You could balance a spider's brain on a needletip.
Each species of spider is able to spin a certain type
of web — be it funnel, sheet, or orb. The force of an insect hitting the
center of an orb web is comparable to that of an airplane hitting a tennis net1.
That the web doesn't explode in a sparkling shower of fibroin
is thanks to the aerodynamics of the individual strings.
The web silk does not become fibroin
until it leaves the spider's body. Before then, it's a protein
with a molecular mass of roughly 30,000 Dalton.
Upon being ejected by the spinners, it polymerizes into the substance we know
as fibroin, a new protein whose molecular mass has increased tenfold. To this
day, polymerization of web silk is a mystery.
Bacteria and fungi love protein. Decomposition is the work of mycelia and flagellates.
Spider web is a protein, but it doesn't decay. There are cobwebs thousands of
years old — fibroin ages well.
Spider silk is full of pyrolidin,
and potassium nitrate. Pyrolidins bind water
(the adjective is "hygroscopic"),
preventing the web from drying out — you can also find them in plant poisons
and natural dyes. It's more concentrated in the sticky catching threads. The potassium hydrogen phosphate makes the web acidic and resistant to fungal and
bacterial growth. The low pH of acids causes the denaturation
of proteins, a phenomenon you've observed firsthand if you've ever opened a carton of sour milk. This is where the potassium nitrate comes in: it acts like
Steel is one of the strongest metals we have: it stretches by 8% before breaking. Nylon is a bit more elastic--it'll go about 20%. The web of an
orb-weaver is good for 30-40%. The thread of the Stegodyphus sarasinorum
is constructed in a weave and will stretch to twenty times its original length.
Different spiders have different
glands for the production of web proteins. Across the vast tapestry that is spider,
there are seven common glands. Some spiders have more than others; none
have all seven.
A typical spider has three pairs
of spinners; a typical spinner contains thousands of tubes, all connected to the
protein-secreting glands. The appropriate measurements are tenths and hundreds of micrometers. The thinnest strand of spider silk ever measured came in at roughly
.02µm. We see spider web only because it shines in the light.
The glands are a varied and complex
Tubiliformes make thread for cocoons;
Aciniformes make thread for bundling up prey;
Ampulleceae (major and minor) make non-adhesive walking thread;
Aggregata make sticky material for the threads;
Pyriformes make outer anchoring threads;
Coronatae make the core of the adhesive threads, which are coated in the
secretions of the aggregata.
The bodily strain of building a home from secretions is large. Orb-weavers eat their own webs to
conserve resources, ingesting the night's ragged ends to be recycled for the
next morning's refinishing.
The subtleties of spiderweb
construction are comparable to those of human homes.
Virtually all spiderwebs fall into
one of three categories: orb,
Big, prototypical yarn webs you buy
at the party
store are imitations of orb webs: the
concentric mesh sheet with the spiral.
Sheet webs are a rarer
phenomenon. Three-foot ladder webs in the rainforest bounce prey off and deposit them
in silk reservoirs for later consumption.
The spatial web is the work of a
disorganized spider: a tangle of thread anchored to corners. Black widows like these.
Of course, there are exceptions. The
trapdoor spider fits the top of an earth hollow with a flat rock and
attaches a trip wire.
The construction of suspended webs
is a cavalier process. In orb and sheet webs, the spider
finds two upright structures from which to hang the top thread. Instead of
depositing a strand at one structure and walking to the other, she throws the web. This done, she reinforces
the line with thicker thread and descends from its center, creating a Y shape
from which the remainder of the web radiates. Non-adhesive and adhesive strands
are deposited accordingly: usually the mesh structure is non-adhesive walking
rope while the spiral holds prey in place.
I loved playing with spider's web as a kid--the invisible pull between fingers, the tiny sounds of threads popping under tension.
But more practically:
Fishermen casing the waters off the
coast of French Polynesia use the gold-colored thread of the Nephila as a fishing
During the Second World War, Americans used the thread of the black widow
as hairs in telescopic gun sights.
At the beginning of the eighteenth
century, Frenchman Bon de Saint-Hilaire made gloves from fabric refined from spider's web. In this
process he found that one cannot possibly refine spider-silk profitably: he
calculated that he'd need over a million egg cases to produce a single kilogram
1 From ABC — fourth source.
Ed Nieuwenhuys, "The Spider Web
Knowledge Adventure, Inc.