Tangled Webs

“Oh what tangled webs we weave, when first we practice to deceive” – (Sir Walter Scott, 1808, Marmion)

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A brown widow (Latrodectus geometricus) captures a wandering spider (Phoneutria sp.) in a disorganized tangle web outside of Puerto Maldonado.

A simple silken strand, braided and woven into a web, has captured the imagination of poets, naturalists, and researchers alike. The arachnid has been both deified, and demonized throughout the ages, and the archetypal imagery, an inspirational thread connecting past and future; from the fishing net, to the neural net.

Though most will be familiar with the highly publicized “Howitsmade”, Biomaterials-type narrative, listing the amazing properties attributed to spider silk: tensile strength, resilience, elasticity, etc… less discussed are those remote, cob-webbed corners of the phylogenetic tree, those extreme and bizarre adaptations which offer a varying perspective on a familiar sight.

Scoloderus, Theridiosoma, Cyclosa, Deinopidae, Argiope…

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… the names are a quixotic amalgamation of mythology and modern science.

But before we begin weaving these disparate threads into a story, there’s an underlying question, and it’s a question which can be applied to everything we learn, “Why? Why spend one’s precious time reading something when we are inundated with information? Why learn about spider webs, when there’s a world wide web to explore?” It’s not an easy question to answer, and certainly not one which will satisfy everyone; however, maybe in understanding the prototypical web, we can better understand how the world is connected, in a thread which spirals outwards from our very consciousness (extended cognition theory), to the outer confines of our physical universe (String theory).

But at the centre of the web, the hub, lies a spider…and that’s where our story begins, some 187 million years ago when the first web building spiders appeared in the fossil record. The arachnid’s story can be traced back further still to the more ancestral Mygalomorphs (to which the maligned Australian Sydney funnel web and the Tarantulas belong). Though they did (and do) possess spinnerets (silk producing organs), their use is principally confined to swathing a protective cocoon for their eggs, and as a means of relaying external vibrations into their burrow. They relied chiefly on their agility, speed and strength to surprise and overpower prey, rather than the capture webs used by the more derived orb weavers (Araneomorphs).

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Tarantula (Pamphobeteus crassifemur) exhibiting parental care of juveniles at the Tambopata Research Centre.

Like most evolutionary success stories, what we know as the orb web didn’t originally appear as the fully-fledged, architectural success story we currently know, glistening with dew and our admiration in the morning (and later, as we blunder into them, resentfully scraped from our faces). Rather, it’s thought to have evolved from the ground up; low-lying webs laid in a sheet, which gradually incorporated vertical tangle threads, and finally moving off the ground entirely, a response to the evolution of flight in insects.

 

All Credit for this amazing diagram goes to: F. Vollrath and P. Selden AR Ecology, Evolution, and Systematics 2007 (modified from Vollrath 1998.

The stultifying diversity of the spider web can be fundamentally simplified into two distinct flavours; those formed by cribellate and ecribellate silk. The former relies on a specialized organ, the cribellum; a plate with thousands of micropores through which silk is extruded, and then combed into a wooly (hackled) texture via specialized hairs (the calamistrum) on the spider’s legs. This silk isn’t “sticky” in the conventional sense, but rather entangles prey by virtue of its micro-architecture, which is so fine that it is subject to Van Der Waal’s forces (a weak electrostatic force resulting from the combined instantaneous dipole moments (induced polarity)), which bind weakly, but over a large surface area, to the insect’s exoskeletal cuticle. Simply put, there is both physical entanglement and electrostatic attraction at a small, but significant scale.

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Cribellate silk with its characteristic wooly appearance held by an ogre-faced spider (Deinopidae).

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One can see the trapezoidal web as it’s held between the elongated forelegs of this ogre-faced spider (Deinopidae). It is stretched up to 4 times its original size as the web encompasses the prey.

Part II will explore the divergence that created the ecribellate araneomorphs, and the incredible radiation in web design. Put in a way so as to bait the click; “The weave in the web: Catching wonder – the lure, the snare, and the sling”.

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