March 12 – Silk Road

Today’s factismal: It took the silk from one million golden orb spiders to weave one eleven foot long piece of cloth – the only one of its kind in the world.

Though many people regard them with fear and loathing, spiders are among Nature’s most useful animals. With more than 43,000 different species known, these eight-legged members of the arthropods are native to every continent except Antarctica, and have even gone into space on several occasions. They range in size from two tenths of an inch (the Patu marplesi) to more than a foot across (the Heteropoda maxima), and inhabit every known terrestrial biome. They feed on everything from dust mites (the Patu marplesi again) to birds (the Theraphosa blondi) to cockroaches (many, many species). Though some are poisonous (most notoriously, the Latrodectus mactans) most are merely venomous (i.e., they can’t hurt you and wouldn’t if they could). But the one thing that they all have in common is their silk.

Spiders use their silk for a variety of purposes. Some species make webs with it to catch their prey. Others use it to form trapdoor homes. When food is scarce, spiders will eat their own silk. Many species use it to form long, thin streamers that the spiders use to “balloon” thourgh the air (as they did at the end of Charlotte’s Web). And one species (the Argyroneta aquatica) even uses it to make scuba gear!

The structure of spider silk (Image courtesy Xiang Wu et al.)

The structure of spider silk (Image courtesy Xiang Wu et al.)

Spider silk serves so many purposes thanks to its unique structure. Made up of proteins that are pulled out of the silk glands known as spinnerettes and into a continuous line by the spider’s legs, spider silk is stronger than steel and tougher than kevlar. Exceptionally fine and light, a strand of spider silk long enough to circle the globe would weigh just 18 ounces.And spider silk can be stretched to five times its own length before breaking.

Though the properties of spider silk have been known since antiquity, very few attempts have been made to use it mainly because of the difficulties in harvesting the silk. Once it has been woven into a web or cocoon, the silk binds to itself, forming a tangled mass when unraveled. The only way to get usable spider silk is to extract it directly from the spinnerette by means of a “milking machine”. The first such machine was made in the 1880s, and it was used to make several samples of spider silk cloth; unfortunately, these have been lost.

(Image courtesy American Museum of Natural History)

Golden Orb spiders (Image courtesy American Museum of Natural History)

Recently, two artists built a new machine and used it to harvest silk from golden orb spiders. They chose this spider because its silk has a beautiful golden hue and because the spiders are abundant in the wild. With the aid of 70 assistants, they spent four years milking more than a million spiders, getting about 80 feet of silk from each one. The silk was twisted into braids of 96 strands each, and then woven into an intricate cloth just a eleven feet long and four feet wide, on display at the American Museum of Natural History.

A cloth wovern from spider silk (Image courtesy American Natural History Museum)

A cloth woven from spider silk (Image courtesy American Museum of Natural History)

The artists did this to showcase the beauty of the silk, but scientists are interested in finding ways to put spider silks strength and structure to more practical uses. This new material could be used to make lightweight bullet proof vests for police and stronger frames for cars and bicycles; some have even suggested using it to make a space elevator. There have been several attempts to make the silk artificially, but all have failed. So for now, the scientists need to use real spiders.

And that means that they need to know what types of spiders live where. Not only will this help with research on spider silk, but it will also provide valuable information about changes in ecosystems and how spiders have adapted to lie in new biomes, such as cities. If you’d like to help with this work, then head over to the Los Angeles Spider Survey and tell them what spiders live in your area!

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