Black Widow (Latrodectus)

Black widows are notorious spiders identified by the colored, hourglass-shaped mark on their abdomens. Several species answer to the name, and they are found in temperate regions around the world.

This spider's bite is much feared because its venom is reported to be 15 times stronger than a rattlesnake's. In humans, bites produce muscle aches, nausea, and a paralysis of the diaphragm that can make breathing difficult; however, contrary to popular belief, most people who are bitten suffer no serious damage—let alone death. But bites can be fatal—usually to small children, the elderly, or the infirm. Fortunately, fatalities are fairly rare; the spiders are nonaggressive and bite only in self-defense, such as when someone accidentally sits on them.

The animals most at risk from the black widow's bite are insects—and male black widow spiders. Females sometimes kill and eat their counterparts after mating in a macabre behavior that gave the insect its name. Black widows are solitary year-round except during this violent mating ritual.

These spiders spin large webs in which females suspend a cocoon with hundreds of eggs. Spiderlings disperse soon after they leave their eggs, but the web remains. Black widow spiders also use their webs to ensnare their prey, which consists of flies, mosquitoes, grasshoppers, beetles, and caterpillars. Black widows are comb-footed spiders, which means they have bristles on their hind legs that they use to cover their prey with silk once it has been trapped.

To feed, black widows puncture their insect prey with their fangs and administer digestive enzymes to the corpses. By using these enzymes, and their gnashing fangs, the spiders liquefy their prey's bodies and suck up the resulting fluid.

Golden silk orb-weaver

The golden silk orb-weavers (genus Nephila) are a genus of araneomorph spiders noted for the impressive webs they weave. Nephila consists of numerous individual species found around the world. They are also commonly called golden orb-weavers, giant wood spiders, or banana spiders. In North America, the golden silk orb-weavers (see also Nephila clavipes) are sometimes referred to as writing spiders due to occasional zigzag patterns (stabilimenta) built into their webs, though these occur much more frequently in the webs of Argiope, such as the St Andrew's Cross spider.

Appearance and distribution:

Nephila spiders vary from reddish to greenish yellow in color with distinctive whiteness on the cephalothorax and the beginning of the abdomen. 

Like many species of the superfamily Araneoidea, they have striped legs specialized for weaving (where their tips point inward, rather than outward as is the case with many wandering spiders). 

Their contrast of dark brown/black and green/yellow allows warning and repelling of potential predators to whom their venom might be of little danger.

Golden orb-weavers reach sizes of 4.8 - 5.1 cm (1.5 – 2 in) in females, not including legspan, with males being usually 2/3 smaller (less than 2.5 cm, 1 in). The largest specimen ever recorded was a 6.9 cm (2.7 in) female N.

 clavipes (which is now debated to have been a new yet undocumented subspecies) from Queensland, that was able to catch and feed on a small-sized finch. In 2012 a large individual was photographed killing and consuming a half-meter-long brown tree snake in Freshwater, Queensland.

 Species from Taiwan have been known to reach over 5 in (130 mm), legspan included, in mountainous country.

Golden silk orb-weavers are widespread in warmer regions throughout the world, with species in Australia, Asia, Africa (including Madagascar), and the Americas. One species, N. clavipes, occurs in the United States of America, where it ranges throughout the coastal southeast and inland, from North Carolina to Texas.

Nephila spiders are the oldest surviving genus of spiders, with a fossilized specimen known from 165 million years ago.

Behavior:

Web spin:

The name of the golden silk orb-weavers refers to the colour of the spider silk, not the colour of the spider itself.

Yellow threads of their web shine like gold in sunlight. Xanthurenic acid, two quinones and an unknown fourth compound contribute to the yellow color. Experimental evidence suggests that the silk's color may serve a dual purpose: sunlit webs ensnare bees that are attracted to the bright yellow strands, whereas in shady spots the yellow blends in with background foliage to act as a camouflage. The spider is able to adjust pigment intensity relative to background light levels and colour; the range of spectral reflectance is specifically adapted to insect vision.

The webs of most Nephila spiders are complex, with a fine-meshed orb suspended in a maze of non-sticky barrier webs. As with many weavers of sticky spirals, the orb is renewed regularly if not daily, apparently because the stickiness of the orb declines with age. When weather is good (and no rain has damaged the orb web), subadult and adult Nephila often rebuild only a portion of the web. The spider will remove and consume the portion to be replaced, build new radial elements, then spin the new spirals. This partial orb renewal is distinct from other orb-weaving spiders that usually replace the entire orb web. In 2011 it was discovered that the web of Nephila antipodiana contains ant-repellent chemicals to protect the web.

Typically, the golden orb-weaver first weaves a non-sticky spiral with space for 2-20 more spirals in between (the density of sticky spiral strands decreases with increasing spider size). When she has completed the coarse weaving, she returns and fills in the gaps. Whereas most orb-weaving spiders remove the non-sticky spiral when spinning the sticky spiral, Nephila leave it. This produces a "manuscript paper" effect when the orb is seen in the sun: groups of sticky spirals reflecting light with "gaps" where the non-sticky spiral does not reflect the light.

The circular-orb portion of a mature N. clavipes web can be more than 1 meter across, with support strands extending perhaps many more feet away. In relation to the ground, the webs of adults may be woven anywhere from eye-level upwards high into the tree canopy. The orb web is usually truncated by a top horizontal support strand, giving it an incomplete look.

Adjacent to one face of the main orb there may be a rather extensive and haphazard-looking network of guard-strands suspended a few inches distant across a free-space. This network is often decorated with a lumpy string or two of plant detritus and insect carcasses clumped with silk. This "barrier web" may function as a kind of early-warning system for incoming prey or against spider-hunting predators, or as a shield against windblown leaves; it may also be remnants of the owner's previous web. At least one reference explains the suspended debris-chain as a cue for birds to avoid blundering into and destroying the web.

Stabilimenta among N. clavipes are sometimes seen in the webs of immatures nearing molt, hence the names "molting webs" or "skeleton webs" (webs with radial strands but no spiral elements).

Toxicity:

The venom of the golden silk orb-weaver is potent but not lethal to humans. It has a neurotoxic effect similar to that of the black widow spider; however, its venom is not nearly as powerful. The bite causes local pain, redness, and blisters that normally disappear within a 24-hour interval. In rare cases, it might trigger allergic reactions and result in respiratory troubles (in asthmatics) or fast-acting involuntary muscle cramps. As the genus possesses relatively strong chelicerae, the bite could leave a scar on hard tissue (such as fingers).

Parasites:

N. clavipes (and many other Nephila species) are frequently victimized by Argyrodes, a genus of very small black-and-silver spiders that are kleptoparasitic. As many as a few dozen may infest a single Nephila web to feed from the host spider's captured prey. The frequent rebuilding or abandoning of webs by Nephila may be a tactic for controlling Argyrodes. Spiny orb-weaver spiders also inhabit the webs of Nephila to obtain food.


Golden silk:

In the past there has been several efforts to produce garments from Nephila silk although none commercially viable. The last produced garment were two bed hangings that were shown at the 1900 Paris Exhibition. In 2004 a textile designer, Simon Peers, and an entrepreneur, Nicholas Godley managed in three years work and using 1.2 million Golden silk orb-weavers (collected in the wild and released some 30 minutes later after they produced the silk) to produce a shawl that was as exhibited at the American Museum of Natural History in 2009.By 2012 they managed to produce a second, bigger garment, a cape, that, together with the shawl, were exhibited at the Victoria and Albert Museum in London.

Another possible use of Nephila silk lies in tissue engineering. A study from the Medizinische Hochschule Hannover reports that processed Nephila silk is an excellent scaffold material thanks to its biocompatibility, mechanical strengths, and its property to promote cell adhesion and proliferation. In particular, the silk acts as a suitable guiding material for peripheral nerve regrowth.

Fishermen on coasts of the indopacific ocean remove Nephila webs and form them into a ball, which is thrown into the water. There it unfolds and is used to catch bait fish