Spiders' Webs

CORE Metadata, citation and similar papers at core.ac.uk Provided by Elsevier - Publisher Connector Magazine R364 Quick guide accordingly, the decision rules guiding the animal’s locomotory and manipulative movements can best be described (and analysed) Spiders’ webs as orientation behaviour. Indeed, the web-building Fritz Vollrath behaviour of orb-web-building spiders provides an excellent example of an organism solving a What is a spider’s web? Webs complex task of spatial provide spiders with a means to orientation by the iterated trap their food and, in some application of simple local cases, a place to shelter. Webs behaviour patterns. Thus, one can consist of blends of different silks, model the garden cross spider cleverly combined for Araneus diadematus as a virtual functionality. Take the ‘typical’ orb ‘spider robot’ in order to explore web of the common garden spider and modify the spatial world of (compare the photo on this page), digitized spider webs. Such an which has evolved to take out-of- approach shows that a small plane loads at optimized number of very simple behaviour The orb web of Argiope argentata shows deflections. To be able to do so, patterns are sufficient to generate well the flexibility of web design. Here this web needs to incorporate into accurately the characteristics of a only one ‘arm’ of the typical St Andrews one structure the mechanical real spider’s web. Cross was executed. The function of properties of very different types such a stabilimentum, as it is called, is still unclear: is it there to confuse of silk: the fairly stiff, radius silk How are webs thought to have predators, to attract bees or to firm up threads and the extremely soft, evolved? Spider web structures the web? extensible and sticky capture silk and silks began their co-evolution threads, which are fixed on the about 400 million years ago, at first breaking. This intriguing micro- radii by stringy silk cement. probably as a protein cover to mechanism relies on water Spiders are important and highly protect the animal’s eggs and plasticizing the core fibres of the successful predators. Most of the young. Webs then evolved web, as well as providing surface hundred or so spider families have different functions, including tension to power the windlasses web-building members. Their webs acting as a kind of wall-paper for that roll up into tight balls the range from two-dimensional sheets the animal’s burrow and modifying structural core fibres stretched by to three-dimensional tangles, with the hole into a simple trap by the impact of an insect. These members of ten families building radiating lines that inform the spiders have evolved to produce the familiar orb web. The spider’s lurking spider about things web fibres that have an aqueous web is primarily a trap, mostly for beetling around outside. Even coating, supplied and maintained insects; it retains the contacting such simple lines expand the by hygroscopic compounds to insect and informs the waiting animal’s anatomical phenotype attract the required water spider about the location and many fold by incorporating the molecules from the atmosphere. status of the prey. Whether it is a body into an extensive silken net. Other orb-web spiders, such as static filter or a dynamic net The aerial webs of the ‘modern’ Uloborus spp. in the hackled-band swaying in the wind, the web spiders began to evolve perhaps cribellate family, negotiate the always relays vibratory signals of 200 million years ago and are prey’s kinetic energy in a totally considerable complexity. The great superb examples of ‘extended different way. At considerable cost ecological diversity of the potential anatomy’. These webs also nicely in both time and energy, this prey is reflected in the great illustrate the close interaction of spider combs out its capture silk diversity of web designs. Of these, material and behaviour which to form a loosely twisted, dry rope the orbicular web has attracted clearly are two separately encoded with a mechanical coil-and-spring special attention because of its yet functionally inter-linked that sticks to prey using ubiquity, pleasing geometry, character traits. electrostatic forces. The large obvious functionality and, not least, differences in the economics of its apparent structural simplicity. Why are the mechanical the two systems have led to the properties of spider webs so ecribellate webs out-competing How does the spider create the remarkable? The common garden the cribellate designs in nearly all web pattern? The typical spider spider Araneus diadematus, like ecotopes. web is a fleeting behaviour pattern other orb weavers of the solidified into a lasting record. It is ecribellate families, employs in What is spider silk? Spider silk is the spider’s inherited ‘signature’, each bead of its capture threads a not a single-protein biopolymer. In which — although unlearned — is microscopic ‘windlass’ mechanism addition to the spidroins, its main modified predictably by the that allows supreme extendibility protein constituents, the typical environment. The web is many while absorbing the high kinetic spider dragline silk contains many times the spider’s size; energy of the prey without different organic and inorganic Current Biology Vol 15 No 10 R365 components, such as Is there a commercial future for neurotransmitter peptides, glyco- webs and silks? To manufacture proteins, lipids, sugars, such silks ‘the spider’ way, we phosphates, calcium, potassium need, firstly, to copy its extrusion and sulphur. Nevertheless, at and spinning system; several present only the spidroins are patents have been taken out for considered when analysing and methods of doing this, and a modelling a silk fibre’s mechanical number of research labs are properties (except for the capture working on the problem, which is silk mechanism). Spidroin proteins far from trivial. Secondly we need are highly repetitive in their main Zygiella x-notata’s frozen behaviour to have a good spinning section and rich in the amino acids pattern. Note the spiral-free signal thread feedstock, known as the ‘dope’. alanine and glycine. leading to a silken retreat where the To this effect, spidroin genes have spider can wait, hidden and protected, a Functionally, silks can be been expressed in various typical feature for the webs of spiders in viewed as a ‘filled rubber’, in this genus. organisms that are easily cultured, which crystallites provide the such as microorganisms as well as strength and a matrix provides the throughout the duct, and that a in higher plants and even in the elasticity: in combination, these combination of solvent (water) milk of goats. Nevertheless, many two components give the silk its extrusion and subsequent important functional aspects of the toughness. Dragline silks are thus acidification helps the process of natural molecules need to be nan-composites; for example the alignment and folding. The cuticle better understood before they can major ampullate silks of Nephila of the gland’s duct facilitates the be spun for best effect. In any spiders are a composite material rapid removal of water and case, once a reliable and cheap of amorphous-disordered glycine- provides the proton pump for the expression system is up and rich α-regions interspersed with acid bath. In this way the spider running, then both the artificial crystalline-ordered domains of uses a liquid crystalline spinning spinning dopes and the extruders antiparallel alanine-rich β-regions. process which, in terms of human can be tested and optimized. Only engineering, is highly advanced. by tuning both to act in synergy How is silk spun? At present we The details of the extrusion will we be able to manufacture do not know the precise process are crucial determinants of fibres that match spider threads mechanisms by which different the mechanical qualities of the silk. and take advantage of their silk proteins fold and assemble in millions of years of co-evolution of the ‘spinning ducts’ of the various What tools are used to study feed-stocks and extrusion and diverse spider glands. Some silk? Simple stretching of a silk systems. initial insights have been gained, thread on a tensile test rig can however, into the silk pathway of provide a lot of information about Where can I find out more? one typical spider silk: the the underlying structure of the Craig, C. (2004). Spider webs and silks. dragline silk produced by the material ‘silk’. The extension curve Oxford University Press, Oxford. Foelix, R. (1996). Biology of Spiders, major ampullate glands of the allows us to look behind the Oxford University Press, Oxford. golden silk spider Nephila spp. physical parameters of modulus, Kaplan, D.L., Adams, W.W., Viney, C., Here, as in all other spider silks, strength, extensibility and and Farmer, B.L. (1994). Silk the liquid crystalline silk feedstock toughness to the molecular forces Polymers: Materials Science and Biotechnology. (ACS Books, is prepared by specialist cells in involved. The shape of the Washington). the gland wall and stored in the stress–strain curve resolves even Krink, T., and Vollrath, F. (1999). Using lumen. As with most other silks, small changes in the molecular a virtual robot to model the use of this precursor silk is then interactions of a thread, be they regenerated legs in a web spider. Anim. Behav. 57, 223–241. converted into the solid fibre by the result of modifications in the Vollrath, F., and Knight, D.P. (2004). extrusion through the tubular feedstock (molecular Biology and technology of silk taper of a duct, where the substitutions), alterations in the production. Vol 2, 873-894. In enormously long (200–400 kDa) spinning conditions (spinning Biotechnology of biopolymers: from silk molecules first unfold and are temperature and speed) or the synthesis to patents.

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