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Spiders
Identification
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.
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