A classic circular form spider's web
Opadometa fastigata weaving the web. See the silk coming from the spinneret glands located at the tip of the abdomen.
Spiral orb webs in Karijini, Western Australia
Garden Orbweaver with beetle prey caught in its web
A spider web, spiderweb, spider's web, or cobweb (from the archaic word coppe, meaning "spider") is a structure created by a spider out of proteinaceous spider silk extruded from its spinnerets, generally meant to catch its prey.
Spider webs have existed for at least 100 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, southern England.
Many spiders build webs specifically to catch insects to eat. However,
not all spiders catch their prey in webs, and some do not build webs at
all. "Spider web" is typically used to refer to a web that is apparently
still in use (i.e. clean), whereas "cobweb" refers to abandoned (i.e.
dusty) webs. However, the word "cobweb" is also used by biologists to describe the tangled three-dimensional web of some spiders of the Theridiidae
family. While this large family is known as the cobweb spiders, they
actually have a huge range of web architectures; other names for this
spider family include tangle-web spiders and comb-footed spiders.
Silk production
Clearly visible spider silk production
Zygiella orb web
Infographic illustrating the process of constructing an orb web
Spider web covered in hoar frost
When spiders moved from the water to the land in the Early Devonian period, they started making silk to protect their bodies and their eggs.
Spiders gradually started using silk for hunting purposes, first as
guide lines and signal lines, then as ground or bush webs, and
eventually as the aerial webs that are familiar today.
Spiders produce silk from their spinneret glands located at the tip of their abdomen.
Each gland produces a thread for a special purpose – for example a
trailed safety line, sticky silk for trapping prey or fine silk for
wrapping it. Spiders use different gland types to produce different
silks, and some spiders are capable of producing up to eight different
silks during their lifetime.
Most spiders have three pairs of spinnerets, each having its own
function – there are also spiders with just one pair and others with as
many as four pairs.
Webs allow a spider to catch prey without having to expend energy
by running it down.
Thus it is an efficient method of gathering food. However, constructing
the web is in itself an energetically costly process because of the
large amount of protein required, in the form of silk. In addition,
after a time the silk will lose its stickiness and thus become
inefficient at capturing prey. It is common for spiders to eat their own
web daily to recoup some of the energy used in spinning. The silk
proteins are thus recycled.
The tensile strength of spider silk is greater than the same weight of steel and has much greater elasticity. Its microstructure is under investigation for potential applications in industry, including bullet-proof vests and artificial tendons. Researchers have used genetically modified mammals to produce the proteins needed to make this material.
Types
Argiope sp. sitting on web decorations at the center of the web
There are a few types of spider webs found in the wild, and many
spiders are classified by the webs they weave. Different types of spider
webs include:
- Spiral orb webs, associated primarily with the family Araneidae, as well as Tetragnathidae and Uloboridae
- Tangle webs or cobwebs, associated with the family Theridiidae
- Funnel webs, with associations divided into primitive and modern
- Tubular webs, which run up the bases of trees or along the ground
- Sheet webs
Several different types of silk may be used in web construction, including a "sticky"
capture silk and "fluffy" capture silk, depending on the type of
spider. Webs may be in a vertical plane (most orb webs), a horizontal
plane (sheet webs), or at any angle in between. It is hypothesized that
these types of aerial webs co-evolved with the evolution of winged
insects. As insects are spiders' main prey, it is likely that they would
impose strong selectional forces on the foraging behavior of spiders.
Most commonly found in the sheet-web spider families, some webs will
have loose, irregular tangles of silk above them. These tangled obstacle
courses serve to disorient and knock down flying insects, making them
more vulnerable to being trapped on the web below. They may also help to
protect the spider from predators such as birds and wasps.
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.
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.
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.
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.
Australian garden orb weaver spider, after having captured prey
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.
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.
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.
Uses
A soldier ant finds itself entangled in the web of a garden spider.
Some species of spider do not use webs for capturing prey directly, instead pouncing from concealment (e.g. trapdoor spiders) or running them down in open chase (e.g. wolf spiders). The net-casting spider
balances the two methods of running and web spinning in its feeding
habits. This 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 such as the wolf spider. It also avoids the energy loss
of weaving a large orb web.
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.
Uses by humans
Cobweb paintings, which began during the 16th century in a remote valley of the Austrian Tyrolean Alps,
were created on fabrics consisting of layered and wound cobwebs,
stretched over cardboard to make a mat, and strengthened by brushing
with milk diluted in water. A small brush was then used to apply watercolor
to the cobwebs, or custom tools to create engravings. Fewer than a
hundred cobweb paintings survive today, most of which are held in
private collections.
In traditional European medicine, cobwebs were used on wounds and cuts and seem to help healing and reduce bleeding. Spider webs are rich in vitamin K,
which can be effective in clotting blood. Webs were used several
hundred years ago as pads to stop an injured person's bleeding. The effects of some drugs can be measured by examining their effects on a spider's web-building.
Spider web strands have been used for crosshairs or reticles in telescopes.
Development of technologies to mass-produce spider silk has led to manufacturing of prototype military protection, medical devices, and consumer goods.
Adhesive properties
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.
Communal spider webs
After severe, extensive flooding in Sindh, Pakistan, many trees were covered with spider webs.
Occasionally, a group of spiders may build webs together in the same area.
Massive flooding in Pakistan during the 2010 monsoon drove spiders above the waterline, into trees. The result was trees covered with spider webs.
The communal spider web at Lake Tawakoni State Park
One such web, reported in 2007 at Lake Tawakoni State Park in Texas, measured 200 yards (180 m) across. Entomologists believe it may be the result of social cobweb spiders or of spiders building webs to spread out from one another. There is no consensus on how common this occurrence is.
In Brazil, there have been two instances of a phenomenon that
became known as "raining spiders"; communal webs that cover such wide
gaps and which strings are so difficult to see that hundreds of spiders
seem to be floating in the air. The first occurred in Santo Antônio da Platina, Paraná, in 2013, and involved Anelosimus eximius individuals; the second was registered in Espírito Santo do Dourado, Minas Gerais, in January 2019, and involved Parawixia bistriata individuals.
Outside influences
Certain drugs, including caffeine, affect the way spiders build webs.
Administering certain drugs to spiders affects the structure of the
webs they build. It has been proposed by some that this could be used as
a method of documenting and measuring the toxicity of various
substances.
Low gravity
It has been observed that being in Earth's orbit has an effect on the structure of spider webs in space.
Spider webs were spun in low earth orbit in 1973 aboard Skylab, involving two female European garden spiders (cross spiders) called Arabella and Anita, as part of an experiment on the Skylab 3 mission.
The aim of the experiment was to test whether the two spiders would
spin webs in space, and, if so, whether these webs would be the same as
those that spiders produced on Earth. The experiment was a student
project of Judy Miles of Lexington, Massachusetts.
After the launch on July 28, 1973, and entering Skylab, the spiders were released by astronaut Owen Garriott into a box that resembled a window frame. The spiders proceeded to construct their web while a camera took photographs and examined the spiders' behavior in a zero-gravity
environment. Both spiders took a long time to adapt to their weightless
existence. However, after a day, Arabella spun the first web in the
experimental cage, although it was initially incomplete.
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The first web spun by the spider Arabella in orbit
The web was completed the following day. The crew members were
prompted to expand the initial protocol. They fed and watered the
spiders, giving them a house fly.
The first web was removed on August 13 to allow the spider to construct
a second web. At first, the spider failed to construct a new web. When
given more water, it built a second web. This time, it was more
elaborate than the first. Both spiders died during the mission, possibly
from dehydration.
When scientists were given the opportunity to study the webs,
they discovered that the space webs were finer than normal Earth webs,
and although the patterns of the web were not totally dissimilar,
variations were spotted, and there was a definite difference in the
characteristics of the web. Additionally, while the webs were finer
overall, the space web had variations in thickness in places: some
places were slightly thinner, and others slightly thicker. This was
unusual, because Earth webs have been observed to have uniform
thickness.
In popular culture
Spider webs play a crucial role in the children's novel Charlotte's Web. Webs are also featured in many other cultural depictions of spiders.
In films, illustration, and other visual arts, spider webs may be used
to readily suggest a "spooky" atmosphere, or imply neglect or the
passage of time. Artificial "spider webs" are a common element of Halloween decorations. Spider webs are a common image in tattoo art, often symbolizing long periods of time spent in prison, or used simply to fill gaps between other images.
Some observers believe that a small spider is depicted on the United States one-dollar bill, in the upper-right corner of the front side (obverse),
perched on the shield surrounding the number "1". This perception is
enhanced by the resemblance of the background image of intertwining fine
lines to a stylized spider web. However, other observers believe the
figure is an owl.
Artificial spider webs are used by the superhero Spider-Man to restrain enemies and to make ropes on which to swing between buildings as quick transportation.
The World Wide Web is thus named because of its tangled and interlaced structure, said to resemble that of a spider web.
The notable tensile strength of spider webs is often exaggerated
in science fiction, often as a plot device to justify the presence of
artificially giant spiders.
