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

is stuck in the web, the spider will follow down the strand. Once it is

at a close enough distance to make contact, the spider will rush at and

quickly bite its victim, then retreat away until the venom has taken

affect. After subduing the prey, the spider will wrap it in silk before

or after carrying it back to its hub or the site it may choose to hide.

There are more than 2000 orb weaving species and no two species

build exactly the same web. (The Spider Book, J.Comstock) But in most

cases the differences are very minor and only concern the symmetry of

the web. (Biology of Spiders, R.Foelix) But there are three demensional

orb weavers that add extra threads from the center to an outside

support, thus pulling out the web into a cone shape. This enables the

spider to wait at the new attachment sometimes being the attaching

bridge. When an insect flies into the web area the spider may cut or

simply release the wed so that it goes back and ensnares the flying

victim. (Spiders, W.Shear)

Funnel webs spiders (Agelenidae) are also common spiders. They

can be easily found outdoors in short grasses or small bushes, to large

vegetation, and even between building edges. Their flat web narrows

into a funnel like closure at one end where the spider hides and waits

for victims. This funnel is the spider’s retreat, and is opened at both

ends. With its legs feeling for any vibration, the spider can quickly

ambush any insect that may blunder into its web, darting out and biting

it. (Spiders, W.Shear) The insect will not be eaten where it is

captured, but will be taken back into the spider’s retreat where the

feeding process will actually take place.

Sheet webs do not have any stickyness to them nor is there a fixed

pattern by which they are placed. Instead an insect that may pass by

will become entangled in the vertical strands that act like a tripping

line, connected to the spider’s sheet web underneath. Sheet web spiders

(linyphiids) always hang beneath their dome web, and when there is prey

trapped in the vertical strands, they will shake the web so that it will

fall onto the sheet. The spider will then pull its victim down through

the web while biting and poisoning it.

The tangle web spiders are much like the linyphiids, but their

sheet has a much more loose and irregular pattern. Extending down from

the sheet are vertical strands that are loosely connected to the ground,

and are covered with sticky droplets a few milimeters from the ground.

An insect passing by that touches one will stick to it and break it from

the ground. While trying to pull free it will tangle itself up in more

similar strands while the spider drops down to subdue it. Some of these

spiders build retreats that they cover with dirt and pieces of leaves

that they will hide in and carry prey into to eat. A variation of this

retreat is that of the purse web spider (Atypus). This spider has a

silken retreat that is mostly buried underground but has a baloon like

tube outside that is covered with soil and bits of debris to appear like

normal ground. When an insect walks across or lands on it the spider

will bite it from beneath and pull it through the web.

Spiders do not only use threads to make webs and bound prey. Non

web weavers use silk threads to climb up and down with, as well as for

draglines. These latter threads are used to both help a spider slow

down and to catch it encase it falls as it leaps from one place to the

next, such as from flower to flower. Jumping spiders, most common to

the class Salticidae, are known for using draglines for anchoring and

quick stops. These spiders use their last pair of legs to propell them

from the ground in long or short leaps. Salticids use this jumping

ability not only for catch prey but also to escape danger. These

spiders can jump up to twenty five times their body length, which is

very long for an insect with out any specialized jumping legs. As

mentioned earlier jumping spiders have larger eyes for being able to

distinguish visible objects at greater distances. (Biology of Spiders,

R.Foelix) This makes good since, because they have no other way to

obtain prey but with their own stealth and accuracy. They react very

accutely to any visual stimulus. First they will turn to face the

stimulus and then walk closer towards it. They will stalk their prey

until within at least ten centimeters to be able to completely identify

it then attack. Once the victim is captured, it is usually consumed

right where it is. Their front legs are stronger so that they may seize

prey, and they have strong perpendicular fangs to penetrate and hold

prey firm.

A similar spider to the jumping spiders is the wolf spider. These

spiders lie in ambush and attack their prey. They too have a large set

of eyes on their upper posterior row, above a row of four generally

small eyes. Although wolf spiders have well developed eyes, they react

mainly to vibrations recieved from beating wings or movement from

insects on the ground. As with the jumping spiders, there are a large

pair of fangs that extend down to help assist in seizing prey. The most

well known wolf spider is the tarantula. These spiders can reach up to

ten inches in their complete lengths. And although lore has it that

they are one of the most poisonous spiders, their bites are only painful

to humans, not deadly. (Biology of Spiders, R.Foelix)

Though feeding habits vary with spiders their methods of

reproduction are all relatively similar, though each species has its own

specific ritual. Because spiders are cannabilistic, the much smaller

male must be very cautious in approaching a potential mate. If he

simply rushes in towards the female, the chances are that he will be

seen only as food and consumed. So spider courtship has evolved into a

special complex pattern that varies in each species. This variation

allows for species recognition, so no gametes are was