Spiders
are easily recognized by people because
of their eight legs. Spiders are not
classified as insects for this reason,
as all insects have six legs. Another
difference between spiders and insects
is that spiders have neither antennae
nor wings.
There are many species of spiders common
throughout households in the United
States. Their presence may be known by
the webs they spin before any actual
spiders are spotted. The only spiders
that pose a serious threat to safety in
the U.S. are brown recluse and black
widow spiders. All spiders inject venom
into their prey when they bite, but
brown recluses and black widows are the
only ones that have extremely dangerous
venom for people.
All spiders have the following
anatomical features:
Cephalothorax: The cephalothorax
is one of the spiders' two body regions.
It is a head and thorax fused together
as one.
Abdomen: The abdomen is the
second of the two regions that spiders
have.
Chelicerae: All spiders have a
chelicerae, which is a jaw-like
structure. On the end of each chelicerae
is a hollow, claw-like fang. At the end
of each fang is a small opening through
which venom is injected into prey.
Spinnerets: At the tip of the
spiders' abdomens are spinnerets. They
are silk spinning glands for web-making.
Spiders lay eggs in ball-shaped silken
egg sacs that are either carried by the
females or hidden in webs. In their
lifetime, spiders may produce several
egg sacs and each sac may contain
several hundred eggs. One female may
produce as many as 3,000 eggs in a
series of several sacs over a period of
time.
Eggs usually hatch a few weeks after
being laid or the following spring and
then take a year to develop. A spider
grows through the process of molting,
which is the shedding of skin. It may
molt 4 to 12 times before reaching
maturity. A spider's life is generally
one to two seasons. All spiders produce
venom that is poisonous to their normal
prey-- insects, mites and other small
arthropods. Venom is injected through
their hollow fangs to immobilize prey.
Since spiders can only feed on liquids,
digestive fluids are then either
injected or regurgitated into the prey
to liquefy the body and make it
ingestable.
Spiders produce silk, which is secreted
as a liquid through their spinnerets.
After air contact, the liquid hardens.
Different types and textures of silk may
be used to construct snares or webs, egg
sacs, draglines and ballooning threads.
Some spiders use web snares to trap prey
and all spiders construct a silk sac to
deposit eggs. Some spiderlings (young
spiders) sail through the air using a
technique known as "ballooning." To do
this, spiderlings climb to a high point
and release silk strands until there is
sufficient drag from the wind to support
their weight. Then, they release their
hold and sail away, often for
considerable distances. These ballooning
threads (gossamer) can fill the air on
clear days as spiderlings disperse to
new areas.
Many spiders are associated with
moisture. Some spiders prefer drier and
warmer environments. Moisture-thriving
spiders are commonly found in basements
and crawl spaces. Spiders that prefer
warm temperatures frequent air-vents,
attics, and the upper-corners of rooms.
Regardless of their temperature
preference, they almost always stay in
cracks, darkened areas, or hiding spots
constructed from their silk.
When outdoors, spiders feed
on insects
and are therefor very beneficial.
However, when they are found indoors,
they construct webs to catch prey; when
this happens, they can be an unsightly
nuisance.
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