Occasional (Halloween) paper: A mother gives her all

Because effective is not the same as efficient.  Yes, those big webs can capture more prey.  But they don’t seem to capture more prey per spider.  It’s like, 100 spiders cooperate to build a web, and that web captures 80 times more prey than a single spider could alone.  That’s a net loss!  The average spider is eating 20% less.  The numbers don’t work out.  (And remember, kids, economics are everywhere.)

Okay, but then this just flips the question: if being social is inefficient, why are any spiders social?

The answer seems to be that under certain specific circumstances, being social can still be a net positive.  First, if the spiders are living in a prey-rich environment, with lots and lots of insects buzzing around, this can make the per-spider nutrition hit less painful.  Second, if it’s also a predator-rich environment, the large webs provide significant protection from predators.  And third, if it’s an environment with extremes of weather — one that swings from humid to very dry, or where there are often gusts of strong wind, or sudden heavy rainfalls — the big webs can provide protection and stability.  Spider silk is an excellent insulator, so the inside of a social web will keep a constant temperature, and the spiders don’t have to worry about being washed out or blown away.

So, if environmental conditions are just right, being social becomes a plausible, marginally successful strategy.  It’s still not hugely successful — again, there are only about 20 social species out of ~40,000 — but there is a niche.  The social spiders are taking a hit in nutrition in return for enhanced security.

Of course, this means that while social spiders are more safe, they’re also more hungry.  They’re always hungry.