulation is over. After the act, females feed over the males, almost as if it were part of some sort of ritual. Well, as gross as this may sound, the coin spider (Herennia multipuncta) has it even worse: the male feeds on its own genital parts. A new study has attempted to put into perspective the gruesome self-mutilation.

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To begin with, the male is four times smaller than the female. Trying to get laid itself is problematic. The male coin spider has to first lure a female. If he succeeds at this difficult task, he then has to protect his pregnant female from other males. The males were observed to guard the females aggressively. What is grotesquely bizarre is one of the ways of doing so: the coin male spider bites off one or both of its reproductive organs known as palps. This is not fatal to the spider which will then live the rest of its life as an eunuch (partial eunuch or full).

We’ve heard of post-sex body mutilation for spiders, but this one goes beyond all the others.

A new research published in Behavioural Ecology and Sociobiology indicates that this could be difference-marker for the spiders to ensure that their genes, and only their genes, move to the next generation.

Coin spiders have enough sperm for only one sexual encounter. So, getting rid of their palps where the sperm is stored is not much of a problem. Actually, it might even be of an advantage to them. The palps make up 10 % of the body weight, and therefore, shedding them off makes them leaner and fitter. More importantly, they are able to deal with the competition as they are now more ‘endowed’ physically.

Now, why is there the need for coin spiders to protect their females after they have succeeded in luring and impregnating the latter? As difficult as it was trying to find a mate, it is perhaps even more so to prevent other males from fertilising the same batch of eggs. Therefore, as a way of keeping other males from inserting their genes into the eggs, the eunuch coin spiders fight to protect their offspring from being tainted by others.

The reason as to why would the spiders cut off their very own genitals after they have been put to use remained a mystery in the world of science. This study might have resolved the long-lasting mystery. The researchers observed virgin males and eunuch ones (those having already used up their stored sperm) and found that the latter were more aggressive in attacking the competitors, and had more endurance, probably as a result of the reduced body weight. Furthermore, they were also able to keep closer to their females.

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