They are seen everywhere: Orb webs are in the grass, on shrubbery, hanging from trees, between rocks, along woods paths, or in and on buildings. They may be less than an inch or more than six feet in diameter. Spiders may sit in the middle or hide under vegetation at its edge, but they are always in contact with the threads that tell them when a visitor arrives. If the intruder is a prey item, the spider rushes out of its resting place and immobilizes the prey by biting it. If another spider, the response will vary depending on the species and sex of the visitor. If a predator or animal too large to be trapped by the sticky web, the spider will run off the web or move deeper into its resting area.
These spiders construct their webs with silk produced in spinnerets at the posterior end of the body. Larger webs are made of thicker and stronger silk. When prey is captured, the spider first binds it to the web, but after the prey is consumed, it is cut out of the web and dropped to the ground. After some time, webs become damaged and their glue dries up. Spiders do not repair these webs. Though the webs of orb weavers are impressive fabrications, spiders lack the finesse to assess the extent of a damaged section, determine what needs to be done to fill the gap, and perform the necessary actions. By producing a completely new web, there is nothing to think about: she simply starts from scratch. Thus, many spiders make new webs almost every night. They begin by eating the old web threads to recycle the proteins when making the new web.
Making the web
First, the spider frames out the web edges and constructs a central platform of non-sticky silk. From this platform, she drops to the edge and glues a new radial spoke to it. She then walks up the last spoke to the platform, pulls the new spoke taught, and glues it to the platform.
When she can no longer drop down to the supporting edge, she walks along the last spoke, glues the next spoke to the outer support, walks back, pulls the new spoke up, and attaches it to the platform. In this manner, she makes a web framework that looks somewhat like a bicycle wheel with a platform where the axle would be, an outer edge, and radial spokes between. These components never contain glue, as they are used by the spider to move around the web without getting caught herself. These strands are five times stronger than steel threads of the same weight.
Sticky Threads
Finally, she attaches the circular webbing that captures the insects This webbing is dotted with about thirty glue droplets per inch. These droplets are essential for capturing prey. If it were not for them, many insects could extricate themselves from the web before the spider was able to immobilize them. Also, if not glued down, larger insects could injure the spider by beating on her as they flail their wings and legs in an attempt to escape. The glue ensures the prey becomes entangled in the sticky threads and is held fast until the spider can dispatch it.
Sheet Silk
Sheet silk is another type of silk spiders produce. After the prey is captured, the spider produces a sheet of several strands at the same time and rapidly spins the insect around to encapsulate it. After being enclosed in a straight jacket of silk, the insect cannot escape or injure the spider. Spiders often stop spinning several times to bite the prey, injecting more poison and digestive enzymes.
Sheet silk is also used to make patterned areas in some spider webs, notably those in the Aranea genus. These sometimes have the shape of a Z or X. These patterns are not decorative, however. They reflect ultraviolet light that insects can detect and fly toward. By making these inclusions in the web, the spider adds a lure to attract insects much as a bug zapper light does.
Both uses of sheet silk are seen in the photograph of the golden garden spider wrapping up a grasshopper.
Spider Venom
Having no mandibles, spiders cannot chew. After wrapping the prey, the spider retreats to her resting area where she will wait for the digestive enzymes in her venom to work its course. When the spider returns to the cocoon, she removes some of the silk, and uses her pharynx to suck the predigested material out of the prey and and pump it into her stomach. The prey rapidly becomes an empty shell. The spider then severs the threads that hold the cocoon in the web and lets it drop to the ground.
Although some spiders are dangerous to humans and pets, most are not. It is better to avoid them and leave them alone than to indiscriminately kill these beneficial citizens of our world.
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