This female orbweaver's body measures 15mm, or a little less than 5/8 inch. Leg span = 35mm (1-3/8")

Araneidae is a large family of spiders, nearly all of which spin symmetrical orb webs. In many species, males are much smaller and less brightly colored than the females. Orb weavers have eight eyes arranged in two rows, and females typically have a large, distended abdomen which may overhang the carapace, and which may have conspicuous bumps (tubercules) or spines, e.g. Micrathena genus.

The eight legs of orb weavers are usually well-endowed with spines, with three tarsal claws the spider uses to grip its silken strands.

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Orb weaver spiders often add stabilimenta, or heavy zig-zagging portions, to their webs. Stabilimenta are conspicuous lines or spirals of silk, included by many diurnal spiders at the center of their otherwise cryptic webs. It has been shown spider webs using stabilimenta catch, on average, 34% fewer insects than those without. However, webs with the easily-visible markings are damaged far less frequently by birds flying through the web. It is an evolutionary tradeoff the spider can influence every time it builds a new web. The inclusion of stabilimenta is influenced by many factors, including prey density and web location.  You can read the scientific study at Behavioral Ecology magazine.

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The Orb Weaver Larinioides cornutus, commonly called the furrow, or foliate spider, is very common on human structures, especially under eaves and porches. (They live on my back porch by the dozens, males and females alike in their smallish-orb webs.) Unlike their larger sisters amongst the weeds, these beautiful little rascals are strictly nocturnal, hiding in crevices or in foliage retreats from dawn till dusk.
 

Marbled Orb Weaver Spider - Araneus marmoreus
Most orb weavers spin spiraling webs on support lines that radiate outward from the center; the plane of the web may be vertical or horizontal or somewhere in between. Many orb webs are built on human structures, parallel to walls.

Are Orb Weaver spiders dangerous? Short answer: No. Spider Bite Symptoms: Mild burning or itching, no worse than a bee sting. You'd have to work pretty hard to be bitten by one of these spiders. An orb-weaver spider bites only defensively.

They can dish it out, but can they take it? This unfortunate orb weaver has become host to some sort of parasitic larva - you can see the white, worm-shape just behind the spider's head, on top of the cephalothorax under the overhang of the abdomen. Some have suggested it may be a mantid larva or perhaps some sort of wasp larva. It could also be a parasitic fly in the family Syrphidae,  Tachinidae, or Phoridae (the flies that infect the domestic honey bees). 

This from the Atlantic Magazine online:
"Consider Polysphincta gutfreundi, a parasitic wasp that grabs hold of an orb spider and attaches a tiny egg to its belly (sic). A wormlike larva emerges from the egg, and then releases chemicals that prompt the spider to abandon weaving its familiar spiral web and instead spin its silk thread into a special pattern that will hold the cocoon in which the larva matures. The “possessed” spider even crochets a specific geometric design in the net, camouflaging the cocoon from the wasp’s predators."

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