Spi­ders the­o­ret­i­cally could eat ev­ery hu­man on Earth in one year

But the good news for us is they mostly eat in­sects – a whole lot of in­sects

The Denver Post - - NEWS - By Christo­pher Ingraham

Spi­ders are quite lit­er­ally all around us. A re­cent en­to­mo­log­i­cal sur­vey of North Carolina homes turned up spi­ders in 100 per­cent of them, in­clud­ing 68 per­cent of bath­rooms and more than three-quar­ters of bed­rooms. There’s a good chance at least one spi­der is star­ing at you right now, siz­ing you up from a dark­ened cor­ner of the room, eight eyes glis­ten­ing in the shad­ows.

Spi­ders mostly eat in­sects, al­though some of the larger species have been known to snack on lizards, birds and even small mam­mals. Given their abun­dance and the vo­ra­cious­ness of their ap­petites, two Euro­pean bi­ol­o­gists re­cently won­dered: If you were to tally up all the food eaten by the world’s en­tire spi­der pop­u­la­tion in a sin­gle year, how much would it be?

Martin Nyf­feler and Klaus Birkhofer pub­lished their es­ti­mate in the journal the Sci­ence of Na­ture this month, and the num­ber they ar­rived at is frankly shocking: The world’s spi­ders con­sume 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, who the au­thors note con­sume about 400 mil­lion tons of meat and fish each year.

Or, for a slightly more dis­turb­ing com­par­i­son: The to­tal biomass of all adult hu­mans on Earth is es­ti­mated to be 287 mil­lion tons. Even if you tack on an­other 70 mil­lion-ish 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, ex­ceed­ing the to­tal weight of hu­man­ity.

In other words, spi­ders could eat all of us and still be hun­gry.

To ar­rive at this num­ber Nyf­fler and Birkhofer did a lot of so­phis­ti­cated es­ti­ma­tion based on ex­ist­ing re­search into:

• How many spi­ders live in a square me­ter of land for all the main habi­tat types on Earth.

• 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 — be­cause Nyf­fler and Birkhofer don’t de­fine what “fa­vor­able” means in this con­text, one might as­sume it refers to dark, dusty places, like un­der the bed.

If you gath­ered up all the spi­ders on the planet and placed them on a very large scale, to­gether they’d weigh about 25 mil­lion tons, ac­cord­ing to Nyf­fler and Birkhofer. For com­par­i­son, the Ti­tanic weighed about 52,000 tons. The mass of ev­ery spi­der on Earth to­day, in other words, is equiv­a­lent to 478 Ti­tan­ics.

Spi­der bi­ol­o­gists have also gen­er­ally found that spi­ders con­sume ap­prox­i­mately 10 per­cent of their body weigh in food per day. That’s equiv­a­lent to a 200-pound man eating 20 pounds of meat each day.

Con­versely, it would take ap­prox­i­mately 2,000 pounds of spi­ders to con­sume a 200-pound man in one day.

In the end, spi­ders’ vo­rac­ity ac­tu­ally works out to mankind’s ben­e­fit. Since they pri­mar­ily feast on bugs, their hunger means fewer pests in the gar­den, fewer mos­qui­toes in the yard and fewer flies in the house.

The face of a bold jumper spi­der. Spi­ders eat at least as much meat as all 7 bil­lion hu­mans on the planet com­bined, who con­sume about 400 mil­lion tons of meat and fish each year. Joseph Berger, bug­wood.org

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