What is a Spider?
Spiders are different from insects, but they have
many things in common. They do not have backbones, they are invertebrate
animals, they have jointed legs, and they have exoskeletons. Spiders
are arthropods. They have legs with many joints and a hard outer
body covering called an exoskeleton. Spiders form the second largest
group of arthropods with insects making up the largest group.
How do you tell a spider from an insect?
Spiders have 4 pairs of legs, and two body segments.
They do not have wings or antennae. Spiders belong to the class
Arachnida while insects belong to the class Insecta. There are other
beside spiders that make up the class Arachnida. Scorpions, ticks,
mites and harvestmen belong to the Arachnida class.
There are more than 37,000 species of spiders that
have been identified. Scientists believe that there are as many
species not yet discovered. There are about 3000 species of spiders
found in North America and approximately 700 species found in Florida.
Spiders vary in size from the 10 bird-eating
tarantulas of the rain forest to as small as the point on a safety
pin. They are found everywhere on earth.
The spiders body has two main parts, a combined
head and chest called the cephalothorax. This is where the eyes,
mouth, fangs, jaws and pedipalps are located. The 4 pairs of legs
are also attached to the cephalothorax. The second part of the body
is called the abdomen. The spinnerets are located at the end of
the abdomen. The word spider means maker of silk and all spiders
make silk. The silk is made in the abdomen and is squirted out the
spinnerets. Silk is liquid until it hits the air and then hardens
into strands of silken line.
Spiders are carnivores, they eat other animals.
A spider bites its prey with the fang at the tip of the jaw. The
jaws are called chelicerae. The venom is injected into the prey,
paralyzing or killing it. The spider may use its pedipalps or feelers
to sense what is around it and to hold its prey down while it bites
with its fangs. The venom and digestive juices dissolve and liquify
the prey. The spider then sucks up the liquid using its stomachs
pumping action. Spiders can only eat liquid food, so the chelicerae
strain the liquid. The exoskeleton of prey is discarded after the
Spiders have six spinnerets that make up to seven
different kinds of silk: thin strands, thick strands, sticky strands,
smooth strands or combinations. Silk is made up of a protein fiber
which is the strongest natural made substance in the world. Spiders
use silk in many ways: for safety lines, draglines, for signal lines,
for webs, for egg cases, for holding prey, for building nurseries,
for transportation, as in ballooning, and for snaring prey.
Spiders are divided into 2 general groups, web
builders and non-web building spiders. All spiders make silk, but
all do not make webs. They can be divided into wandering spiders
who search out prey, or waiting spiders, who sit and wait for prey
to come close to them and then they ambush the prey and water spiders,
who trap a bubble of air under their abdomen and take their air-chamber
below the water and get their prey.
Web-weaving spiders build webs to catch prey and
they live in or near the web. The web-builders are arranged by the
shape of their web. The orb weavers design circle webs, the sheet
web spiders form flat horizontal webs, funnel webs are cone-shaped
webs, dome shaped webs are upside down bowl shaped, and tangle webs
are irregular and haphazard in appearance. In some webs the spider
has a personal resting spot which may be obvious, or it may be hidden
in or near the web. It is usually the female spider that is observed
in a web. The male spider only makes a web when he is very young.
At maturity he leaves his web and searches for a female.
Spiders lay many egg cases which they construct
with their silk. Some spiders place these eggs in a well hidden
location and some spiders carry the egg case with them until it
hatches or is close to hatching and then the female constructs a
nursery web for the young spiderlings. Baby spiders are called spiderlings.
They remain in and around the egg case until they have molted and
then they balloon away.
Ballooning helps spiders to avoid over-crowding
and competition for food. Spiderlings climb to the highest point
they can find. They tilt their abdomen and spinnerets upward as
they release silk. The strand of silk lengthens and is picked up
by the breeze and the spiderlings are pulled upward and travel to
a new location. They manage to find the appropriate environment
for their survival, in buildings, shrubs, forests, leaf litter and
lawns. Many spiders only live for one or two years, but some kinds
of tarantulas live for 20 years.
While all spiders in the United States are poisonous,
most spiders are not dangerous because they cannot harm people.
Their fangs are not strong enough to break the skin or their venom
is too weak to affect us. There are some spiders which could be
dangerous. These are the sac spiders because their venom is strong
and some people have an allergy to it. Sac spiders wrap themselves
up in a sac-like tubular resting site inside a rolled leaf. The
widow spiders are comb-footed spiders. In Florida are Black, Brown
and Red Widow spiders. The most dangerous of these is the Black
widow spider. The female black widow spider is less than 1/2 inch
long, has a round, spherical, shiny black abdomen. A bright red
hourglass pattern is on the underside of the abdomen. Black widow
spiders are secretive and hide in their irregular tangle webs built
in dark places or under fallen branches. The brown recluse spider
is called the "violin" spider because of the pattern of
a violin on its cephalothorax. Her venom is harmful to humans. The
brown recluse spider is about 1/2 inch long, brown with the violin
pattern on her back. The brown recluse is shy and secretive. It
hides in a loose web built under furniture, or in dark places. This
spider may hide in closets or in folded clothes which are not used
often. These spiders, the widows and the recluse spider, rarely
Spiders are very helpful. They control many insects
by preying on them. They are the most important predator of insects
in the world. As you learn more about spiders you may become fascinated
with them. As you become fascinated you may become less fearful
of them. Follow safety rules when watching them and remember that
spiders go out of their way to stay out of peoples way.