Spiders Essay Research Paper Spiders can be

Spiders Essay, Research Paper

Spiders can be found in all environments throughout the entire

world, except in the air and sea. (Biology of Spiders, R.Foelix) These

invertebrates of the order Aranea are one of the several groups of the

Class Arachnida, with about thirty four thousand species. They range in

body size from only a few millimeters in length to almost five inches.

All are carniverous and have four pair of walking legs, one pair of

pedipalps, and one pair of chelicerae. (Spiders, W.Shear) Each

chelicerae consists of a base and a fang. The fang folds up inside of a

groove in the base until needed when attacking food, then moves out to

bite and releases venom from a tiny opening at its end as it penetrates

the prey. (Biology Of Spiders, R.Foelix) They are also used to “chew”,

getting digestive juices inside the body of the prey then squeezing out

the liquid lunch. The pedipalps are mainly used to catch and rotate the

prey while the chelicerae inject it with poison to tear down the tissue.

Later the bases of the pedipalps are used as chewing parts. (The Spider

Book, J.Comstock) But in males, these palps are used to transfer sperm

into the female. These twleve appendages are attached to a dorsal and a

ventral plate, the carapace and sternum which cover the entire prosoma

and provide attachment points.

The bodies of spiders consist of two parts, an anterior part

called the prosoma and a posterior portion called the opisthsoma. These

two portions are held together by a narrow stalk called the pedicel.

This narrow junction allows for the spider to be very limber and acts

somewhat as a hinge between the prosoma and opisthosoma. So as a spider

moves foward creating a web, it can continue in a straight line throwing

its webbing in the direction it chooses. This is how spiders create

their zig-zag web formations. (Biology of Spiders, R.Foelix)

Covering both the prosoma and the opisthosoma is a waxy covering

that enables the spider to be a very efficient water conserver. This is

one of the characteristics that spiders evolved to adapt to the harsh

conditions of terrestrial life. There are eight eyes located in the

head region usually in two rows, varying among families. Spiders that

wait for and lunge at its prey will have a row of very large eyes well

adapted at detecting the precise distance it is from its prey. Yet

those spiders that make webs do not have as great a need for such

advanced sight and have smaller eyes. But not all spiders have eight

eyes. There are some spitting spiders that have only six, and there are

some with only two or four eyes. Some cave spiders have no eyes at all

and rely only on vibration. There are great differences in the ways

which spiders capture prey. Some may stalk their prey, while others may

lie in wait and ambush it. Other spiders may weave various types of

webs used to capture passing prey, and there are some smaller commensal

spiders that live in larger spiders’ webs and feed on the smaller

insects neglected by their host. (The Spider Book, J.Comstock)

All spiders spin silk, though not all of them weave webs. Silk is

most commonly seen used in forming webs, which may vary from a highly

elaborated orb of spiraling threads to a single sticky string. Most

webs can be placed into one of four different types: the orb webs, the

funnel webs, tangle webs, and the sheet webs. The main purpose of a web

is for catching prey. With orb weavers (Araneidae), the spider will

first form a supporting structure of frame threads to which it will then

add on radial threads. (Biology of Spiders, R.Foelix) These tightly

strung threads provide quick access to any where on the web, and also

carry any vibrations from the outer perimeter to the center. (The Spider

Book, J.Comstock) After the innitial threads are placed, the spider

will build on a catching spiral made of sticky silk. These spirals will

be what capture and snare prey until the spider is able to reach it and

inject it with its venom. Orb webs are very delicate and lose their

stickyness after a short period. So many orb weavers take down and

replace their old webs daily. (Spiders, W.Shear) They recycle the old

silk by eating it as they lay out the new silk. Orb weavers must also

consider orientation with respect to where the wind is coming from,

because they will also snag leaves and blowing debris. (The Spider Book,

J.Comstock) When the orb is completed, many orb weavers remain in the

center of the web called the hub. They will wait here for their prey.

When the web is hit by an insect, the spider turns in the hub to face

the direction from where the vibration came. It will then jerk the web

sharply to entangle the victim by rapidly flexing one of its front legs.

(Biology of Spiders, R.Foelix) Eventually after it is sure that the prey

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