question: How does a spider not get stuck in its own Web?
comment: Not a scientist or a science major. But spiders produce 2 (or more) kinds of webs. Usually they have one that is sticky. That they get stuck in. And another one. That is stronger. It holds up the web. But isn't sticky. Spiders walk on those parts of the web
passages: Spiders do not usually adhere to their own webs, because they are able to spin both sticky and non-sticky types of silk, and are careful to travel across only non-sticky portions of the web. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not. For example, if a spider has chosen to wait along the outer edges of its web, it may spin a non-sticky prey or signal line to the web hub to monitor web movement. However, in the course of spinning sticky strands, spiders have to touch these sticky strands. They do this without sticking by using careful movements, dense hairs and nonstick coatings on their feet to prevent adhesion.
   After the radials are complete, the spider fortifies the center of the web with about five circular threads. It makes a spiral of non-sticky, widely spaced threads to enable it to move easily around its own web during construction, working from the inside outward. Then, beginning from the outside and moving inward, the spider methodically replaces this spiral with a more closely spaced one made of adhesive threads. It uses the initial radiating lines as well as the non-sticky spirals as guide lines. The spaces between each spiral and the next are directly proportional to the distance from the tip of its back legs to its spinners. This is one way the spider uses its own body as a measuring/spacing device. While the sticky spirals are formed, the non-adhesive spirals are removed as there is no need for them any more.
   Many webs span gaps between objects which the spider could not cross by crawling. This is done by first producing a fine adhesive thread to drift on a faint breeze across a gap. When it sticks to a surface at the far end, the spider feels the change in the vibration. The spider reels in and tightens the first strand, then carefully walks along it and strengthens it with a second thread. This process is repeated until the thread is strong enough to support the rest of the web.
   To open the old exoskeleton, the spider generally contracts its abdomen (opisthosoma) to supply enough fluid to pump into the prosoma with sufficient pressure to crack it open along its lines of weakness. The carapace lifts off from the front, like a helmet, as its surrounding skin ruptures, but it remains attached at the back. Now the spider works its limbs free and typically winds up dangling by a new thread of silk attached to its own exuviae, which in turn hang from the original silk attachment.
   The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.
   Section::::Types.:Orb web construction.
  
  Most orb weavers construct webs in a vertical plane, although there are exceptions, such as "Uloborus diversus", which builds a horizontal web. During the process of making an orb web, the spider will use its own body for measurements.
   Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnids, keep at least four legs on the surface while walking or running.
  
  Section::::Description.:Silk production.
   The stickiness of spiders' webs is courtesy of droplets of glue suspended on the silk threads. This glue is multifunctional – that is, its behavior depends on how quickly something touching it attempts to withdraw. At high velocities, they function as an elastic solid, resembling rubber; at lower velocities, they simply act as a sticky glue. This allows them to retain a grip on attached food particles. The web is electrically conductive which causes the silk threads to spring out to trap their quarry, as flying insects tend to gain a static charge which attracts the silk.
  
  Section::::Communal spider webs.
   The Linyphiidae generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall onto the sheet or are shaken onto it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.
  
  Section::::Evolution.
  
  Section::::Evolution.:Fossil record.
   The yellow garden spider can oscillate her web vigorously while she remains firmly attached in the center. This action might prevent predators like wasps and birds from drawing a good bead, and also to fully entangle an insect before it cuts itself loose.
   The spider, after spinning its web, then waits on or near the web for a prey animal to become trapped. The spider senses the impact and struggle of a prey animal by vibrations transmitted through the web. A spider positioned in the middle of the web makes for a highly visible prey for birds and other predators, even without web decorations; many day-hunting orb-web spinners reduce this risk by hiding at the edge of the web with one foot on a signal line from the hub or by appearing to be inedible or unappetizing.
   Some spiders have a cribellum, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost the cribellum.
   After strengthening the first thread, the spider continues to make a Y-shaped netting. The first three radials of the web are now constructed. More radials are added, making sure that the distance between each radial and the next is small enough to cross. This means that the number of radials in a web directly depends on the size of the spider plus the size of the web. It is common for a web to be about 20 times the size of the spider building it.
   Many spiders use especially fine silk called "gossamer" to lift themselves off a surface, and silk also may be used by a windblown spider to anchor itself to stop its journey. The term "gossamer" is used metaphorically for any exceedingly fine thread or fabric. Biologists also apply the term "balloon silk" to the threads that mechanically lift and drag systems.
   The hubs of orb webs, where the spiders lurk, are usually above the center, as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.
   The larger part of the odd-clawed spider's web is composed of a network of supporting threads built up to above the ground. Two lateral support threads extend from this network and are attached to vegetation or ground below. These threads are held more or less parallel to each other by several short bridge threads. The spider spins the catching ladder in between them, composed of a loose irregular zigzag of cribellate thread. The catching ladder and the supporting webs are usually built far from the retreat of the spider in the tree hollows, as far as away. The retreat and the webs are connected to each other by a single sturdy thread.
   "Araneus mitificus" builds orb webs that are characteristically missing a section. The spider does not rest on the center of the web, but instead builds a silk-lined sanctuary in a leaf at the margins. The leaf is bent at the edges and roofed with a mesh of silk. If a prey animal becomes entangled in the web, the vibrations from its struggle travel to the center of the web, then along a single long strand of silk (the signal line) positioned in the empty section. The strand is linked to the hidden spider. Once the spider feels the signal line vibrate, it will rush out to capture the prey.
   Each of the eight legs of a spider consists of seven distinct parts. The part closest to and attaching the leg to the cephalothorax is the coxa; the next segment is the short trochanter that works as a hinge for the following long segment, the femur; next is the spider's knee, the patella, which acts as the hinge for the tibia; the metatarsus is next, and it connects the tibia to the tarsus (which may be thought of as a foot of sorts); the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. The only extensor muscles in spider legs are located in the three hip joints (bordering the coxa and the trochanter). As a result, a spider with a punctured cephalothorax cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs. Although larger spiders use hydraulics to straighten their legs, unlike smaller jumping spiders they depend on their flexor muscles to generate the propulsive force for their jumps.
   After the spider has completed its web, it chews off the initial three center spiral threads then sits and waits. If the web is broken without any structural damage during the construction, the spider does not make any initial attempts to rectify the problem.
   Some spiders manage to use the signaling-snare technique of a web without spinning a web at all. Several types of water-dwelling spiders rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.
  
  Section::::Uses.:Uses by humans.
   The spider stays in the middle of the lower orb web hanging upside down. When it feels threatened, however, it will run to the edge of the web and hide among the vegetation and debris. The spider has a sanctuary at the edge of the web surrounded by dead leaves which it can use to camouflage itself. The male of the species can also inhabit the same web as the female.
   This spider builds a funnel-shaped web to catch its prey. It usually consists of a multitude of stressed silk threads spun over a flat surface (such as a window sill) near any corner, with a funnel-like structure reaching for the corner, in which the spider would typically reside (hence the name). These webs can become quite large if undisturbed. They act like cord strings, helping the spider glide over them, and once a prey stumbles into the web, it will quickly get attacked, then dragged inside the funnel part and eaten, but very rarely stored underneath the structure.
   "Theridiosoma gemmosum" constructs a small orb web. The radii do not run directly to a central hub as with other orb webs, but are first joined into groups of two or three before combining to meet in the middle. A single thread runs from the centre to a nearby support, and is held by the spider. While the spider is holding this thread the tension pulls the web into a conical shape, described as "like an umbrella turned inside out". When a prey item hits the web, the spider releases the tension, causing the prey to become more enmeshed.
  
  Section::::Taxonomy.
   The net-casting spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter and also avoids the energy loss of weaving a large orb web.
   Spiders in the genus "Deinopis" catch their prey in an unusual fashion. They first spin a small upright rectangular cribellate web. This is then detached from its supporting threads and held horizontally above the ground by the spider's long front two pairs of legs while the spider hangs almost vertically. Passing prey is then captured by dropping the "net" over it.
  
  Section::::Eyes.
  
presuppositions: A spider's web is made solely out of sticky silk. Spiders will get stuck in their own web since they are sticky.
corrections: There are parts of a spider's web that aren't sticky that spiders walk on. Spiders also produce non-sticky webs that they walk on.
raw_presuppositions: A spider's web is made solely out of sticky silk. Spiders will get stuck in their own web since they are sticky.
raw_corrections: There are parts of a spider's web that aren't sticky that spiders walk on. Spiders also produce non-sticky webs that they walk on.