Na­ture’s drapes of spun lace

Sus­pended in fields and hedgerows, the lacy art­work of the spi­der’s web is an ethe­real but ef­fec­tive trap

Landscape (UK) - - Contents - Words: Di Wardle

In the still­ness of an early Oc­to­ber morn­ing, a lilac bush ap­pears to glis­ten in the first rays of sun­shine. Strung be­tween its branches is a del­i­cate spi­der’s web, its filmy threads cov­ered in droplets of dew that sparkle in the light. El­e­gant cir­cles of silk spi­ral be­tween a wheel of fil­a­ments that ra­di­ate from its cen­tre, in a form of ephemeral beauty. At the heart of this cre­ation sits the ar­chi­tect of this stun­ning piece of nat­u­ral en­gi­neer­ing: a garden spi­der, wait­ing for her prey. It has taken the spi­der a mere 20 min­utes to spin her web, a task she per­forms anew each morn­ing. She builds it us­ing only the sense of touch, her long, sen­si­tive legs draw­ing out silk through a se­ries of tubules, called spin­nerets, on the tip of her ab­domen. In it, she catches the mos­qui­toes, green­fly and other in­sects on which she feeds. Al­though both male and fe­male garden spi­ders spin webs from birth, the male stops do­ing so when he reaches sex­ual ma­tu­rity, at ap­prox­i­mately eight weeks. “Garden spi­ders are re­spon­si­ble for most of the orb webs that we see in our gar­dens. These are the round webs peo­ple typ­i­cally think of as spi­der webs,” says Lawrence Bee, of the Bri­tish Arach­no­log­i­cal So­ci­ety. “The name is ac­tu­ally a bit mis­lead­ing, as garden spi­ders are found in many places, such as woods, heaths and clifftops; any­where, in fact, where there are trees or grasses from which they can hang their webs.”

Other de­signs

Garden spi­ders are just one of be­tween 30-40 species in Bri­tain that spin elab­o­rate and in­tri­cate orb webs. But there are other types of web, per­haps not as el­e­gant, but just as ef­fec­tive in trap­ping in­sects. The sim­plest form is a tube web. These are built by spi­ders, such as the tube spi­der, in rock crevices or holes in walls. They line these fis­sures with silk be­fore spin­ning trip wires that ra­di­ate out around the mouth of the open­ing. The spi­der sits inside with a leg on each trip wire, alerted to vi­bra­tions from pass­ing prey. Tan­gle webs, so called be­cause they are a mass of tan­gled up silk threads, are spun by spi­ders in­clud­ing the cel­lar spi­der and daddy long legs spi­der. Hid­den among the mesh of silk are taut trip wire threads stuck to an at­tach­ment point with a drop of glue-type gel. The strug­gles of any in­sect that gets stuck in the glue will break the trip thread. As it springs up, it pulls the in­sect into the net-like web. Sheet webs, spun by the fa­mil­iar money spi­der and com­mon house spi­der, work in a sim­i­lar way. This time, a thin sheet of silk is strung be­tween two walls or blades of grass, with taut lines of thread stretch­ing above the web. Should an in­sect col­lide with these threads, it is knocked down into the sheet be­low. Lace webs are made of a very fine ‘woolly’, blue-grey silk, which the spi­der

“The bird a nest, the spi­der a web, man friend­ship” Wil­liam Blake, ‘The Mar­riage of Heaven and Hell’

‘back­combs’ with a leg as it emerges from the spin­neret. The mi­nus­cule hooks formed snag any in­sects that land on the web. These webs are of­ten spun in the cor­ners of win­dows and un­der flow­er­pots, by the window lace-weaver spi­der.

Silk weaver

The silk pro­duced by spi­ders is finer than a hu­man hair, but weight for weight is stronger than steel. It is also in­cred­i­bly re­silient and elas­tic, able to stretch up to four times its length with­out break­ing. Largely made up of two pro­teins, fi­broin and sericin, it is pro­duced as a liq­uid in glands in the ab­domen. These are at­tached to the spin­nerets that open onto the sur­face. As the liq­uid silk trav­els through the spin­nerets, it so­lid­i­fies into a thread, the thick­ness of which is con­trolled by a valve which can widen or nar­row. All male spi­ders pro­duce at least three types of silk, and fe­males four. “Spi­ders use silk in lots of dif­fer­ent ways, and some can pro­duce as many as seven dif­fer­ent types,” says Lawrence. “Dragline silk, the long strands you of­ten see spi­ders hang­ing from, is par­tic­u­larly strong and elas­tic, and acts as a safety rope, al­low­ing spi­ders to in­ves­ti­gate their sur­round­ings or to make a quick get­away. Silk is also used to wrap up prey, and fe­males pro­duce a spe­cial type which they use to make an egg case. Young spi­ders use very fine gos­samer silk in dis­per­sal. And, of course, silk is used to spin a web, which it­self will con­tain more than one kind of silk.”

Build­ing bridges

Garden spi­ders usu­ally build their webs be­tween 3-6½ft (1-2m) from the ground, strung be­tween a frame­work of dragline-strength flex­i­ble silk. They fol­low the same pat­tern for ev­ery web they spin. “Each morn­ing, the fe­male spi­der will climb to a high point, the top of a bush or a fence post, and re­lease a thread of silk,” he ex­plains. “This will drift in the breeze, even­tu­ally catch­ing on some­thing; an­other bush, per­haps. The spi­der will sense this, pull on the line to tighten it and then walk along it. As she goes, she re­in­forces it with a sec­ond strand to cre­ate a strong bridge.” The first stage of build­ing work com­plete, the spi­der now spins an­other thread of silk be­low the bridge line and at­taches it at both ends. “The cen­tre point of this line will be­come the cen­tre of the new web,” says Lawrence. “She goes to this point and then drops down on a line of thread, pulling the up­per line down to cre­ate a ‘Y’ shape. These three lines, all made of dragline silk, form the first three ra­dial threads of the web. Their ends are at­tached to frame­work threads that she has po­si­tioned around the sides, joined to the an­chor­ing bush or post.” One by one, more ra­dial threads are added. They are evenly spaced, the gap be­tween them never so wide that the spi­der can­not cross it. As a re­sult, a spi­der’s web is al­ways in pro­por­tion to the size of

the spi­der mak­ing it, and webs are big­gest in au­tumn when spi­ders are fully grown. “Ra­dial threads com­plete, the spi­der goes back to the cen­tre and spins a spi­ral of finer silk be­tween them, from the cen­tre out,” he ex­plains. “This is ac­tu­ally only a tem­po­rary struc­ture, and the spi­der uses it to walk on dur­ing con­struc­tion. Hav­ing reached the out­side of the web, she then turns round and goes back the other way. This time, she spins a per­ma­nent spi­ral, with the loops closer together, eat­ing the tem­po­rary one as she goes. As she lays down the new silk, she se­cretes drops of glue and twangs each thread with her leg. The droplets scat­ter down the threads, cre­at­ing a sticky sur­face that will trap her un­for­tu­nate prey.”

Ef­fec­tive trap

Once the web is com­plete, the spi­der will usu­ally po­si­tion her­self on a plat­form of criss-crossed silk threads she builds in the cen­tre, hang­ing up­side down from the un­der­side of the web. She will know if prey has been snared. “Her legs are so sen­si­tive that she can pick up tiny vi­bra­tions,” ex­plains Lawrence. “Any­thing strug­gling will get her at­ten­tion, and she will move across the web to­wards it. A seed or some­thing static that might have been blown into the web will be ig­nored. Hav­ing three claws and spe­cial brush-like hairs on the end of her legs, she doesn’t stick to the web her­self.” When she reaches her quarry, the spi­der pierces it with her fangs and in­jects venom from a gland un­der the jaw. The in­sect is im­mo­bilised and dies in sec­onds. As more in­sects hit the web, along with pollen, dust and other de­bris, it can lose its stick­i­ness. It may also be dam­aged in strong winds. To make sure she does not go hun­gry, the spi­der will spin a new web ev­ery morn­ing, eat­ing the old one to re­cy­cle the silk pro­teins.

Growing pains

As spi­ders grow, they must shed their skins as their rigid ex­oskele­ton can­not grow with them. Moult­ing is very stren­u­ous, and the spi­der may even die dur­ing the process. Hang­ing from a thread of dragline silk, the spi­der in­creases its heart rate so much that the rise in blood pres­sure causes the outer cov­er­ing of the head and tho­rax to lift. The sides of the ab­domen then part, and the spi­der grad­u­ally wrig­gles its way out of its skin. It may take hun­dreds of twists and turns to do this, legs of­ten prov­ing a par­tic­u­lar prob­lem. Once free, its tis­sues ex­pand to their new size and the ex­oskele­ton hard­ens once more. The old skin, called the ex­u­vium, dan­gling on its line of silk, may eas­ily be mis­taken for a dead spi­der.

The next gen­er­a­tion

The re­pro­duc­tion process of a spi­der be­gins when an eight-week-old male wan­ders in search of a fe­male. When he finds a web with a likely part­ner, the male plucks and vi­brates the threads in a spe­cial rhythm so that he is not mis­taken for prey. Grad­u­ally, he edges to­wards the fe­male. If she is re­cep­tive, mat­ing takes place, usu­ally in mid sum­mer. The male spins a small web on which he de­posits sperm. He then ab­sorbs the sperm into his two sen­sory or­gans, called pedi­palps, and places them in the

“A big bud of moon hangs out of the twi­light, Star-spi­ders spin­ning their thread Hang high sus­pended, with­outen respite Watch­ing us over­head.” D H Lawrence, ‘Li­ai­son’

fe­male. He dies soon af­ter mat­ing. As win­ter ap­proaches, the preg­nant fe­male lays as many as 100 eggs, which she wraps in a pro­tec­tive silk co­coon. Ini­tially, she may stand guard over her eggs, but, weak­ened by the birthing process, she will die be­fore they hatch the fol­low­ing May. “If you look care­fully in the garden in spring, you may see a mass of tiny spi­ders sur­rounded by a cloud of threads,” says Lawrence. “This is the re­mains of their co­coon, and if you prod the threads, count­less spi­der­lings will run out, scat­ter, and then shoot back together again. It’s fas­ci­nat­ing to watch.” Af­ter a cou­ple of days, the spi­der­lings be­gin to seek new hori­zons. They climb up­wards, scal­ing a stone or a blade of grass, and re­lease a tiny strand of gos­samer silk. Ready to spin webs so small they are prac­ti­cally in­vis­i­ble to the hu­man eye, they float away on the breeze, and the cy­cle be­gins once more.

Hav­ing cre­ated a wheel of ra­dial threads, the spi­der links them with a spi­ral of finer spun silk, start­ing from the cen­tre of the web and cir­cling out­wards.

A grassy field draped with sheet webs, which dip like ham­mocks, ready to catch the spi­der’s prey.

Del­i­cate lace webs are of­ten found in the cor­ner of old win­dows and have a bluish tinge.

A tube web around the open­ing of a hole in a wall with threads spread­ing out from the en­trance to catch out in­sects.

Like yarn pulled taut be­tween spools, sheets of web catch the early au­tumn light.

Morn­ing dew set­tles on a tan­gle web, en­velop­ing plants in a mesh of tan­gled threads.

Af­ter climb­ing to the top of stems on which to at­tach her web, the fe­male spi­der cre­ates a net-like cur­tain be­tween them.

Ris­ing wa­ter lev­els force spi­ders to re­treat to higher plants, cov­er­ing them in a silken canopy of thread.

Droplets hang from fine threads like strings of glit­ter­ing beads adorn­ing the leaves.

Lawrence Bee is lead au­thor of Bri­tain’s Spi­ders: A Field Guide, and com­mit­tee mem­ber of the Bri­tish Arach­no­log­i­cal So­ci­ety.

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