Question

Will you consider spinning the web by a spider as an intrinsic behavior? Why or why not?

Answer 1

Hint: Spiders belong to the class Arachnida, phylum Arthropods. The body of the spider is divided into cephalothorax and abdomen. The head is devoid of antennae. Cephalothorax possesses a pair of chelicerae, a pair of pedipalpi (both are used in feeding), and four pairs of legs. Respiration occurs with the help of the trachea or book lungs. Excretion occurs either by malpighian tubules or coxal gland or both. Guanine is an excretory product.

Complete answer:
The spiders show a unique behavior of spinning webs. Spiders produce silk threads to build their webs. The silk is produced in the silk glands. The silk glands are large and present in the 10th to 11th segments. Each gland is lined by a single layer of silk producing cells, which pass through spinning tubes. In different species, the silk glands vary. There are six kinds of film glands, in orb spiders, each liberating a special kind of silk.
The silk threads have high elasticity and maximum tensile strength, and can be thick or thin, dry or sticky, beaded or smooth. The silk is composed of fibroin protein. Silk threads may be flat or cylindrical with varying diameter. When the spider begins to construct the web, the thread is liquid, but they dry quickly in the air.
The spinnerets, present in the posterior part of the abdomen, are specialized structures for spinning silk. The spinnerets tips are membranous and covered by barbs and hairs, and the base is stout. Cribellium (accessory spinning organ) and calamistrum (brush-like hairs on the metatarsus of the 4th leg) are specialized structures present to work with the spinnerets.
When a spider begins to spin a web, it releases a silk thread which is anchored to some object- a branch, a corner of a room, a doorframe- wherever it builds its web. Spiders move back and forth to add more threads, strengthening the web and creating a pattern. Lines radiating from the center of the web to outward are called “radial lines”. Threads that go circularly around the web are called orb lines.
Instinctive or intrinsic behaviors are those which are not learned or practiced. Spinning the web is an intrinsic behavior of spiders because nobody has to teach them how to do it. They are born knowing how.

Note:
The spiders spin their webs to catch the dinner. When an insect flies into a spider's web, it gets stuck on the sticky threads. When a spider catches a prey in its sticky strands, the spider approaches the trapped insect, and uses its fangs to inject venom. The venom either kills or paralyzes the prey. Not all spiders spin webs for food, some don’t build webs at all.