Xenophilic spiders:
I was blessed with having some very bright friends coming up through the public school system.  A couple of them fixated for a time on the word “Xenophilous.”  They would apply it to almost anything.  They said it meant “frost proof.”  I believe that should be “cryophilous.”  The use of the word always recalls those happy days.

Spiders are generally solitary predators.  The female will eat her consort after mating, at least in some species.  But certain species will form communities.  (Come into My Parlor ECONOMIST vol. 406 no. 8820 January 26, 2013 page 72) At least one advantage of this is that the females can band together to protect the young from males.  That makes sense.  An unattended minor is cheap food in the wild.  If there is no female to protect a young spider it is doomed anyway so it makes perfectly good sense for a male to chow down on it. 

What was a surprise was that some of these communities consisted of more than one species.  That has the pro’s baffled.  Here is one species defending the offspring of another species.  The going explanation for altruism is that of Robert Trivers: one is altruistic toward ones kin because they carry a higher proportion of ones genes than a total stranger carries.  But here that calculation fails: different species means fewer shared genes and no opportunity for genetic exchange.

Often species will cooperate with species which are quite different.  The crocodile bird will clean the teeth of a crocodile for the sake of little tidbits it finds.  The nutritional cost to the croc is trivial, but getting its teeth cleaned means healthier gums and longer life.  Such arrangements are generally between very different species occupying different niches.  These spiders are so alike in their food choice and appearance (and obviously choice of location) that it was not initially clear that they were not all the same species. 

It should be clear to us that there is one potential advantage to having different species all doing the same tasks.  A gene pool can only be so big.  So putting two species into the same community means that twice the number of total spiders can live together.  Whatever the advantage of the communal style it is probably better with bigger numbers, at least over a range, else it would never have appeared.

I think I shall not trouble the researcher with a suggestion on this.  I can already hear the words, “Another nut.”

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