Thursday, June 1, 2017

Could Spiders Really Eat All Humans On Earth In One Year?

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Face of the Bold Jumper Spider - amongst the most 'dignified' of arachnids, though wifey disagrees.

Time to change the subject from Trumpism and move out of Trump World, at least for a time! Everyone needs a break from the endless political news cycle, after all. What better subject to move to than our  ubiquitous, eight -legged friend, the spider?

Four days ago as we were leaving for an appointment, Janice summarily stepped on a small spider trying to gain entrance to our abode, saying: "Sorry, Spidey, but not in our house!"   I asked her how she could commit such a dastardly deed on such an interesting little critter,  and added: "What if the first ever advanced aliens that visit Earth have the appearance of spiders?"

She replied without blinking: "Well, then I guess it will have to be interplanetary war."

The fact is that the Earth is as much the home of spiders - thousands of varieties - as it is for humans. One  recent entomological survey in North Carolina homes found - if that survey is any guide - the eight-legged critters are literally all around us. The tally came up with 100 percent of NC homes having spiders (often dozens), including 68 percent lurking in bathrooms (I often find them in the shower or scurrying near the toilet bowl), and more than three quarters in bedrooms.

My basic approach is not to kill them, unless it happens to be a Brown Recluse or Black Widow. I regard them as useful predators for insects such as flies, mosquitoes etc.  Janice's attitude is 180 degrees opposite, if she sees one she kills it. It's like a knee jerk reaction. This may have derived from a nasty spider bite she got while we were on a visit to Vermont (Rochester),  in 1998. The little beastie crawled up onto her and bit her on the neck leaving a smallish red welt that lasted for weeks. She never forgot or forgave the arachnid transgression. Her main regret was not catching it and becoming its judge, jury, executioner.

Anyway, according to spider biologists the planet's spider population has a collective weight of 29 million tons. That's roughly about the same as 478 Titanics.  They eat mostly insects, although some of the larger species have been known to snack on lizards, birds and even small mammals.  To fix ideas, I once observed a college roommate feed a small Anole lizard to a pet Tarantula. It was not a pretty sight. (It more or less stayed away from me, as I kept a pet gator.)

Here's another interesting fact: the world's spiders consume somewhere between 400 million and 800 million tons of prey in any given year. That means that spiders eat at least as much meat as all 7 billion humans on the planet combined,  If this is so, one may inquire if it is also possible that all those spiders gobbling all those tons of prey could gobble all the world's humans too - that is, assuming they had a yen and potential to do so.

To answer that question, two European biologists, Martin Nyffeler and Klaus Birkhofer published their estimates in the journal the Science of Nature.   To fix ideas, the total biomass of all adult humans on Earth was estimated to be 287 million tons. So, even if you tack on another 70 million tons tons to account for the weight of kids, it's still not equal to the total amount of food eaten by spiders in a given year. Thus the meat consumed by spiders exceeds the total biomass of humans.

In other words, spiders could eat all of us and still be hungry. When I read that from a recent article to Janice, she merely shrugged her shoulders and responded: "I knew you couldn't trust the little bastards! So when I see them I kill them!"

Aaarrrgh!   She was also skeptical of the figures both in the authors' original paper and in several subsequent articles including one appearing  in The Denver Post, and one in the Barbados Nation -when we were there the last week of April and first of May.

I pointed out that to arrive at the "magic"  number Nyffler and Birkhofer did a lot of sophisticated estimation based on existing research into A) how many spiders live in a square meter of land for all the main habitat types on Earth, and B) the average amount of food consumed by spiders of different sizes in a given year.

These numbers yielded some interesting factoids on their own. For instance, one study estimated that global average spider density stands at about 131 spiders per square meter. Some habitats, like deserts and tundra, are home to fewer spiders. On the other hand, spider densities of 1,000 or more individuals per square meter have been observed under certain “favorable” conditions — since Nyffler and Birkhofer don't define what “favorable” means in this context, I'm going to assume it refers to dark, dusty places like the area under my bed.

I also informed Janice that she ought to be glad that spiders' voracity actually works out to mankind's benefit. This is given that they primarily feast on bugs, their hunger means fewer pests in the garden, fewer mosquitoes in the yard and fewer flies in the house. Her reply? "Meh."

For now, I will have to act as the spiders' self-proclaimed protector in our home, and hope wifey doesn't catch too many of them scurrying about - seeking any corner for safe harbor. 

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