Here, a money spider Tenuiphantes sp. Spider silk is one of the most versatile materials on Earth. Actually a protein created by special organs known as spinnerets, spider silk can be used for transportation, shelter, courtship, and all kinds of creative ways to trap prey.
Some spiders can produce more than one type of silk. A common orb-web, for example, may contain at least four different kinds, each adding a different component, such as strength, flexibility, and stickiness.
Equipped with such a versatile material, spiders have evolved to create a wondrous assortment of webs. There are horizontal sheet webs that catch falling prey and vertical latticework webs that intercept flying prey.
Black widow webs are messy affairs, while funnel webs and lampshade webs can resemble three-dimensional sculptures. Spiders in the Theridiosomatidae family build conical webs that can fire a spider at nearby prey like a slingshot, while ogre-faced spiders nab their meals with hand-held nets. Read about the spider that uses its web to shoot itself faster than a rocket. When ants or crickets brush up against one of these tendrils, the line snags the prey and then snaps, drawing the helpless creature up into the air where it will dangle until the redback decides to eat it.
On the other side of the spectrum, there are spider silks that reflect ultraviolet light and appear blue at certain angles. In the tropics, there are even spiders in the Nephila genus that infuse their silks with carotenoids, which, when the sun hits them, makes the webs seem as if they were dipped in liquid gold.
Bolas spiders skip web-building altogether. These clever creatures lure moths in close with pheromones and then swat the insects out of midair with a single piece of sticky, weighted silk that they swing around like a mace. Gnaphosids shoot silk at their prey like Spiderman. Of the close to 50, spider species known to science, most do not produce webs at all, says Craig. It tugs to make sure the silk strand is truly attached, then it pulls out new silk and attaches the strand to whatever it is perched on and starts gathering up the snagged strand, pulling itself towards the endpoint, all the while laying out new silk behind it.
That new silk is the first planar line. The spider may do this 20 times, creating a network of dry not sticky silk lines arcing in all directions. The spider cuts away the 13 lines that it won't use. Then the spider starts to spin its web, a relatively simple and predictable process. It begins at the outside and works its way in, attaching segment by segment with its legs, creating concentric circles and ending with a center spiral of sticky silk that traps much-needed prey—all the energy invested in making the web depletes protein stores.
The sticky stuff merely immobilizes the prey. A few families of spiders have developed an alternative mode of offense: the sticky-silk wrap attack. At the end of each spinneret is a collection of spigots, nozzle-like structures.
A single silk thread comes out of each. Jan explains, 'Although it looks a bit like an icing nozzle, the silk is pulled out by gravity or the spider's hind leg. The silk is liquid when it's inside the spider.
Before it is extruded out of the spinneret, cribellate silk first passes through a sieve-like structure called the cribellum. Spiders that make this type of silk also have a row of specialised leg bristles called the calamistrum, which combs the silk out and gives it the different, woolly texture.
Spiders then follow various patterns of activity to construct their webs, depending on what species it is. It's fascinating to watch. Although webs are the most well-known use for spider silk, not all spiders make webs to catch their prey. In fact, less than half of the 37 spider families in Britain do. Other spiders, such as crab spiders in the family Thomisidae, are 'sit and wait' predators - for example Misumena vatia lurks on flower heads, waiting to ambushing visiting insects.
Others, such as jumping spiders in the family Saltidae, actively follow their prey and catch it by leaping on it. Some spiders even invade other webs to find their food.
The pirate spiders, of which there are four UK species in the genus Ero , go onto another spider's web and mimic the behaviour of its prey to lure the spider closer. When the web's owner investigates, the pirate spider attacks. However, even spiders that don't make webs have uses for silk, including creating moulting platforms, sperm webs for males, and retreats.
Jan adds, 'Jumping spiders, for example, make little silken cells in which to hide in during the day - a bit like a sleeping bag. That avoids the need to take in lots of data and parse it later.
And then there are animals that appear to offload part of their mental apparatus to structures outside of the neural system entirely. Female crickets, for example, orient themselves toward the calls of the loudest males. They pick up the sound using ears on each of the knees of their two front legs. These ears are connected to one another through a tracheal tube.
Sound waves come in to both ears and then pass through the tube before interfering with one another in each ear. The system is set up so that the ear closest to the source of the sound will vibrate most strongly. In crickets, the information processing — the job of finding and identifying the direction that the loudest sound is coming from — appears to take place in the physical structures of the ears and tracheal tube, not inside the brain. Once these structures have finished processing the information, it gets passed to the neural system, which tells the legs to turn the cricket in the right direction.
Extended cognition may partly be an evolutionary response to an outsized challenge. According to a rule first observed by the Swiss naturalist Albrecht von Haller in , smaller creatures almost always devote a larger portion of their body weight to their brains, which require more calories to fuel than other types of tissue. It works for mammals from whales and elephants down to mice; for salamanders; and across the many species of ants, bees and nematodes. And in this latter range, as brains demand more and more resources from the tiny creatures that host them, scientists like Wcislo and his colleague William Eberhard , also at the Smithsonian, think new evolutionary tricks should arise.
In , Eberhard compared data on the webs built by infant and adult spiders of the same species. As a result, they might be expected to slip up while performing a complex task. Perhaps the spiderlings would make more mistakes in attaching threads at the correct angles to build a geometrically precise web, among other measures.
Just as octopuses appear to outsource information-processing tasks to their tentacles, or crickets to their tracheal tubes, perhaps spiders outsource information processing to objects outside of their bodies — their webs. If spider and web are working together as a larger cognitive system, the two should be able to affect each other. Consider a spider at the center of its web, waiting. Many web-builders are near blind, and they interact with the world almost solely through vibrations.
Sitting at the hub of their webs, spiders can pull on radial threads that lead to various outer sections, thereby adjusting how sensitive they are to prey that land in those particular areas. As is true for a tin can telephone, a tighter string is better at passing along vibrations.
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