Happy New Year! Also, the world will soon be shrouded in darkness and man’s reign shall end.

Posted: January 1, 2014 in Arthropods

Well, it has been a long time since this blog was up-dated. I have a variety of intricate excuses for this; ranging from escaping rogue Russian spies whilst continuing a passionate affair with a dispossessed Polish noblewoman; to helping helping African orphans escape the militia of a murderous dictator whilst seducing the manager of the orphanage, to parachuting into Pakistan to halt the Taliban’s attempt to build a nuclear missile and rescue a captured, sexy-yet-deadly CIA agent. After all, if you’re going to lie, you might as well lie big. The Polish noblewoman, though, is totally real. And hot.

The plain truth, though, is that I simply forgot that I actually had this blog. So…y’know, sorry about that.

You should see the excuses I make for forgetting Christmas presents.

Now, there are many sayings in life which can instantly fill you with dread, ranging from ‘Hello, this is your bank manager, and there seems to be some trouble with your account’, to ‘Say another word, American dog, and you die”. But surely, the most terrifying thing you will hear today is not how much debt you’re now in, how close the world has come to nuclear war in the last sixty years, how fragile the threads that hold together our mockery of a civilization are, or how much your next power bill will be.

No, it is simply this.

“Some. Spiders. Live. In. Groups.”

It is possible that your brain, in a futile attempt to stop you from realising the true horror of the universe, blocked the above sentence from your consciousness. So go back, and read it again.

Finished crying yet? Good.

The spiders loath the taste of tears, and you don’t want to make them…hungry. Image credit: http://www.historycarper.com/wordpress/2010/kingdom-of-the-spiders-aka-nails-creek/. Nest is attributed to Guatemalan long-jawed spiders, aka Tetragnatha guatemalensis.

Yes, not all spiders are solitary. Although they are generally regarded as extreme individualists, to the extent that spider sex frequently results in the female eating the male (who sometimes willingly feeds himself to her, because males are stupid in the presence of females in all species) some spiders are known to form colonies, because God hates you. The only slim crumb of comfort is that, of the around 40,000 known spider species (which my arachnophobic friends insist is 40,000 too many) just over twenty can really be classed as social. Incredibly, however, this behaviour appears to evolve quite a bit; with these social spiders scattered across eight different families; meaning that spiders becoming social has happened more than once (Agnarsson et al 2006, well worth reading for the simple sentence “spider sociality is significantly spindly”). As to why it evolves, the most common explanation (besides the obvious ‘vengeful deity’ theory) is that it arises from maternal care patterns. In some species, for a number of reasons (geography, etc) there may very strong selection pressures against young spiders dispersing, as they do in most species. Thus, ‘social’ spiders will be selected for; and over time the species will become more communal. Advantages, of group living include saving on ‘per spider’ silk usage, access to larger prey, predator defence, and easy access to mates.

Only horror lurks under that web. (Image credit; http://bio-lenguasext.blogspot.co.uk/2012_07_01_archive.html, Webcredit; Anelosimus eximus)

One example of a communal spider is   Anelosimus eximus; which is found throughout South America. The spiders co-operate in web construction, maintenance, and cleaning, and also, horribly, in prey capture. They even have a form of co-operative child rearing, where female spiders regurgitate their meals to provide food for youngsters. Most awful of all, however, is the fact that each colony can contain thousands of individuals (Smith 1986). How that was worked out, we don’t know, and neither do we wish to, although we guess it involved a lot of traumatized PhD students. It has also been suggested that this spider is eusocial, like most ants, wasps and termites, because it is thought most females don’t actually reproduce. This system probably arose because a large proportion of the spider’s food requires communal capture; thus spiders which can compete better have more resources to devote to reproduction. In hard times, when few insects/other arthropods/hobbits/children wander into the web of horror, the fact that some females monopolise all the food captured, despite the fact it was caught cooperatively, possibly  allows the colony to survive.  (Rypstra 1993). Also, living in groups allows better protection against kleptoparasitic spiders, which are other species of spider which try and steal the food caught in webs. Larger groups of spiders are better at protecting their food than smaller groups (Cangialosi 1990).

“You know what? We’ll get a take out” (Image credit: http://thinkjungle.com/rainforest-life/rainforest-spiders/)

However, ironically in  the spider Agelina consociata, it appears that actually spiders living in large groups have a lower food intake than those spiders in smaller groups, leading to lower egg production. Like A. eximus, co-operative hunting is common, and a swarm of as many as 40 spiders can feed on what is euphemistically called a ‘prey item’. But most of what is caught can readily be handled by a single spider. A possible explanation for this is that these spiders are rabid Communists, continuing to live in a commune even though it self-evidently doesn’t work. A more reasonable explanation, though, is that these spiders live in the West African rain forest, which, as the name suggests, can be rather rainy. This rain destroys spider webs fairly easily. By banding together to build and repair webs, individual spiders end up spending much less energy on web-building than they would individually, which presumably more than outweighs the fact that other spiders keep nicking all their food.

The war against the Spider-King will be won with blood, sweat, tears and a fire hose. (Image credit: http://apropok.blogspot.co.uk/2008/09/szocilis-pkok.html)

Some spiders are vegetarian – or at least, mostly vegetarian, like that one friend we all have who “never eats meat. But I do like fish, and sometimes if some is going I’ll have that chicken”. Bagheera kiplingi feeds mostly on plant leaf tips and nectar. These spiders have been observed to share nests, and guard eggs and hatchlings, suggesting that this species is social to some extent (Meehan et al 2008). However, its also worth noting that cannibalism has been observed among  these spiders, which is pretty anti-social, to say the least.

Its probably useful to note that, so far as I’m aware, none of these spiders pose a threat to humans. Although if you come home one night and find that a bunch of communal spiders have taken over your home, it might be best just to let them have it.

 

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