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Orb Weavers and the Wonderful World of Webs

written by: KennethSleight•edited by: Donna Cosmato•updated: 6/23/2011

With over 10,000 unique species, the Araneidae Family (orb weavers) of spiders comprises over 25 percent of the total variety on Earth. They are known for their iconic oval webs; a standard of Halloween décor, but there are some very interesting variations on the web from one type to another.

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    Orb Weaver Web The orb weaver spider gets its name from both the shape of the web it weaves and the shape of its abdomen. Though most orb weavers do spin relatively circular webs as they grow older each one develops web characteristics that are intrinsic to the particular species.

    When you see a web with a spider at its center, you are most likely looking at a female of the species as the males spend most of their time traveling from place to place in search of a mate. It’s not that males don’t spin webs, they do, they just don’t spend much time in them. They are also much smaller than the females, which makes them doubly hard to spot.

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    Circular and Spiral Webs

    Almost all orb weaver spiders weave circular webs with concentric circles radiating from the center out to the edges. The spiders start their webs by shooting a line between two strong anchor points (the branches of a tree, the side of a garage and a bush, etc.). This line is shot in a downward angle, and the spider climbs down to the center of the line and shoots a second line opposite the first creating an upside down Y-structure. The spider then begins creating a circular pattern using the original central Y-structure of the web as a base. These silk strands are not sticky, as opposed to common belief, and are simply the base structure of the web.

    Once the spider has completed the structural layer of the web, it goes to work on the capturing mechanism. A second layer of silk -this is the sticky one - is laid down in circles between the existing structure. This is accomplished by walking with one set of legs on the interior circle and one on the next structural circle. The abdomen, being directly between, lays the sticky line.

    Most webs are vertical although a few spiders make horizontal webs to accommodate the particulars of the environment (this happens quite often in late May and early June in the United States, as mayflies and June bugs emerged from the ground).

    Have you ever noticed that orb weavers have practically spotless webs? It isn’t because they are great housekeepers that spend their days pulling debris off the sticky web but because they spin a new web every night. Why aren’t there a bunch of abandoned webs around? The orb weavers eat their old webs in the early morning (before the sun comes up) and recycle the material into new a web for the next night.

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    Life Cycle

    Orb weaver spiders are short lived, lasting only a year for most species, which begins when the young hatch in the early spring. From the moment they are born, they are capable of weaving webs and tracking down prey. These juvenile spiders are rarely seen due to their relatively small size and tendency to make webs in dense foliage to avoid predators.

    Orb weavers are generally seen in the late summer and early fall when they have reached full adult size and have started to engage in the mating process. Males will come to a female web and carefully pluck the strings to announce themselves. Failure to do this could mean they would end up as a tasty snack instead of a potential mate. The female will then lay a clutch of eggs (100 or more) and allow the males in to fertilize them. Males die shortly thereafter. The females live until the end of fall and die long before their young hatch to start the process over.

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    Are Orb Weavers Dangerous?

    Although coming face to face with a large orb weaver spider might cause one to startle, there shouldn’t be any long term fear. These spiders are skittish, and their first reaction when threatened is to run away. If they do bite, it is only as a last resort (usually when someone tries to pick them up). They are venomous and their bite feels like a bee sting but it isn’t fatal or even particularly painful (unless you have an allergic reaction, which is extremely rare).

    In fact, the orb weaver should be treated with the utmost respect as it helps to rid your yard and garden of unwanted pests like mosquitoes, flies and other winged bothers. The largest members of the family have been known to feast on hummingbirds and the unfortunate frog or toad that gets tangled in a web.

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    Families

    Araneidae Family

    Gastercantha Orb Weaver There are over 3000 species in this family of orb spider. They are identified by a large golf ball shaped abdomen or brightly colored oval abdomen except for the Micrathena and Gastercantha species, which do not fit this typical look but are equally easily identified by their unique shapes (tending to look like seeds for camouflage.

    Within the family Araneidae is the subgrouping Argiopes, which are known for adding a specialized zig-zag pattern to the center of their webs. Although the reason for this is unknown, it is speculated that this both deters predators by making the spider look larger and enhances the capture rate of the web by adding more sticky surface area.

    Nephilidae – Golden Orb Spiders

    Golden Orb Weaver These 75 species used to be part of the Araneidae family but due to their large size, the golden hue of their silk, female reproductive plug and the unique behavior of the male after mating they were moved into their own subgroup. These spiders are the largest of the orb weavers and reach sizes up to two inches (five centimeters) across in the abdomen region. They often weave webs of over two feet across and are the most common “garden spiders" in the United States.

    Males, instead of wandering off to die after mating, stand guard to deter other males from trying to mate with the female. Another unique Nephilidae aspect is that females have a plug that blocks secondary insemination so that once her eggs are fertilized a second male will not be able to mate with her.

    Tetragnathidae - Long Jawed Orb Weavers

    Long Jawwed Orb Weaver This particular sub family consists of spiders with exceptionally long jaws. They spin smaller webs than their cousins and do not fit them with signal lines or avenues of retreat. These spiders don’t spin tightly woven webs but use only a few radials and interior circles to catch their favorite prey, moths and butterflies. They also prey on mosquitoes and dragonflies near their chosen wetland habitat.

    Uloboridae – Cribellate Orb Weavers

    These spiders are both non-venomous and produce non-sticky filament silk. They rely on the tight weave of their webs to snare flying insects by using the prey’s own momentum to draw the web in around them.

    Orb Weavers that Don’t build Webs

    Bolas spiders create a small globule of web and cast it out like a fishing net to snare flying insects. They are often referred to as angler or fisher spiders. They initially attract the prey by using pheromones that mimic the mating scents of female moths. When the prey is within range, the globule net is launched with deadly accuracy.

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    Orb weaver spiders are some of the most successful creatures on the planet. Their adaptations and use of a web for catching prey allow them to remain in a static area for most of their lives and thus allows them to adapt even further to the specifics of a locale. When an orb weaver enters your garden, take care not to disturb its web so that it may remain and pick off the insects that really bug you.

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    References

    Matjaž Kuntner, Introduction to Nephilidae", http://www.nephilidae.com/intro.htm

    Author Unknown, “Identification, Images, & Information For Insects, Spiders & Their Kin For the United States & Canada", http://bugguide.net/node/view/1972

    Author Unknown, Animal Corner, “Orb Weaver Spiders", http://www.animalcorner.co.uk/venanimals/ven_spidorb.html

    Author Unknown, “Garden Orb-weavers", http://www.minibeastwildlife.com.au/Garden%20orb-weavers.htm

    Orb Weaver Web photo courtesy of Energetic Spirit @ flickr, http://www.flickr.com/photos/nperlapro/1347300641/sizes/m/in/photostream/ under CC BY 2.0

    Golden Orb Weaver photo courtesy of h3_six @ flickr, http://www.flickr.com/photos/hach3/2483369486/sizes/m/in/photostream/ under CC BY 2.0

    Gastercantha Photo courtesy of Clicksy @ flickr, http://www.flickr.com/photos/29412527@N04/3688538992/sizes/m/in/photostream/ under CC BY 2.0

    Long Jawwed Orb Weaver Photo courtesy of yokohamayomama @ flickr, http://www.flickr.com/photos/yokohamayomama/5732596035/sizes/m/in/photostream/ under CC BY-SA 2.0