A Moveable Feast

They say necessity is the mother of invention — I guess that’s why spiders found a clever way to order in, long before Kroger and Amazon began to lug customer’s grub. Not even a Costco cart is big enough to satisfy arachnid appetites but spiders rule when it comes to home food delivery. You see, it’s all about the web.

I don’t mean the Internet.

The menu of ingenious spiderweb designs includes: the classic spiral cobweb with its orderly silk scaffolding; messy 3D tangles rigged between available attachment points; carefully woven sheets scattered like picnic blankets across a lawn; funnels and trapdoors; and even a minimalistic single thread and sticky ball baited with pheromone-mimicking chemicals.  Gourmet or generic, webs deliver the vittles.And spiders are a hungry lot. They have to eat approximately 10% of their body weight in prey, each and every day.  Humans, by way of comparison, consume on average only 2–3% of our body weight—2.5 to 4 pounds of food per day. Now, I can already hear you bellyaching, “Not so fast, Kieran! Sure, 10% may sound like a lot at first but spiders don’t weigh very much. This hardly qualifies as extreme eating.” True, even the 12-inch Goliath Bird-Eating Tarantula is significantly smaller than most people. But, believe me, 10% can add up fast.

Based on published spider censuses (yes, I assure you there are people who do this for a living), there’s an average of 131 spiders for every square meter of land on Earth. Here’s a handy visual for metrically-challenged Americans:  Think of a square kitchen table that seats 4 people. Now imagine that table top covered with 131 peckish spiders. Next, see a vista of spider-covered kitchen tables, placed edge to edge like tiles across the entire landmass of our planet.

Remember, 131 is an average so in less hospitable regions the tables will have only a few patrons, while in other parts of the world each table may have up to 1,000 spiders patiently waiting for dinner to arrive. All told, there are approximately 27 million tons of spiders hanging out in the Earth’s forests, grasslands, plateaus, and deserts, our basements, attics, garages, and kitchen tables.

Before you shudder in horror, remember that insects are the spider-snack of choice and, consider for a moment, how buggy the world would be without these arachnid carnivores.

Scientists Martin Nyffeler (University of Basel, Switzerland) and Klaus Birkhofer (Lund University, Sweden) did just that.  They decided it would be fun to compute the global spider grocery bill and possibly add a peer-reviewed paper to their CVs in the process. They reviewed the work other researchers had done on the metabolic needs of spiders, assessed field reports on the number of prey captured and eaten by spiders, threw it all in a statistical blender, and published their calculations in The Science of Nature earlier this year. According to their recipe, spiders catch and eat 400–800 million tons of prey annually.

Let’s put that number in context, shall we?

  • Seabirds (all species) consume 70 million tons of food annually.
  • Whales (all species) consume 280–500 million tons of food annually.
  • Human beings consume approximately 400 million tons of meat and fish each year.

Still not impressed? Every year, the combined weight of insects consumed by spiders is greater than the total biomass of every person on Earth:

                      7.4 billion people x 130 lbs (avg. weight) = 400 million tons

There’s no doubt spiders play a significant role in managing insects, especially in forests and grasslands. The mere intimidating presence of spiders has been shown to limit the feeding behavior of some insects, reducing plant damage.

Spider prey includes insects that are of interest to humans due to their role as pests or disease vectors, but they’re not particularly helpful in managing agricultural pests.  Nyffeler and Birkhofer hypothesize that cultivated lands have less insect diversity and fewer insects overall than undisturbed lands, making them almost as unappealing to spiders as grocery stores.

Grocers must adapt to modern shoppers, though, and spiderweb technology could help capture the home delivery market!


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© 2018 Next-Door Nature. Originally published in Pest Control Technology Magazine (February 2018). Reprints welcomed with written permission from the author. Thanks to the following photographers for making their work available through the Creative Commons license: Tibor Nagy, Christopher, varmfront.se, Katja Schulz, and Marcus.

Long-stemmed

Daddy longlegs are the jazz cats of the arachnid world!

This realization came to me as I watched a single backlit note poised on a broken music staff bebop across the asphalt path in front of me. A soundtrack of jazz piano greats immediately began to play in my head — Willie “The Lion” Smith, Thomas “Fats” Waller, Art Tatum, Thelonious Monk, and Dave Brubeck, to name but a few. Chill dudes whose spider-like fingers strode, slid, bounced, and stomped across the keys.

Jazz has evolved and diverged from it’s start in the late 19th century as  ragtime and Dixieland into a genre so diverse it can be difficult to define, or even to list all the variations: Swing, Cool, West Coast, Modal, Free, Fusion, Funk, Cu-Bop, Post-Bop, etc.

The harvestmen, as daddy longlegs are also known (that even sounds like a 1950s jazz band, doesn’t it?) have an even longer and more impressive history. They’re a vast, improvisational set that spans millions of years and many taxonomic octaves, with over 6,500 named species worldwide (experts estimate there may actually be more than 10,000). And while not all the players in this big band have long legs, the ones who hangout in my neighborhood— eastern harvestmen (Leiobunum vittatum)— are definitely long-stemmed.

These invertebrate daddy-o’s are arachnids but they are NOT spiders; they’re more closely related to mites and scorpions.  Harvestmen don’t have a spider’s tiny waist… or venom… or silk (so no webs)… and they have only two eyes instead of eight.

Jazz musicians need to maintain their instruments to get the best sound; piano hammers need to be voiced, strings tuned, reeds moistened and valves lubricated.  Daddy longlegs are similarly serious about the tools of their trade, cleaning each leg after a meal by threading them through the pincers by their mouths.

Harvestmen are a gregarious lot who periodically congregate in the hundreds or even thousands. Scientists have suggested these spontaneous jam sessions might occur in response to climatic conditions or provide some protection against predators… but it’s pretty clear they aren’t making music (that can be detected by the human ear, anyway).

Members of Order Opiliones are exceptional even among arachnids. They can swallow small pieces of solid food, whereas their cousins are limited to a liquid diet. Conversely, daddy longlegs sip oxygen through their legs into a trachea, while other arachnids respirate through a gas exchange organ called a book lung. That’s probably just a warm-up, though. Like jazz, daddy longlegs are both familiar and mysterious. Little research has been done on these species… and who can say why? Maybe they’re a bit too avant garde to have a large fan base among researchers.

Or it could be the hours they keep and the dives they frequent. See, eastern harvestmen have more in common with jazz pianists than an impressive hand (or leg) span. Say what you will about the pleasures of sitting outside at a warm summer evening festival, lounging on a blanket in the grass while listening to a live performance — you’ll hear no argument from me. But to my mind, jazz is an urban art form, and the smokin’ hot licks happen in basement clubs. An intimate corner, low lights, insulated from street noise, maybe just a little damp…

Now that the kind of gig daddy longlegs’ dig.

 

[Thanks to the following photographers for making their work available through the Creative Commons license: Rob Swatski, Leslie Bliss, Rob SwatskiLuis Fernández Garcia, and schizoform.  © 2017 Next-Door Nature. Reprints welcomed with written permission from the author.]