“To decorate the web or not?”


Orb weaving spiders choose to become more ornate – so some say.

Decorative white silk crosses are an ingenious tactic used by orb-weaving spiders to protect their webs from damage, a new study from the University of Melbourne has revealed.
The team, led by Dr Andre Walter and Professor Mark Elgar from the University of Melbourne’s Department of Zoology, found that orb-weaving spiders respond to severe damage to their webs by building bigger silk crosses, but if the damage is mild they don’t bother adding extra decoration.
Professor Mark Elgar said web damage is costly for spiders as a lot of nutritional resources are required to rebuild a web. “So they evolved this ingenious way to minimise unwanted damage,” he said.
“It’s much like we mark glass windows with tape to prevent people walking into them,” he said.
The team collected a group of orb-weaving spiders and left them to build their webs in the laboratory. Some of the completed webs were severely damaged, others lightly damaged and the remainder left alone. The response of the spiders was then observed.
“The fact that spiders increased their decorating activity in response to severe damage but didn’t increase their decorating following light damage suggests that the conspicuous building of silk crosses serves to make webs more visible to animals that might accidentally walk or fly into them,” Professor Elgar said.

A spider web, spiderweb, spider’s web or cobweb (from the obsolete word coppe, meaning “spider”) is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets.
Spider webs have existed for at least 140 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, southern England.
Spiders originally started producing silk for reasons other than web-making. 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 which are so famous today.

The “typical” orb-weaver spiders (family Araneidae) are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields and forests. Their common name is taken from the round shape of this typical web, and the taxon was formerly also referred to as the Orbiculariae.


Orb-weavers have eight similar eyes, legs hairy or spiny and no stridulating organs. The Araneidae family is cosmopolitan, including many well-known large or brightly colored garden spiders. There are 3,006 species in 168 genera worldwide, making Araneidae the third largest family of spiders known (behind Salticidae and Linyphiidae). The orb-weavers include over 10,000 species and make up about 25% of spider diversity.
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Image 3.

“Spider silk how sticky is too sticky?”


Modern spiders, the orb spiders, weave a variety of intricately shaped webs, but usually never get caught in it. It seems scientists have found that the silk threads that make up the web different in stickiness. The spiders travel on the non stick paths across their webs.

Orb spider's web

Orb spider's web

There is a direct correlation between the strength of a silk fiber and its stickiness.

If they made the silk threads stickier, a wriggling insect wouldn’t be able to release itself from the glue, but its struggles would ultimately break the fiber, and with it the web, ensuring its escape. If the glue is only so sticky, then the insect might be able to pull free from one capture spiral on the web, but it would then likely come into contact with the same thread again, or another and finally be too tired to struggle free. By detaching instead of breaking, a capture spiral in the web can repeatedly adhere to an insect and continue to disrupt the insect’s struggles to free itself. If the silk threads of the web were all maximumly sticky then the spider might get caught in its own web and would die.
Scientists have found that if the webs of spiders were any more sticky, they would break as they trapped insects, letting the prey escape. So a spider has to balance the stickiness of its web with how strong it is. This limits how adhesive spiders’ webs can become, forcing the creatures to evolve webs of an optimal stickiness, according to a study published in the Journal of Zoology. When tested each silk fiber on a web would release the test object it was trapping when 20 to 70% of the force required to break the fiber was applied. Seems to be a safety feature built in to thread strength and glue stickiness used to coat the threads.

Have spider webs changes over the ages?
Spiders create architecturally elegant webs by first laying down radial lines of dry silk, upon which they weave regularly spaced elastic spirals of sticky capture silk. But more than 100 million years ago, in the early Cretaceous period, spider web design changed and stickiness increased as the orb-shaped webs evolved. These araneoid orb weaving spiders seemed to have needed a better way to hold its prey.

Before then, spiders coated the spirals in their webs with puffs of dry adhesive. These dry spirals trapped insects by physically entangling around the tiny hairs known as setae on their bodies. A group of spiders living today, known as deinopoid spiders, still weave webs in this way.
During the early Cretaceous, aranoid orb weaving spiders evolved which weaved a different type of web. These spiders replaced the dry adhesive with wet droplets of glue. These are much stickier.
Maybe the stickier webs are more efficient at catching and holding prey.

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Image courtesy of wikimedia.org/wikipedia/commons/Spider_web_with_dew_drops

50 new animal species and people living in harmony Papua New Guinea.


Papua New Guinea New Species A large tree frog, Nyctimystes sp. (seen at the right) brilliant greenin color with huge black eyes, jumping spiders and a striped gecko are among more than 50 new animal species scientists have discovered in a remote, mountainous region of Papua New Guinea.

The discoveries were announced Wednesday by Conservation International, which spent the past several months analyzing more than 600 animal species the group found during its expedition to the South Pacific island nation in July and August 2008.

From the 2008 expedition, 50 new spider species, three never seen before frogs and a new gecko have now been detailed in scientific journals for the first time.. The new frogs include a tiny brown animal with a sharp chirp, a bug-eyed bright green tree frog and another frog with a loud ringing call. One of the jumping spiders is shiny and pale green, while another is furry and brown.

A Litoria frog“If you’re finding things that are that big and that spectacular that are new, that’s really an indication that there’s a lot out there that we don’t know about,” said expedition leader Steve Richards. “It never ceases to amaze me the spectacular things that are turning up from that island.”

New healthy frog species, said Craig Franklin, a zoology professor at The University of Queensland in Australia who studies frogs.

glassy green jumping spider

glassy green jumping spider

“They’re often regarded as a great can tell us that if one takes care of the environment our bioindicator species will thrive.

Researchers from Conservation International explored the region with scientists from the University of British Columbia in Canada and Montclair State University in New Jersey, as well as local scientists from Papua New Guinea.

The area the researchers explored provides a critical source of clean drinking water to tens of thousands of people living in surrounding communities and local clans rely on the region for hunting.

Man and nature live in harmony.

Anthropologist William Thomas  State University who worked with the local Hewa clan of native people reminds us that by working with local communities,  you learn a lot more because they already know so much.

Conservation International plans to conduct three more expeditions to Papua New Guinea this year, in the hopes of turning up even more new animals.

At Conservation International, our approach to preserving Earth’s biological riches is based on the premise that no organization can get the job done alone. Our steadfast belief is that together we can make a difference.



Resources

Excerpts and Images courtesy of
Scientists find new species in Papua New GuineaAP.
Photos released by  Conservation International

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