Spiders

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