June 30, 2014 Stealthy Spiders Have Stood the Test of Time
King Robert the Bruce I was born at Lochmaben Castle in 1274. He was Knight and Overload of Annandale. In 1306 he was crowned King of Scotland and henceforth tried to free Scotland from the English enemy.
After being defeated at a battle, Bruce escaped and found a hideout in a cave. Hiding in a cave for three months, Bruce was at the lowest point in his life. He thought about leaving the country and never returning.
While waiting, he watched a spider building a web in the cave’s entrance. The spider repeatedly fell down yet finally it succeeded in building its web. So Bruce decided also to retry his fight and told his men: “If at first you don’t succeed, try, try and try again.”
Spiders are remarkable. They have been on our planet for 400 million years. The story of how 34,000 species of spiders inhabit our Earth is intriguing.
Spiders are found almost everywhere – from the Arctic Islands to dry deserts; from the tops of tropical mountains to the valley bottoms of temperate forests.
Spiders have devised an ingenious ballooning method whereby standing on tip-toes facing the wind their abdomen reels out silk, like a fisherman playing a game-fish – allowing them to travel up to 100 kilometers (60 miles) on one silk line.
They’ve even conquered remote Pacific Islands by hitchhiking on driftwood.
Spiders can go up to 200 days without food.
Some spiders like to wrap their prey in silk before eating them. It is not that dissimilar to some people, who like to wrap their lunch in a soft-shelled taco.
Water spiders live underwater by enclosing their abdomen in an air bubble. Orb spiders have impressive webs. Wolf spiders are ruthless hunters. Pirata spiders hunt insects on top of water. Crab spiders ambush prey by moving sideways. Jumping spiders pounce prey like a cat. Spitting spiders spew venom that glues helpless prey to the ground prior to lethal paralysis. Bolas spiders throw a sticky drop at male Spodotera moths fooling them to believe it’s a female scent before throwing a bolas web over top of them.
The body of a spider is made up of two parts: the anterior and the posterior joined in the middle with a thin stalk.
The anterior contains the heart, 8 eyes in two but sometimes three rows, often two types of lungs, one pair of biting poisonous fangs (which can act like hands), one pair of leg-like pedipalps (some times known as pinchers), four pairs of walking legs and the central nervous system. Two protective plates cover the anterior.
The posterior is responsible for digestion, circulation, respiration, excretion, reproduction and silk production.
The blood (more correctly called hemolymph) of spiders is rich with copper pigments giving it a bluish colour. Blood cells have important roles in: blood clotting, wound healing and fighting off infections. One molecule of spider hemolymph has more than 600 amino acids or the building blocks of protein.
About 30 species of spiders contain poison lethal to humans. Black widows, the Australian funnel-web, the American brown, two kinds of European water spiders and the very aggressive South American ctenids spiders contain venom that attacks and discombobulates the human central nervous system. If bitten an antidote must be taken in order to obviate a fatality.
In most cases, however, spider bites are much less dangerous to humankind than poisonous stings of bees, wasps and hornets.
Spider poison is designed to paralyze its prey – mainly insects. Defensive bites against large animals, including humans, are only secondary.
The poison is administered through the fangs. Either the spider crunches its prey immediately or after its been wrapped in silk, or it sucks out the insides of its prey through the fang holes – much like a straw draining the last drop from a soda bottle.
Some people loath spiders. Perhaps it’s because they are extremely hairy. Tarantulas are the hairiest of all spiders. They use their hair as a defense mechanism. They are able to brush off clouds of abdominal hair with their hind legs. Each hair is covered by hundreds of microscopic hooks that cause severe itching when in contact with skin especially the nose and eye region.
Spider feet are covered in hairs. Each hair, in turn, may have up to 1,000 extensions. About 160,000 contact points enable spiders to walk perpendicular or upside down on glass.
Like humans the behaviour of spiders is controlled by their central nervous system. Spiders rely upon mechano-receptors like touch, vibrations and air currents to make a living. Spiders have a sense of taste, smell and they exhibit a capacity to learn.
Most spiders are active during the night and depend upon touch and smell to assist them in finding a mate and recognizing prey and predators. Over 1,000 hairs on the front set of legs are very sensitive to chemical odors.
All spiders have the ability to produce silk. Spider silk is awesome. It is stronger than bone, tendon or cellulous (wood) only steel – smelted iron-ore is stronger. Spider’s silk is strong because it is made up of multiple proteins, and water, which gives it incredible elasticity.
A spider’s silk dragline would have to be about 90 kilometers (54 miles) long before it ruptured under its own weight.
Only web spiders, as the name infers, produce snares or webs to capture prey. Ground spiders must constantly wander in search of prey.
There are a number of different webs: sheets, frames and orbs. The spider hides at one end of the web, rushing out only when prey has blundered into the snare.
Orb webs are commonly seen in backyards and forests throughout North America and elsewhere.
Radial threads converge in a central spot. Frame threads delineate the web and serve as the starting point for radial threads. Both types of threads act as a scaffolding for the sticky catching spiral.
The spider feels the vibration of the ensnared prey. It is usually able to rush out on the exact radial thread leading straight to the insect.
Spiders are extraordinary engineers. In just a half-hour at night, with the sense of touch not sight, they are able to spin 20 meter (66 feet) of silk web. The entire web weighs no more than between 0.1 and 0.5 milligrams yet it is able to easily hold a spider weighing in excess of 500 milligrams.
Spiders thrived in the ancient Carboniferous forests some 300 million years ago. Fossil records show that orb webs were used 100 million years ago. About 300 species have been described from the Tertiary period from samples of well-preserved Baltic and Dominican ambers (fossilized tree resin) 40 million years ago.
Spiders are worthy of our admiration; they have stood the test of time on our blue planet.
Earth Dr Reese Halter is a broadcaster and biologist. His upcoming book is called Shepherding the Sea: The Race to Save Our Oceans.
Text © by Dr Reese Halter 2014. All rights reserved.