The Miracle of Spiderwebs – Discovery Institute

Photo credit: edbuscher, via Pixabay.

Editors note: The following is an excerpt from the newly released book,Animal Algorithms: Evolution and the Mysterious Origin of Ingenious Instincts, from Discovery Institute Press. Dont miss theupcoming webinar with Eric Cassell and Casey Luskin, Thursday, December 9, from 4 to 5:30 Pacific time.Register here.

Whats miraculous about a spiders web? said Mrs. Arable. I dont see why you say a web is a miracle its just a web.

Ever try to spin one? asked Dr. Dorian.

Spiders are another of natures master engineers. About half of known spider species (order Araneae) construct webs made of silk. Spiders can make different types of silk, depending upon its function. For example, the golden orb-weaver spider has seven kinds of silk glands, with six spinnerets.1Some is used for spinning webs, of course, but other types are used for wrapping prey and encasing eggs. Silk can be stronger than steel of the same thickness, can stretch more than rubber, and is stickier than most tape.2The Goulds describe silk as easily the most remarkable building material on the planet, and it has one source: arthropods.3Despite great effort, humans have yet to produce anything functionally equivalent to silk. Through genetic engineering, attempts have been made to duplicate it without success. The main challenge is replicating the sophisticated and information-rich protein molecules found in the silk produced by spiders and other silk-producing arthropods such as silkworms proteins that are nearly double the size of average human proteins.4Smaller proteins do not have the strength or flexibility of spider silk. Given the advanced genetic and manufacturing technologies available today, it is remarkable that spider silk still cannot be duplicated. This illustrates just how advanced the engineering design of spider silk is.

Orb webs are the most common and familiar types of spiderwebs. A typical garden spiderweb is made of 65 to 195 feet of silk.5The webs consist of sticky catching threads; radial spokes for holding the sticky threads; bridge threads that act as guy-lines for holding the web up; signal threads that inform the spider through vibrations sensed in the legs that prey is in the web; and drag lines for access into the web from her home.6The silks employed in the different uses are each unique, being constructed of different combinations of proteins. The types include slinky for stretchiness, zipper for flexibility, and lego for toughness.7Construction of the web is a purposeful, goal-driven activity. This becomes particularly obvious as one observes the process in videos available on the Internet.8

Various spiderwebs, even among spiders of the same species, are far from identical. The most obvious reason for the differences is that each is tailored to its specific location. As the Goulds explain, Every set of initial anchor points is different; the number of radii is contingent on opportunity; the beginning of the sticky spiral depends on where the longest several radii turn out to be. In short, each web is a custom production.9The Goulds postulate that spiders have a form of mapping ability that enables them to implement general design principles in a wide variety of circumstances. This is demonstrated, for instance, by spiders successfully making repairs to damaged webs.

Another source of difference is function. When we think of spiderwebs, we tend to imagine the kind most commonly encountered the netlike webs spread between trees or attic rafters or walls. But there are various other types, including ones that function as trapdoors into spider burrows, collars that extend out from burrows, and webs that function as tubes on tree bark that can also have hinged doors.10

I mentioned signal threads above. They tell a spider that prey is present on the web, but they convey a lot more than just that. Spiders are able to determine both the angle and distance of the prey from the center of the web. They are able to determine the prey location using the same basic technique we use to determine the location of the source of sound. Humans use the difference in intensity of sound received by our ears to estimate the relative location. Spiders do something similar based on the intensity of vibrations received, in their case sensed through eight legs.11Obviously the algorithm used in processing information from eight sensors is much more complicated than just the two sensors that humans have. And thats only the half of it. Experiments have demonstrated that spiders can store the coordinates for the locations of at least three different prey trapped in the web.12

Providing credible evolutionary explanations for the origin of silk and web design has proven problematic. Several theories have been proposed for the origin of both, but none have been generally accepted.13Biologist and spider specialist William Shear concedes that a functional explanation for the origins of silk and the spinning habit may be impossible to achieve.14One complicating factor is that the webs of some spiders that are more distantly related are nearly identical. Shear writes, It appears probable that several web types are the product of convergent evolution that is, that the same web has evolved in unrelated species that have adapted to similar environmental circumstances.15But as I will argue in Chapter 6, that is an unconvincing explanation for the origin of complex programmed behaviors.

A more fundamental challenge for those seeking to provide a detailed, causally credible explanation for the origin of silk and spiderweb architecture is the number of genes involved in producing silk, and the complex genomes of spiders.16After decades of failed attempts to provide a causally adequate explanation, one can be forgiven for concluding that we have no compelling reason to assume that a step-by-step evolutionary pathway to such an information-rich substrate actually exists. And as we will discuss later, there are now some positive reasons to consider that such information-rich systems have for their source something other than a purely blind material process. Here, suffice it to say that the behaviors and functions associated with both silk and web spinning exhibit many characteristics of human engineering, and engineering of a very high order.

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The Miracle of Spiderwebs - Discovery Institute