Spider- The Master Spinner

Spider- The Master Spinner

Spiders are found every-where, up in the Himalayas, below the sea level, in deserts, on tree tops and even in burrows. Approximately 32,000 species of spiders have been described, and this probably represents only a small portion of the actual number. Spiders by mistake are the most feared and maligned of nature’s small creatures- but at the same time the most fascinating also.
Only a dozen or so types of spiders are dangerous to man. On the other hand nearly most of them are involved in keeping the incalculable hordes of harmful insects in check.

Many consider spiders as insects, but they are not. Spiders are closely related to scorpions and ticks. Spider population is very large. Brest-owe calculated that an acre of undisturbed grassy meadow contained 2,265,000 spiders. Many features (adaptations) of spider make them interesting, animals-their feeding habits, their utilization of venom, the powerful vision, the modified hands (pedipalps) foe copulation in males and their amazing capacity to secrete silk and spin webs.

Spider’s spinning habit and hanging on to the web is attributed to Greek mythology. An artful weaver named Arachn impudently challenged goddess Athena to a contest. Later, shamed and mortified by her own conceit, Arachne hanged herself. The goddess in a moment of compassion, brought Arachne back to life, transformed her into a spider and made her nose into a web. In order to preserve the memory of this lesson, the goddess commanded Arachne and her descendents to hang on to the web. Thus these classical are subscribed Arachnids.

The size of spiders range from small pin heads (0.5mm ) to the size of dinner plates (12cms). The larger ones are mygalomorphs like tarantulas, bird spiders or monkey spiders. The convex head (carapace) bears eight eyes anteriorly. A pair of chelicerae, pedipalps and four pairs of legs are the usual appendages of a spider. Chelicerae is of moderate size with a fang at the end. Pedi alps are short and leg- like but in the male they are modified to form copulatory organs. The tip of pedipalp is knob-like and resembles a boxing glove; The legs are formed of eight joints. Abdomen is globe-shaped and usually unsegmented. On each side of the abdomen, openings called spiracles are present through with the spider breathe. At the end of the abdomen a modified structure called spinneret is found which spins the web. Each spinneret is a short conical structure bearing many openings from the silk glands. The glands themselves are largely located in the posterior half of the abdomen.

Spiders feed mainly on insects. The prey either is pounced upon by members of more active groups or is caught on the silken snare. Hunting forms include wolf spiders, fisher spiders, jumping spiders and tarantulas: Prey is detected by tactile and visual stimuli and in some families like wolf spiders and jumping spiders leap on the prey by sudden extension of legs, which result from sudden elevation of blood pressure. Hunting spiders lay down a dragline while ground spiders tie up their prey by running around them.

Spider web is made of silk which is a protein. It is emitted as a liquid and hardening result not from exposure to air but from actual drawing-out process itself. Silk plays an important role in the life of the spider. All families of spiders do not build webs. The silk s sometimes used as a dragline which acts as a safety line similar to that used by mountain climbers. Another function of silk is to protect eggs by forming cocoons.

The silk thread made by the spider is as thin as one-millionth of an inch. The threads are elastic and can stretch more than twenty percent and are stronger than steel wire of the same diameter.

Construction of an orb web by a spider is a remarkable feat. Web building is dependent upon many factors like silk supply, behavioral state of spider and appetite. Web building spiders are aerialists of the family Araneidae. They usually have slender legs. To move about in the web, the lines are hooked by a small middle claw which lies between the two large claws of the legs, the form of threads is determined by spinnerets- clusters of tiny nuzzled jets from which the spider draws the silk with its hindmost pair of legs. The mesh size of the web depends on the size of the spider and the potential prey size. The web is replaced periodically. The sticky nature of the web is lost in a week, the old silk is eaten and the protein is resecreted as new silk. Sometimes the web is replaced every night.

Curved claws and thick barred hairs at the tip of each leg permit orb-web spiders to race across silken lines. They avoid entanglement in their own snares by walking only on the dry radial strands and shunning the sticky spiral threads.

Web builder spiders are very sensitive to vibration: They can determine from thread vibrations the size and location of trapped prey. Investigations show that they respond to strange vibrations also. In a certain experiment, the web of the spider Argiope was touched by a vibrating tuning fork. Instantly the spider rushed across the strands and furiously assaulted the quivering metal. With her legs she pulled silken stream from her spinnerets and in seconds the prongs of the fork were bound tight. Spiders are unable to discern vibrations. The tuning fork or a thrashing insect, the response is the same.

Spiders have highly complex precopulatory or sexual behavior patterns. The partners identify each other by chemical and tactile cues. On encountering a dragline, a male spider can understand whether it is produced by his own relatives and that to from a matured female spider. A chemical substance called pheromone is responsible for this. Like-wise the female also responds to a variety of cues from males. The male plucks the strands of the webbing which can be detected by the female. Sometimes, as in the case of hunting spiders, the male directly pounces on the female and palpates her body with pedipalps to stimulate her.

The female lays her eggs in several batches. Silk is spun over the eggs to form a case called cocoon for protection. The spider ling’s hatch inside the eggs, by ballooning process they get dispersed too far off places.

Right on tomorrow, watch a spider on your window pane beginning to lay a foundation for her web. The very next day you can see, a geometrically perfect web has been made and the spider resting in the centre after the marathon effort. With ablow from your nose, you can destroy it, but again the following day morning you can see a more compact web the spider has made. This spider does not lose battle or lose heart as it does not have one. But then imagine how much destruction you have done with a blow from your nose to this Nature’s art of perfection. If this task of web spinning is given to you, you will mess up and get enmeshed in thread knots as man is yet to attain that standard of perfection as that of a spider.

Article By:P.R.Venkitaraman, St.Albert's College