|
Order: Araneae
|
|
Common Name--Spiders
|
|
Names
|
The class Arachnida, pronounced "a-RACH-ni-da" includes the
orders for spiders, mites, scorpions, and other arthropods with
eight legs. The order Araneae is pronounced "ah-RAY-ne-ah".
Araneae is the Latin word for spider.
|
There are many different names for the species of spiders in
the world. Some of the more recognizable names are black widow,
brown recluse, trap-door spider, tarantula, fishing spider,
crab spider, and jumping spider.
|
|
Diversity
|
More than 35,000 spider species occur in the world. Of these,
about 3,400 species in 64 families are found in North America.
Almost one-fourth of the species in North America are dwarf
spiders and sheet web weavers (family Linyphiidae). Other
large families include the jumping spiders, cobweb weavers,
wolf spiders, and orb weavers.
|
There can be great numbers of spiders within a small area. In
one study, one acre in a grassy field was found to have
2,200,000 spiders.
|
|
Habitats
|
Spiders are mostly terrestrial (land dwelling), but some are
aquatic and spend most of their time in or near water. Some
spiders live in bushes and trees, and others live in tall
grass or on low-growing plants. There are those that live
under stones, logs, and bark. There are spiders that live in
holes in the ground, in caves, in houses, and even on top of
mountains. In fact, jumping spiders have been collected on Mt.
Everest at a height of 22,000 feet (the highest elevation any
animal has been collected).
|
|
Form and Function
|
Adult spiders range in length from less than three hundredths
of an inch to more than 10 inches (counting leg span). They
can be somewhat smooth or very hairy in appearance. Many
spiders are dark colored with different shades of brown being
common. There are also many very bright and beautifully
colored spiders, especially in tropical regions.
|
Spiders differ from insects in several ways. Spiders have two
main body regions: the cephalothorax (the head and thorax areas
fused together) and the abdomen. Insects have three body
regions: head, thorax, and abdomen. The cephalothorax of a
spider has hardened areas on its top and bottom, whereas the
abdomen is very soft. The cephalothorax and abdomen are
connected by a slender waist. Other arachnids, like mites and
scorpions, differ from spiders in having the cephalothorax
broadly joined to the abdomen.
|
Spiders have simple eyes; insects have both simple eyes and
compound eyes. Spiders usually have eight eyes, but they may
have six, four, two, or none. Unlike insects, spiders do not
have antennae.
|
Spiders have eight legs, whereas insects have six. Each
spider leg has seven segments: coxa, trochanter, femur,
patella, tibia, metatarsus, and tarsus with attached claws.
Insects do not have a patella between the femur and tibia.
Spiders that spin webs usually have three claws, which they
use to handle the silk threads. Hunting spiders that do not
spin webs have only two claws.
|
Spiders have two pairs of mouthparts, the chelicerae and the
pedipalps. Each chelicera has two segments. The first
segment is large and sometimes works like a jaw in crushing
prey. The second segment is fang-like and has a small opening
near its end for injecting venom into the prey.
|
The pedipalps appear to be shorter legs in front of the spider.
The base of the pedipalp also is used to crush food. The
tips of the pedipalps of males are swollen and modified for
transmitting sperm during reproduction.
|
The book lungs are the main breathing organs of spiders.
These organs are located inside the front end of the abdomen.
The openings of the book lungs are on the underside of the
abdomen at the edges of a groove. The inside of each book
lung has several sheetlike leaves (like the pages of a book)
that obtain oxygen from the air. In addition to book lungs,
a single spiracle is present at the tail end of the spider,
and this is connected to the trachea.
|
Some spiders disguise themselves as insects or other natural
objects. They can be long and slender and resemble pieces of
straw or grass. There are also many spiders that resemble
assassin bugs and ants. Some spiders resemble bird droppings.
|
Spiders can make different types of silk with glands and
spinnerets at the end of the abdomen. Some silk, such as that
for catching prey, is sticky, but other silk is not, such as
that used for making an egg case. Spider silk is very strong,
and in fact, the strongest natural fiber known is the silk of
spiders in the genus Nephila.
|
|
Life Cycle
|
Female spiders lay their eggs in silken cases, or sacs. These
sacs are placed in many different places--on leaves, in cracks
of bark, or on a web. Some spiders, such as jumping spiders
and crab spiders, guard the egg sac until the spiders hatch.
Sometimes the egg sacs are carried by the mother until they
hatch. Some spiders, such as wolf spiders (family Lycosidae),
carry their young spiderlings on their backs after the young
hatch.
|
Spiders have simple development with little metamorphosis. The
young spider, or spiderling, resembles a small adult when it
hatches. It molts between four and twelve times before
reaching maturity. Some species continue to molt throughout
their adult lives.
|
Mating of spiders can involve very elaborate courtships prior
to the actual mating act. Some males give the females a fly
or other food before mating. Some male spiders, such as the
wolf spiders, perform dances while waving their legs at the
potential mate. They also can make sound by stridulating or
drumming the ground with their mouthparts during their
courtship.
|
The female of a few species may kill and feast on her mate
after mating, but this is not common. The black widow is one
spider that is well-known for doing this. Some male and
female spiders live together in the same web.
|
Most spiders live only a year or two. Other spiders, including
the brown recluse, can live between five and ten years.
Tarantula spiders require several years to mature. The males
only live a year or so after maturing, but the females live
longer. Some species of tarantulas have lived 28 years.
|
|
Form and Feeding Habits
|
All spiders are carnivorous in their eating habits, and insects
are the primary prey. Spiders usually catch live animals
because the movement of the prey attracts the spider's
attention. Some spiders have poor vision, and they depend on
movement of the web to know an insect prey has been caught.
The prey usually is wrapped in silk before the spider injects
the venom to kill it.
|
Some spiders have been known to capture and kill vertebrate
animals. Fishing spiders in the genus Dolemedes sometimes
capture small fish. The large bird spiders of South America
have been known to catch small birds as well as lizards.
Spiders even have been known to attack and feed on snakes.
The spider does not kill the snake immediately, but instead
wraps the snake's mouth and body with silk webbing. The
snake then is pulled up into the web where the spider feeds on
it for several days.
|
Spiders have great appetites, and their abdomens can swell to
hold large amounts of food. Prey may not be available always,
and some spiders can go for several weeks without eating.
|
Many spiders use different kinds of webs to trap their prey.
The web made by orb-weaver spiders (family Araneidae) is one
of the most familiar kinds of webs. The orb weaver makes a
frame and straight spokes extending from the center, rather
like those of a bicycle wheel. The spider starts a spiral of
silk at the center of the wheel and goes around and around
until it reaches the edge. The spider then retraces its
spiral back to the center of the orb web.
|
Some spiders build sheet webs, such as those on a grassy field
that are rather flat and facing the ground. The bowl and
doily spider rests on the underside of the curved bowl-shaped
part of the web and is protected from predators by a sheet-like
"doily" of silk below the bowl.
|
Many spiders build cobwebs, which are masses of web that are
irregular or without a distinct form. Cobwebs are found
often in corners of rooms of people's houses. Some spiders
build funnel webs, which are thick and funnel-shaped. Some
spiders live in the webs of other spiders and eat insects
missed by the spider that made the web.
|
Trapdoor spiders dig a tunnel in the ground in which to live
and ambush their prey. The spider lines the tunnel and
opening with thick silk. The spider then cuts around most of
the rim of the opening, forming a hinge so the door can open
and close. The door is camouflaged so that it is not visible
from above. When an insect walks across the surface of the
door, the spider rushes out and captures its victim. Trapdoor
spiders can hold their doors shut tightly to prevent predators
from entering.
|
Other spiders that ambush prey include the crab spiders and
some lynx spiders. These spiders are often camouflaged so they
blend into the background where they wait for prey. Some crab
spiders can change their color to match the flower where they
are sitting. A crab spider will have a yellow body on a yellow
flower, but it can become a white spider on a white flower.
|
Wolf spiders (family Lycosidae) and jumping spiders (family
Salticidae) are active hunters for their food. Most wolf
spiders live on the ground, and many dig burrows in which to
hide. Their large eyes glow at night like miniature stars on
the ground when a flashlight shines on them. Jumping spiders
can be found on the ground or on plants. Both wolf spiders
and jumping spiders jump on their prey to kill it.
|
|
Natural Enemies
|
Spiders can be their own enemies. Many young spiders do not
hatch or live long because they are eaten by their brothers or
sisters, a habit known as cannibalism. Enemies of spiders
include birds, reptiles, mice and other small mammals, and
certain insects. Mud dauber wasps and other sphecids use
spiders as a source of prey. The wasp family Pompilidae,
commonly known as spider wasps, prey only on spiders, and some
will attack large tarantulas. Parasites of spiders include
ichneumon wasps and some flies. Some mantidflies in the order
Neuroptera feed on spider eggs.
|
|
Olympic Feats and Other Strange Facts
|
Some tropical orb weavers in the genus Nephila spin webs that
are more than eighteen feet across. These webs are so strong
that they can catch small birds and bats in addition to insects.
People have used their webs as nets to catch fish.
|
The giant bird-eating spider, Theraphosa blondi, of
South America is the largest spider in the world. This spider
may have a leg span of 10.5 inches, a body length of 3.5
inches, and can weigh up to 4.3 ounces.
|
The smallest spider in the world is the Samoan moss spider,
Patu marplesi, which has a leg span of only 0.017
inches.
|
Greek mythology includes the story of the origin of spiders.
There was a lady named Arachne who was a weaver of beautiful
patterns. Arachne challenged the goddess Athene to a weaving
contest, and Arachne won. Athene was angry to lose the
contest, and she tore up Arachne's weaving. Arachne was so
upset and sad that she killed herself. The goddess Athene was
very sorry about what had happened, and so she turned Arachne
into a spider so that her beautiful weaving would not be lost
to the world.
|
Jumping spiders can pounce on their prey from a distance of
forty times their own body length.
|
Tarantulas defend themselves, not with their fangs, but with
hairs on their body. The spider can flick off the hairs with
its legs if it is threatened, and these hairs can irritate the
skin, especially the nose and eyes.
|
Spiders can sometimes regenerate their legs if they are lost.
|
An equal volume of the venom of the black widow spider,
Lactrodectus mactans, is 15 times more toxic than
rattlesnake venom.
|
Web spinning spiders usually spin a new web every day. A web
with 1,000 individual attachments of the silk lines can take a
spider less than a half hour to complete.
|
In 1922 Professor W. J. Baerg, at the University of Arkansas,
tested the effect of a tarantula bite on himself. He had
difficulty in getting the tarantula to bite him. When it
finally did bite him, the slight pain did not last long, and
the venom was not poisonous. The next year he tested the bite
of the black widow on himself, recording the progress of the
venom as it affected his body. Nine hours after being bitten,
he went to the hospital where he stayed for the next three days.
|
Young spiderlings move to new locations by "ballooning."
The spider spins a silk line that is caught by the wind,
carrying the spider with it. Ballooning spiders have been
captured at 5,000 feet above ground.
|
Spider silk is the strongest natural fiber known to man.
Although it may be only one millionth of an inch thick, it can
stretch more than a rubber band.
|
American Indians once used the mashed bodies of black widow
spiders as an arrow poison.
|
The diving bell spider, Argyroneta aquatica, lives most
of its life underwater. The spider, which occurs in Europe and
Asia, lives in bell-shaped homes that are made with a silken
sheet tied to water plants. Diving bell spiders bring air from
the surface of the water to fill their homes under the water.
|
|
The Good and The Bad
|
Spiders have provided benefits to humans and are an important
part of the ecosystem. Some species are beneficial predators
of pests in crops. But, they also prey on insects that are
beneficial, such as the honey bee. Spider silk has been used
for the cross hairs in gun sights and other instruments.
In the early 1700's, spider silk was used by a man in France
to make fine gloves and stockings. The cannibalistic habits
of spiders prevents them from being raised together to make
silk production practical.
|
Spiders hold a special place in literature and art. Many
stories and poems have been written about spiders. Tarantula
spiders have been used to create fear and danger in many
television shows and movies, even though these spiders are
relatively harmless.
|
The only spiders that are dangerous to people in the United
States are several species of the genera Lactrodectus and
Loxosceles. Lactrodectus mactans, the black widow, and
Loxosceles reclusa, the brown recluse spider, are two
of the more well-known species.
|
The black widow spider is easily identified by its shining
black color and a red marking, usually hour-glass shaped, on
the bottom of its abdomen. The black widow can be found
under logs, in junk piles, barns, basements, and similar
places. The black widow venom affects a person's nervous
system, but it usually is not fatal if medical treatment is
obtained.
|
The brown recluse spider has a distinctive dark brown
fiddle-shaped mark on the top of its cephalothorax. Sometimes
it is called the fiddleback spider. It also has only six eyes
(in three pairs), rather than the eight eyes present in most
spiders. The brown recluse is a secretive spider, preferring
dark, quiet places where it won't be disturbed. The venom of
the brown recluse affects the flesh in the area of the bite,
causing the skin and tissue to die and often leaving a scar.
However, people rarely have died from bites of the brown
recluse spider.
|
|
Taxonomy
|
|
Selected Families of North American Spiders
|
Ctenizidae (trap-door spiders)
Theraphosidae (tarantulas)
Atypidae (purse-web spiders)
Uloboridae (uloborid spiders)
Dictynidae (hackled-band weavers)
Loxoscelidae (recluse spiders)
Gnaphosidae (hunting spiders)
Pholcidae (long-legged or cellar spiders)
Theridiidae (comb-footed spiders)
Linyphiidae (sheet-web spiders)
Mimetidae (spider-hunting spiders)
Araneidae (orb weavers)
Tetragnathidae (long-jawed orb weavers)
Thomisidae (crab spiders)
Ctenidae (wandering spiders)
Clubionidae (two-clawed hunting spiders or sac spiders
Agelenidae (grass or funnel-web spiders)
Hahniidae (hahniid sheet-web spiders)
Pisauridae (nursery-web and fishing spiders)
|
|
Selected References
|
Kaston, B.J. How to Know the Spiders. Dubuque, Iowa:
William C. Brown, Co. Publishers, 1953.
Levi, H.W. and Levi, L. R. Spiders and Their Kin.
New York: Golden Press, 1968.
Borror, D.J., Triplehorn, C. A. and Johnson, N. F.
An Introduction to the Study of Insects. Sauders
College Publishing, 1989.
|
|
Links
|
For an extensive list of Araneae Web sites, go to the Links Component of the module.
|
|
Picture Credits
|
Dr. Ross E. Hutchins (Deceased)
Mississippi Entomological Museum
An orb weaving garden spider
Gasteracantha spider on web
Fangs of chelicerae with venom
A jumping spider, not an ant
Black widow with egg case
Wolf spider carrying spiderlings
Spider building orb web
Bowl and doily spider
Trapdoor spider lifting door
Crab spider on goldenrod
Wolf spider
Nephila spider
Spiderling ballooning with silk line
Green lynx spider with ladybird beetle
Bottom of abdomen of black widow spider
Brown recluse spider
|
