Monday, March 9, 2009

Spider's Necrotic Venom

Spider venoms work on one of two principles; they are neurotoxic or necrotic. Neurotoxit works by attacking the nervous system, necrotic works by attacking tissues surrounding the bite, and in some cases, attacking vital organs and systems.

Necrotic’s spiders are found in the family Sicariidae, a family which includes both the recluse spiders and the six-eyed sand spiders. Some species in this family are more venomous than others. Bites by spiders in this family can produce symptoms ranging from minor localized effects, to severe dermonecrotic lesions, up to and including severe systemic reactions including renal failure, and in some cases, death. Even in the absence of systemic effects, serious bites from Sicariidae spiders may form a necrotising ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. The damaged tissue may become gangrenous and eventually slough away. Initially there may be no pain from a bite, but over time the wound may grow to as large as 10 inches (25 cm) in extreme cases. Bites usually become painful and itchy within 2 to 8 hours, pain and other local effects worsen 12 to 36 hours after the bite with the necrosis developing over the next few days.
Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely more severe symptoms occur including hemolysis, thrombocytopenia, and disseminated intravascular coagulation. Debilitated patients, the elderly, and children may be more susceptible to systemic loxoscelism. Deaths have been reported for both the brown recluse and the related South American species L. laeta and L. intermedia.

Numerous other spiders have been associated with necrotic bites in the medical literature for examples are hobo spider and yellow sac spider. However, the bites from these spiders are not known to produce the severe symptoms that often follow from a recluse spider bite, and the level of danger posed by each has been called into question.


Thursday, March 5, 2009

Spider's Webs Grouping

There is no coherent relationship between the classification of spiders and the web’s types, but there are few types of spider web found, and many spiders are classified by the webs they weave.

Several different types of silk can be used in web construction, including a "sticky" capture silk and "stuffed" 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 between them. More commonly found on 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 getting caught in the web below. They can also help protect the spider from predators such as birds and wasps. Different types of spider webs are: Spiral orb webs, Tangle-nets or cobwebs, funnel-webs, Tubular webs, sheet webs, dome or tent webs. Now you know about spider webs, hope you don’t trapped on it.


Wednesday, March 4, 2009

Web of Spiders

Everybody knows that spiders related with web. There is no coherent relationship between the classification of spiders and the web’s types. Species in the same genre can build very similar or very different webs.

Nor is there much correlation between spiders’ classification and chemical composition of their silks. Convergent evolution at web building, in other words, the use of similar techniques for remotely related species, is "rampant”.

No orb-web design and spinning behaviors that produce them have received very little attention from arachnologists, although the majority of spiders do not build orb webs. Basic radial and spiral sequence visible in orb-webs and the "sense of direction" needed to build them may have been inherited from common ancestors of most spider groups. It used to think that the sticky orb web was a result of evolutionary innovation in the diversification of Orbiculariae.

Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders. Non-orb spiders have more than 40% more species and are four times as abundant as orb-web spiders. Their greatest success may be due to sphecid wasps, which are often the dominant predators on spiders, much prefer to attack spiders with flat webs.


Tuesday, March 3, 2009

The Brief Desciption of Spider

This is the basic lesson before you know deeper about spider, we start from desciption. Spiders are air-breathing arthropods chelicerate have eight legs, fangs and chelicerae modified injecting poison. In their bodies the usual arthropod segments are fused into two tagmata, cephalothorax and abdomen, along with a small, cylindrical pedicel. In all but the most primitive, the Mesothelae, spiders have most of the central nervous systems of all arthropods, as all nodes are merged into one mass in the cephalothorax. Spiders do not have the extensor muscles of the extremities and spread rather than hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk of up to six types of silk glands in their abdomens. Spider webs vary widely in size, shape and amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms and producing tangled cobwebs spiders are more abundant and varied ob-spiders. Spider-like arachnids with silk-producing spigots appear in the Devonian period some 386 million years ago, but apparently these animals lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years and are very similar to the most primitive to survive, Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic period, before 200 million years ago.

Spiders was described as vegetarian species in 2007, but all other known species are predators, preying mostly on other insects and spiders, though a few large species also birds and lizards. Spiders use a wide range of strategies to capture prey, the nets catch on sticky, sticky balls with lassoing imitating the prey to avoid detection, or running down. Most detect prey primarily by detecting the vibrations, but are active hunters acute vision, and the hunters of the genus Portia show signs of intelligence in the choice of tactics and the ability to develop new ones. Spiders "casings are too narrow to take solid food and liquidize by flooding with digestive enzymes and grinding with the foundations of their pedipalps, as they have no true jaws.

Male spiders identify themselves by a variety of complex courtship rituals to avoid being eaten by the females. Males of most species survive a few links, mainly limited by its short life. The women weave silk egg cases, each of which can contain hundreds of eggs. The females of many species care for their young, for instance, about carrying them or by sharing food with them. A minority of species are social, building community networks that can be anywhere from home to some 50,000 individuals. Behavior ranges from precarious social tolerance, as in the aggressive widow spiders, a cooperative hunting and sharing food. Although most spiders live in more than two years, mygalomorph tarantulas and other spiders may live up to 25 years in captivity.

While the venom of some species is dangerous to humans, scientists are now investigating the use of spider venoms in medicine and no pollutants such as pesticides. The spider silk offers a combination of lightness, strength and elasticity that is higher than that of synthetic materials and the spider silk genes have been inserted in mammals and plants to see if they can be used as a silk factory. As a result of its wide range of behaviors, spiders have become common symbols in art and mythology, which represent different combinations of patience, cruelty and creativity.