Spiders: Amazing webmasters can live just about anywhere
Love them or loathe them, you have to admire spiders for their range and ingenuity.
Thu, Jul 01, 2010 at 09:08 AM
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 tiptoes facing the wind, their abdomen reels out silk, like a fisherman playing a gamefish. This allows them to travel up to 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 on prey like a cat. Spitting spiders spew venom that glues helpless prey to the ground prior to a lethal paralysis. Bolas spiders throw a sticky drop at male Spodoptera moths, fooling them into believing it’s a female scent before throwing a 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, eight eyes in two, sometimes three rows, often two types of lungs, one pair of biting poisonous fangs (which can act like hands), one pair of leglike pedipalps (also 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 in copper pigments, giving it a bluish color. Blood cells play 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 aggressive South American ctenid spiders contain venom that attacks and discombobulates the human central nervous system. If bitten, humans must take an antidote to avoid death.
In most cases, however, spider bites are much less dangerous to humans than the 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 it has 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.
They are hairy critters
Some people loathe spiders. Perhaps it’s because they are 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 itching when in contact with skin, especially the nose and eye region.
Spider feet are covered in hair. 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 behavior of spiders is controlled by a central nervous system. Spiders rely upon mechano-receptors like touch, vibration and air currents to make a living. Spiders have a sense of taste and smell, and they exhibit a capacity to learn.
Most spiders are active during the night and depend upon touch and smell to assist in finding a mate and recognizing prey and predators. Over 1,000 hairs on the front set of legs are sensitive to chemical odors.
Silk stronger than bone
All spiders can produce silk. Spider silk is awesome. It is stronger than bone, tendon or cellulose (wood). Only steel — smelted iron ore is — stronger. Spider 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 54 miles long before it ruptured under its own weight.
Only web spiders, as the name implies, produce snares or webs to capture prey. Ground spiders must constantly wander in search of prey. Web varieties include 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 usually can 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 can spin 66 feet of silk web. The web weighs no more than 0.1 to 0.5 milligrams, yet it can 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.
Dr. Reese Halter is a conservation biologist at Cal Lutheran University, public speaker and founder of the international conservation institute Global Forest Science. Follow him @ twitter.com/DrReeseHalter.