by Janet Spencer
The word “spider” comes from the Old English words “spithra” and “spinnan” meaning “to spin.” Come along with Tidbits as we admire spider webs!
AN AMAZING SUBSTANCE
• Spider silk is incredibly elastic, able to stretch up to 130% of its original length. It’s five times stronger than a similar strand of steel. It’s chemically inert, stable at high temperatures, waterproof, and non-allergenic.
• Silk starts out in the spider’s body as a sort of liquid protein. As the spider squirts it out, it passes through a narrow tube which forces all of the protein’s molecules to align in the same direction, which turns the silk strand into a solid, rod-like, semi-crystalline thread as soon as it hits the air. Look at a thread of silk under a powerful microscope and you will see that some of the protein rods are straight and some are curved. Together they act like links in a chain. When the silk is stretched, the curved sections straighten out. When the stress is released, they snap back to their original curved shape. The structure of the thread is so incredibly sturdy that the only thing that will fragment it is to boil it in acid.
• Some types of webs last for years, such as funnel webs built by house spiders which can shelter many generations of spiders.
• Other webs such as the iconic wheel-shaped webs built by orb weaver spiders are fragile and easily damaged by wind and rain, while their sticky properties are affected by pollen and dust. Orb weavers often rebuild their entire webs every single night, requiring that they manufacture 20 yards of silk.
• Some species, such as tarantulas, use their silk to build trap doors, and to line their underground lairs with silk tubes. When an insect gets too close, tarantulas can spring out, grab the prey, and drag it inside.
• The diving bell spider spends its entire life underwater—the only spider known to do so. It survives underwater because of its waterproof airtight bell-shaped web, which it anchors to aquatic plants, with lines of silk extending up toward the surface. The spider climbs these lines of silk and lifts its rear out of the water to collect air bubbles around the tiny hairs that line its legs and abdomen. Carefully holding the air bubbles between its back legs, it descends back to its bell-shaped web and places the bubbles inside to form one large bubble. The bell can also take up dissolved oxygen from the water.
• The female Darwin’s bark spiders build enormous webs—some extending more than 80 feet (24 m)—across rivers and lakes. By building their super-strong web across the water like a bridge, they can catch large insects like dragonflies that quickly swoop and rise along the water’s surface. The female will spend days building and reinforcing the bridge lines that she casts across rivers to anchor the web on each bank, and repairing damage to the center caused by large insects.
• 70 people spent four years collecting golden orb spiders from telephone poles in Madagascar, while another dozen workers used hand-powered machines to carefully extract about 80 feet (24 m) of silk filament from each of the arachnids before letting it go. The resulting 11-foot by 4-foot (3.5 m) cape is the only large piece of cloth made from natural spider silk existing in the world today. By the end of the project, they had extracted silk from more than 1 million female golden orb spiders. No one has been able to produce commercial quantities of spider silk. Silkworms are much easier to work with because they are docile and slow, whereas spiders are quick and independent. In addition, silkworms eat mulberry leaves, which are easier to attain than live flies.
• Spiders have been observed changing the size and shape of their web depending on what prey is available. They build small webs with a fine mesh to catch small flies, and larger wide-meshed webs to catch termites.
• One type of assassin bug sits on the edge of a spider web and tweaks the strands of silk in just exactly the same way that a small innocent trapped bug would. When the spider approaches, the assassin bug pounces and eats the spider instead.
• One type of tiny spider discovered in Taiwan survives not by eating insects but by stealing and eating pieces of other spider’s webs.
• Balloon spiders, which throw silk strands into the air in order to be lofted by the wind, have been found floating in the air more than 200 miles (322 km) from land. Weather balloons have found them floating at 30,000 feet (9 km) above the surface of the earth.
• Why don’t spiders stick to their own webs? Some spiders are covered with a special oil that prevents them from sticking to their webs. Others spike the strands of their web with tiny drops of sticky glue spaced exactly one footstep apart, so the spider can run up and down the strands, placing its feet between the drops. Some make some of their strands sticky and other strands not sticky and then they run only on the non-sticky strands.
• Two Yale biologists noticed that certain strands in webs had a slightly different appearance from the rest of the web. On a hunch, they put the webs under ultraviolet light and found a distinct pattern in each web that showed up best under UV wavelengths. Wondering why, they took two webs from the same spider and placed them in opposite ends of a Y-shaped chamber. One of the webs was bathed in light which included the UV wavelength, but the other had UV blocked out. A swarm of fruit flies was released, and most headed straight into the ultraviolet web. The researchers theorize that ultraviolet-reflecting strands are invisible to insects, who see them as clear blue sky and fly into them assuming nothing is there.
• A scientist recorded the effect of drugs on spiders. Drugs such as marijuana and phenobarbital made the spiders lazy and imprecise in their web-building; spiders on amphetamines made smaller webs with a distorted pattern; mescaline produced odd angles in webs; caffeine caused spiders to build webs so weird they couldn’t really be called webs; and LSD made spiders construct square webs, zig zag webs, and webs that could never hold their weight.