Spider Anatomy (Part I)

Just like any other biological creatures on earth, a spider also has an anatomical structure. Each part of its anatomy has a designated purpose for its special function. Without at least one of the spider's anatomical parts, the spider may not exist at all.

A spider is an amazing creature on earth. It's really worth a while to take a look at them closely and try to comprehend their nature. You will come to understand how they magnificently struggle into existence despite the dangerous environments around them. You will also come to fully rationalize the very reason why spiders do what they do and understand why as well they have certain features in them. When you get to know what they are for and how they tangibly function for a spider's existence, you will be amazed how much there is to understand about spiders. There's certainly more to them than just the domestic bugs you normally get rid of along with termites and cockroaches.

There are many ways to foster the appropriate appreciation and interest for spiders and one way to do about that are to know more about them, starting with learning their anatomy.

The External Body

The common anatomy of a spider is a body that is comprised in two parts: the abdomen, where the silk producing glands and the spinnerets are located, and the prosoma or cephalothorax which is where the head, eyes, chelicerae are located. A pedicel is a portion of the spider body that conjunct the two parts. A spider size could range from about less than 1 millimetre or .04 inches, to 10 centimetres or 4 inches in length. But there are other spider species, particularly the tarantulas, which can grow as large as 10-12 inches. In fact the tarantula species is where the largest spiders are.

Often called a hard shell of an invertebrate, the exoskeleton is the only thing responsible of protecting the insides of the spider. It covers its entire body. The materials that comprise a spider's exoskeleton is mainly based on some protein compounds with tough fibers namely chitin. The exoskeleton is basically stratified cuticles of the protein compounds convoluted into one another, and the arrangement of the piles often improves the protection it gives to the spider and as well as its flexibility. The cuticle also provides a desiccation mechanism for the spider and also the framework to the various muscles that a spider possesses. There's a difference however, between the cuticle found in the abdomen and the cephalothorax. The cephalothorax cuticles are relatively harder than that of the abdomen. Each time a spider molts, it sheds away the old cuticles and develops a new one to cover itself.

The Cephalothorax

This part of the spider's body is comprised of a variety of structures and appendages. The first part is chelicerae that are used by the spider to bite its prey and for initial digestion. Another part near the chelicerae is the poison glands where the venom is located which are usually used to immobilize their victims, especially to smaller species of spiders. Another part is the pedipalps, leg-like appendages which also happen to look like their ninth and tenth legs but considerably small in size. And also the initial four rear legs of the spider and the 6-8 eyes.

Mouth Parts

To most spiders, they are able to grab hold of their prey by using their two appendages near their mouth. These things are called the chelicerae. Actually, the chelicerae more or less resemble a pocket knife to a spider. The chelicerae contain a pair of fangs as well that when a spider prepares to take a bite or uses it for some other reasons, swings out from its former position and stabs right into the preys body. Nearby the fang of a spider is the poison glands' duct opening. The fangs actually serve as needles for the venom that a spider will inject to its victim in order immobilize it.

Other purposes of chelicerae are to dig out holes in the ground and to carry preys around from one place to another. But the purposes may differ on the species of the spider.

Poison Glands

Perhaps referred to as the bread and butter of the spider race, a spider's venom is its main tool for capturing and subduing its prey. Despite the spider's sheer force (particularly in the case of larger spiders like tarantulas), they would still need to subdue their victims with venom to ensure no escape. When to be used, the chelicerae muscles would then contract squeezing the glands in order to produce the toxins needed, it would then come out from the duct opening located near the fangs and then to the prey.

Palps and Legs

Right behind a spider's chelicerae are a pair of palps. These segmented looking limbs are not only used for feeding but also for feeling its prey before eating it. Most male species of spiders use their palps to inject sperms to females during intercourse. Adjacent to the pair of palps are the initial four pairs of legs of a spider. These legs are quite hairy. The hair in the legs of a spider is used to detect vibrations from prey or to foresee any imminent danger in the environment. Basically, the legs of a spider serve as its antennae. This protects the spider from all sorts of danger every time.

Sensory Organs

Most species of spiders are nocturnal and they will most likely do all the hunting at night. As a result to that innate characteristic, spiders have developed keener senses than its visual aspects and in return their eyes are also less developed. There are other species of spiders however, that has more developed eyesight and mainly uses it to capture their prey. Apart from the hairs found in their palps and legs, a spider also has a lot of hairs in its feet which are more often used to taste its prey.

A lot of spiders only have four pairs of simple eyes. Simple eyes are eyes that only have single lenses. These parts are located in the front area of the cephalothorax. There are certain species of spiders however, like the brown recluse which only has six.