|
Spiders have
eight legs (four pairs). They have two body regions: a
cephalothorax (fused head and thorax) and an abdomen,
which are joined together by a narrow waist. Most
spiders have six or eight simple eyes in various
arrangements. All have a pair of jaw-like structures,
the chelicerae, each of which ends in a hollow fang
through which venom can be ejected. The tip of the
abdomen has a group of small fingerlike spinnerets that
produce silk. Young spiders (spiderlings) resemble
adults except for their smaller size and coloration.
Web Builders
Many spiders use webbing to ensnare
their prey. Their web designs vary and may or may not be
elaborate. Web-builder spiders discussed here include
cobweb spiders, orb weaver spiders, cellar spiders, and
funnel web spiders.
The web building habits of cobweb
spiders contribute to their pest status. These spiders
typically construct an irregular web in sheltered sites
indoors or outdoors. The outer sticky threads of the web
entangle insect prey. These spiders often are
inconspicuous, although their web is not. Some species
construct a retreat within the web and hide therein
during the day, and the spider hangs upside down in the
center of the web at night.
Cobweb spiders, including widow spiders,
belong to the family Theridiidae and have a rounded
globular abdomen (black widow spider shape). One member
of this family, the common house spider (Achaearanea
tepidariorum) is about 1/3 inch long (female), gray
to brown, and its spherical abdomen has several dark
stripes near the tip. The common house spider requires
high humidity and plentiful prey; it typically occurs in
damp basements, cellars, crawl spaces, and outbuildings.
This species frequently abandons webs that do not yield
prey, and then constructs new ones until it finds a
productive site. Webs become dust covered when
abandoned.
Orb weaver spiders construct the
familiar circular, flat, elaborate web in which flying
insects are trapped. Each species of orb weaver
typically constructs a web with a distinctive design.
Webs usually occur outdoors. These spiders have poor
vision and locate their prey by feeling the vibration
and tension of the threads in their web. They use silk
to wrap the victim.
Many species of orb weaver spiders are
large (approximately 1 inch), but others are quite small
(approximately 0.1 inch). Some have oddly shaped
abdomens (pointed spurs, conical tubercles, etc.). Some
are very brightly colored. One common spider, known as
the yellow garden spider (Argiope aurantia), has
silver hairs on the back of the cephalothorax and a
large abdomen marked in black and bright yellow or
orange. This spider is about 1 inch long and hangs head
down in the center of the web, which is found in
brambles, bushes, tall grasses, etc. in open sunny
places.
Despite their formidable appearance, orb
weaver spiders are not considered dangerous. Some
species can bite if handled.
Cellar spiders are frequently found in
dark, damp places such as cellars, basements,
crawlspaces, and outbuildings. They typically construct
a loose, irregular-shaped web in a dark corner. Cellar
spiders continually add to their web, which can result
in extensive webbing. The male and female live together
in a web and can be found hanging upside down in it.
They shake the web violently when alarmed. Cellar
spiders can quickly establish large populations in a
structure.
Cellar spiders have very long, slender
legs (up to 2 inches long). Their body is about 1/3 inch
long and pale colored (whitish-yellow to gray). They are
sometimes confused with daddy-long-legs (see
HYG-2060B-04).
Funnel web spiders construct large,
flat, horizontal webs of nonsticky silk. The web
contains a funnel at one end that serves as the spider’s
retreat. The funnel is open at both ends so the spider
can readily escape. The spider hides at the narrow end
of the funnel; when it feels the vibration of an insect
crossing the web, it dashes out, bites the insect, then
carries it back to the funnel. In former times, the silk
of funnel web spiders was used to cover wounds to stop
bleeding.
Funnel web spiders generally are brown
and somewhat large (>1/2 inch long). Some species have
banded legs. Some species have long spinnerets that
extend out beneath the rear of the abdomen.
In the family Agelenidae, some species
of Agelenopsis (grass spiders) and nonnative
Tegenaria (house spiders) will infest structures,
but their webs typically are confined to the lower
levels. The hobo spider, Tegenaria agrestis, was
introduced from Europe and is found in parts of the
Pacific Northwest. The hobo spider is known to bite
humans, and its venom has similar effects to that of the
brown recluse spider. Hobo spider bites are probably
from the males, which wander in search of female mates.
The bites of other funnel web spiders are not known to
be very toxic to humans.
Active Hunters
Some spiders actively search for their
prey. Any webs that they construct are used as resting
areas. These spiders are commonly encountered when they
venture from their retreat to search for prey. Spiders
discussed herein that actively hunt include wolf
spiders, jumping spiders, and nursery web spiders.
These hunting spiders are fast runners
that will chase their prey. Wolf spiders are hairy and
often large, up to 1-3/8 inches long, sometimes confused
with tarantulas. Their legs are long and spiny. Many are
dark brown.
Wolf spiders may hunt day and night.
They usually occur outdoors, but may wander indoors in
search of prey. They tend to stay at or near floor
level. They typically construct web retreats in
sheltered sites.
Females carry their large, globular egg
sac attached to spinnerets under the abdomen. Upon
hatching, the spiderlings climb onto their mother’s back
and stay there several days or more before dispersing.
Wolf spiders frequently alarm homeowners
because of their large size and rapid movements. Wolf
spiders are not aggressive, but may bite if handled.
These spiders are so named because of
their jumping ability. They can jump many times their
own length. They make quick, sudden jumps to capture
prey or avoid a threat. They also can walk backward.
These common spiders are about 1/8 – 3/4
inches long, very hairy, stocky built, and short-legged.
Two of their eight eyes are very large. They have the
keenest vision of all spiders. Many species have patches
of brightly colored or iridescent scales. Some are black
with spots of orange or red on the upper surface of the
abdomen, at times confused with black widow spiders.
Jumping spiders are active during the
day and prefer sunshine. They normally live outdoors,
but jumping spiders can become established indoors and
their hunting activities often center about windows and
entry doors where their prey is most common.
These spiders attract much attention due
to their large size as they can have a leg span of 3
inches. Many are earth tone colored.
Nursery web spiders typically live near
lakes and streams, but occasionally are found indoors in
moist areas. Many can run over the surface of water and,
if chased, dive and stay submerged for some time. They
hunt day and night for aquatic insects and even small
fish. They are sometimes commonly called fishing
spiders.
The sole use of their silk webbing is
for the egg sac. The female uses her mouthparts to carry
the egg sac under her body until the spiderlings are
ready to emerge. She then fastens the egg sac to some
leaves and encloses it within a “nursery” web, where the
spiderlings remain until they are ready to disperse. The
female stands guard near the nursery web to protect her
young.
Passive Hunters
Passive hunters are spiders that lay in
wait for their prey rather than searching for it. When
their prey approaches, they may jump or pounce to seize
it. Crab spiders are the only passive hunters discussed
here, although tarantulas and many other spiders employ
this technique to obtain food.
These spiders have a flattened body and
hold their legs at right angles to their sides,
presenting a crablike appearance. They can walk forward,
backward, or sideways.
Many crab spiders have horns or
ornaments on the cephalothorax or abdomen, and some
mimic bird droppings. Those that inhabit trees or hunt
on the ground are usually colored with shades of gray,
brown, or black, while those that frequent flowers are
bright red, yellow, orange, white, and/or green.
Spider Relatives
The class Arachnida includes spiders and
some other arthropods that are closely related to them.
Close relatives of spiders are found in 10 orders and
include scorpions, pseudoscorpions, mites, ticks, and
daddy-long-legs (also called harvestmen).
Daddy-long-legs are very commonly confused with spiders
due to their general appearance and eight legs, but
these tan to brown creatures belong to the order
Opiliones and are not spiders.
|
.jpg){kind=small}
.jpg){kind=small}
.jpg){kind=small}