Argiope aurantia
Garden spider
Systematics
P
Arthropoda , Chelicerata sP, Euchelicerata, Arachnida C, Araneae O,
Aranaeomorphae sO, Neocribellitae iO, Araneidae F
Chelicerata sP
Chelicerata is a large taxon that includes spiders, scorpions, pseudoscorpions,
ticks, mites, horseshoe crabs, sea spiders, and many others. The group originated in
marine habitats but almost all modern chelicerates are terrestrial.
The body is divided into an anterior cephalothorax with six pairs of appendages
and a posterior abdomen which, in most groups, does not bear appendages or has
highly modified appendages. The first appendages of the cephalothorax are the
chelicerae. Antennae are not present and the brain has two regions rather than the
three found in mandibulates. Appendages are primitively biramous but are uniramous
in almost all Recent taxa.
Euchelicerata
The segments of the cephalothorax are fused and covered by a dorsal shield, or
carapace. Two median eyes are present.
Arachnida C
Arachnids are the terrestrial descendents of the early aquatic chelicerates. The
taxon includes the mites, scorpions, pseudoscorpions, spiders, harvestmen, and several
other taxa. All are adapted for a terrestrial existence with internal gas exchange and a
waterproof integument. Some are capable of silk production and many use toxins to
subdue or kill the prey. Most are carnivores, digestion is usually outside the body, and
food is liquefied before ingestion.
Araneae O
Spiders are arachnids with unsegmented cephalothorax and abdomen (in
most). The cephalothorax bears six pairs of jointed segmental appendages whereas
the abdomen bears none, although it has structures derived from them. The
anteriormost appendages are chelicerae used to inject poison into the prey. Respiration
is via book lungs and/or trachea and excretion is via Malpighian tubules and saccate
nephridia known as coxal glands. The heart is a dorsal tube in the
abdomen. Abdominal silk glands spin silk for many purposes including the construction
of a web for prey capture. All spiders are carnivores that capture living prey. Poison is
used to subdue the prey, which is then digested externally by enzymes from the gut,
usually following thorough external mastication. The nervous system is highly
cephalized and consists of a large nerve ring in the middle of the cephalothorax from
which nerves arise. Spiders are gonochoric and sexually dimorphic. Fertilization is
internal but sperm transfer is indirect and spermatophores are not used. Males are
usually smaller than females.
Aranaeomorphae sO,
Araneomorphae is by far the largest spider taxon with 90 families and over
30,000 recent species. The fangs are either diagonal or labidognath, not
orthognath. The abdomen is not segmented. Most taxa have one pair of book lungs
Neocribellatae Io
These are the spiders sometimes known as labidognaths in recognition of their
labidognath fangs that move at right angles to the long axis of the body. There may be
one or no pairs of book lungs. One pair of tracheae is present. Females usually have
an epigynum.
Laboratory Specimens
This exercise is written for preserved female garden spiders, Argiope aurantia ,
but can be used for most other members of the large family Araneidae. The araneids
are orb weavers that build the quintessential, flat, circular spider web. Argiope aurantia,
the North American garden spider, is a common, large, distinctively colored (black and
yellow) species often seen in the autumn in suburban and rural yards, roadsides, and
gardens. Females of this species include a conspicuous zig-zag band of white silk in
the center of the orb and because of this are known colloquially as "writing"
spiders. The male is a small inconspicuous animal but a careful observer can
sometimes find one in its diminutive, imperfect web near the female's much larger web.
Argiope is the genus usually supplied by supply companies but identification is
not always accurate. Males are not usually included in commercially supplied jars of
preserved spiders. Jars of preserved "garden" spiders from commercial suppliers are
likely to include other species in addition to, or instead of Argiope aurantia. Argiope
trifasciata, the banded garden spider, is similar to A. aurantia and almost
indistinguishable from it morphologically. Nephila clavipes, is a large species that
builds gigantic webs in forests across the southern portion of the North American
continent. It has an elongate, angular abdomen and long legs with distinctive tufts of
black setae on some of the articles. Species of Araneus have fat, almost spherical,
abdomens. All belong to the family Araneidae and are similar. Excellent photographs
of Argiope bruennichi can be found
at www.xs4all.nl/~ednieuw/Spiders/spidhome.htm
External anatomy should be studied with the animal moist but in air, whereas the
animal should be immersed in water for dissection and study of internal anatomy. A
dissecting microscope or hand lens should be employed for the study of external
anatomy and a dissecting microscope for internal anatomy. If living specimens are
used they may be anesthetized or killed, as desired, in a jar containing a wad of cotton
dampened with chloroform or ethyl acetate respectively. Preserved specimens used
for external anatomy can be saved and, with care, used for many years.
External Anatomy
Tagmata
Examine a female Argiope, or similar species, using magnification as needed
(Fig 1, 2, 18-18). If the specimen is preserved, handle it carefully as it will be brittle.
The body is covered by an exoskeleton, or cuticle. Some regions of the cuticle
are hardened, or sclerotized, whereas others are soft and flexible but, in general, the
exoskeleton tends to be softer than that of most insects and crustaceans.
Figure 1. Dorsal view of a female garden spider, Argiope aurantia.
Spider48L.gif
Verification_________
The body is composed of two tagmata; the anterior cephalothorax, or prosoma, and
the posterior abdomen, or opisthosoma (Fig 1). The two are connected by a narrow
waist, orpedicel (Figs 2, 5). The bulbous ovoid abdomen is much larger than the
cephalothorax.
Cephalothorax
The cephalothorax consists of the fused head and thorax of the proarachnid
ancestors. It is flattened dorsally and covered by a broad, flat, sclerotized, exoskeletal
plate known as the carapace (Fig 1). A pair of oblique cephalic grooves on the
carapace marks the line of fusion of the ancestral head and thorax. The head is
anterior to the cephalic grooves and the thorax posterior to them. The carapace is
covered by a pelt of fine setae visible only with magnification.
The anterior end of the cephalothorax bears four pairs of large eyes, some of
which are elevated on small tubercles (Fig 3). Each possesses a single large,
transparent lens bulging above the carapace surface. The anterior median eyes, or
main eyes, are homologous to simple ocelli of other arthropods. They are anterior
most and face forward (Fig 4, 18-27). The remaining three pairs are secondary eyes
derived from compound eyes of chelicerate ancestors and include, from anterior to
posterior, the anterior lateral eyes, posterior lateral eyes, and posterior median
eyes. The eyes point in different directions and are simple, rather than compound.
Figure 2. Ventral view of a female garden spider, Argiope
aurantia. Spider49L.gif
Verification_________
Hold the specimen so you can view the anterior end with the dissecting
microscope. The anterior end of the cephalothorax, or face, of the spider is composed
of the anterior carapace and the broad basal articles of the chelicerae (Fig 3, 18-27A).
The chelicerae are the first appendages of the cephalothorax and are
composed of two articles. The proximal article is the large basal piece attached to the
anterior end of the cephalothorax under the edge of the carapace. It contains powerful
muscles and a duct from a poison gland in the cephalothorax.
The second, or distal, article of the chelicera is a slender, sharp, hollow fang at
whose tip the poison duct opens. Spider venom is a mixture of neurotoxins and
proteolytic enzymes. Almost all spiders have poison glands but few are harmful to
humans.
The second cephalothoracic appendages are the pedipalps (Figs 3, 1,
2). These long, slender, leglike appendages are composed of six articles. The
enlarged proximal article, orcoxa, attaches to the ventral side of the anterior thorax
immediately posterior to the fangs (Fig 2). The median process of the coxa is a setose
plate known as the pedipalpal endite, or gnathobase, that masticates food and mixes it
with digestive enzymes (Fig 2, 18-18B). Distally the pedipalps are sensory whereas
proximally they are used to manipulate food. Those of males are modified to transfer
sperm to the female.
The remaining cephalothoracic appendages are four pairs of similar walking
legs (Figs 1, 2). Each is composed of a linear series of seven articles named, in order
from proximal to distal; coxa, trochanter, femur, patella, tibia, metatarsus,
and tarsus (Fig 1). The distal tip of each tarsus bears tiny claws.
Figure 3. En face view of a female garden spider, Argiope
aurantia. Spider50L.gif
Verification_________
The legs have abundant setae, most or all of which are sensory receptors, chiefly
mechanoreceptors sensitive to vibrations, touch, and air movements. Slit sense organs
sensitive to strain in the cuticle are present at various places on the body, especially on
the legs. Trichobothria, which are special, long, slender setae, are sensitive to very
weak air movements. Chemoreceptors are present on the tarsi, especially those of the
first legs.
Most of the ventral surface of the cephalothorax is protected by a large, heavily
sclerotized sternum formed by the fusion of four embryonic sternites (Fig 2, 1818B). Anterior to the sternum is a small triangular labium which extends anteriorly
between the bases of the pedipalpal coxae. The labium is movable along its
articulation with the sternum. It is the sternite of the pedipalpal segment.
The chelicerae, pedipalpal coxae, and labium surround the mouth and enclose
the preoral cavity that precedes the mouth. Within the preoral cavity is a prominent
conical labrumlocated on the midline. Push the chelicerae and pedipalpal coxae aside
to reveal the labrum. The mouth is a triangular opening on the posterior surface of the
labrum and is covered and closed by the labium. It can be seen by moving the labium
posteriorly on its hinge. The heavy fringes of setae on the pedipalpal coxae and labium
filter the slurry resulting from external predigestion before it enters the mouth. Large
particles are excluded and only liquid and very small particles enter the mouth.
Figure 4. Enlarged en face view showing the four pairs of eyes. Spider137L.gif
Verification_________
Laterally the dorsal carapace and ventral sternum are joined by the pleural region
(pleuron) of the exoskeleton. The pleuron is the soft, flexible and unsclerotized area
surrounding the coxae. Little of it is visible because most of it is covered by the coxae of
the walking legs.
Abdomen
The abdomen of Argiope is connected to the cephalothorax by a short
slender pedicel (Figs 2, 5, 18-20), which is visible ventrally. Because the
cephalothorax overhangs the anterior abdomen the pedicel is not visible from
above. The pedicel originates on the cephalothorax between the coxae of the fourth
pair of walking legs and attaches to the anterior end of the abdomen (Fig 2). Dorsally,
the abdomen is featureless except for its striking yellow and black pigmentation (in
life).
A pair of large, pale areas of wrinkled exoskeleton on the anterior ventral
abdomen marks the position of the internal book lungs (Fig 2). The lungs are
invaginations of the exoskeleton elaborated to form numerous tiny lamellae that
resemble the pages of a book (Fig 18-6).
The external openings of the book lungs are oblique slits, known as lung
spiracles (= pulmonary spiracles), just posterior to the lungs themselves. Insert a
microneedle into one of these spiracles to demonstrate its presence.

If instructed to do so, use a pair of fine forceps to peel the exoskeleton off the
surface of the lungs to reveal the lamellae. The lamellae expand the surface area for
gas exchange.
The female epigynum is a large exoskeletal protuberance lying on the midline
between the two lung spiracles (Figs 2, 5). It covers the female gonopores (Fig 5, 1829).
Near the posterior end of the abdomen, but still on its ventral surface, there is a
large circular depression containing several structures. A third spiracle, this one the
median unpaired tracheal spiracle, is the opening into the tracheal system. It lies on
the anterior border of this depression. The tracheae are derived from a second pair of
book lungs which were present in the ancestral spiders.
Also within the depression are three pairs of spinnerets that spin silk (Figs 2, 5,
18-21). The anterior spinnerets and posterior spinnerets are large and easily seen
(with magnification) but the median spinnerets are small and hidden by the other
two. They can be seen by pushing the anterior and posterior pairs aside and looking
between their bases. The spinnerets are derived from abdominal appendages of the
ancestor. The spinnerets are connected by ducts to silk glands in the abdomen (Fig 5,
18-20).
The anus is located subterminally on the posterior surface of the anal papilla.
The papilla is on the midline at the posterior edge of the depression (Fig 2).
Internal Anatomy
Preserved spiders are inferior to fresh specimens for the study of internal
anatomy but a superficial examination of most of the major organ systems can be
accomplished fairly easily, even with preserve material.

Open the animal by cutting it in half along the median sagittal plane. Use a
sawing motion by a sharp scalpel or razor blade for this. Make every effort to keep the
blade on the median sagittal plane so you produce right and left mirror images. You
will find the cut surfaces of both sides to be useful for study. Pin them side by side
under water in a small (anchovy can) wax-bottom dissecting pan so the cut surfaces
face up and are easily examined with the dissecting microscope. The appearances of
structures viewed in these sections will vary, sometimes markedly, depending on the
position of your section. Do not expect your sections to look exactly like Figure 5 or like
each other, or like your neighbor's.
Structures in the abdomen may be more difficult to identify that those of the
cephalothorax. There is very little hemocoelic space in the abdomen and most of it is
packed with digestive ceca or silk glands.
Figure 5. Sagittal section of a preserved female garden spider,Argiope
aurantia. spider51L.gif
Cephalothorax
Look at the cephalothorax and relocate the external structures in the vicinity of
the mouth. You will now have new views of these "mouthparts". Find the mouth on
the posterior surface of the labrum and note, once again that it is preceded by a preoral
cavity bordered by the chelicerae, pedipalpal coxae, and labium. It is closed posteriorly
by the labium.
There is an elongate, hollow poison gland on either side of the midline in the
anterior, dorsal cephalothorax (Fig 5, 18-20). The two poison glands are separated by
a vertical, partition-like sheet of muscle (the pharynx dilator or levator) lying on the
midline. You will probably be able to see the poison gland on one side but not the
other (unless you remove this muscle). The anterior end of the poison gland extends
into the base of the chelicera and empties by a duct leading to the tip of the fang. The
poison glands are muscular and the poison is ejected by contractions of the muscles.
Digestive System
The pharynx is a long, narrow, almost vertical tube extending dorsally from the
mouth (Fig 5, 18-20). The pharynx dilator muscle extends from the pharynx to the
midline of the carapace. Contractions of this muscle dilate the pharynx and draw liquid
food in through the mouth from the preoral cavity.
A slender esophagus extends posteriorly from the dorsal end of the pharynx
(Fig 5). In about the middle of the cephalothorax it widens to form the stomach. The
pharynx, esophagus, and stomach are all part of the foregut and as such are derived
from ectoderm and lined with exoskeleton.
The stomach dilator muscle extends from the dorsal wall of the stomach to the
midline of the carapace. Its action is similar to that of the pharynx dilator. Together the
stomach and pharynx suck food into the gut.
A narrow intestine, or midgut, exits the posterior end of the stomach and
passes through the pedicel to the abdomen. The midgut is endodermal and has no
cuticular lining. A one-way valve prevents the reverse flow of food out of the midgut
when the stomach dilates.
Tubular anterior digestive ceca arise from each side of the anterior end of the
intestine in the cephalothorax. These twisting, cylindrical glands ramify through the
interior of the cephalothorax but lie out of the plane of section and may be difficult to
discern.
In the abdomen the intestine passes dorsal to the ovary to reach the anus at the
posterior end. The large, conspicuous cloacal chamber (or stercoral pocket) opens
into the posterior end of the midgut. The gut posterior to the cloacal chamber is the
hindgut, or rectum. The hindgut is ectodermal, like the foregut, and lined with
cuticle. Posterior digestive ceca open from the midgut and fill much of the space in the
abdomen. Most of the posterior digestive cecum is dorsal to the ovary.
Nervous System
The large nerve ring is the easily recognized white mass in the center of the
cephalothorax (Fig 5). It consists of a brain, or supraesophageal ganglion, lying on the
dorsal surface of the posterior esophagus and a much larger subesophageal
ganglion ventral to the esophagus. The two are connected by paired
circumesophageal connectives which lie out of the plane of section.
The segmental ganglia, which in primitive arthropods are arranged along a
ventral nerve cord, in spiders have moved anteriorly and are concentrated in the
subesophageal ganglion as part of the nerve ring. There is no nerve cord and the
many peripheral nerves arise from the nerve ring to serve the body. The optic nerve to
the eyes enters the brain anteriorly and a largeabdominal nerve exits the posterior end
of the subesophageal ganglion and runs along the ventral edge of the intestine, through
the pedicel, to the abdomen (Fig 5).
Hemal System
The hemal system and excretory systems in the cephalothorax are difficult to
demonstrate in preserved material. The space surrounding the viscera is
the hemocoel.
The heart is a large curved tube in the anterior dorsal region of the abdomen
(Fig 5, 18-20). Anteriorly it narrows to form the anterior aorta passing through the
pedicel to the cephalothorax. Posteriorly it becomes the posterior aorta opening into
the posterior abdomen. Its walls bear ostia and it is supported by alary ligaments.
An aorta extends from the heart in the abdomen to supply the hemocoel with
blood but it is usually not evident.
Excretory System
The single pair of small coxal glands are in the cephalothorax but you probably
will not see them. The chief excretory organs are a pair of very long, narrow
Malpighian tubules in the abdomen but they are usually not demonstrable in these
dissections or preserved animals. They open into the cloaca and are midgut
(endodermal) derivatives.
Reproductive System
The most conspicuous feature of a sagittal section of the abdomen is usually
one of the two ovaries (Fig 5, 18-20). The ovary is a long white organ in the middle of
the abdomen. Its walls bear distinctive vertical folds and eggs are clearly visible within
it. It connects with the female gonopore at the base of the epigynum via an oviduct (Fig
18-29).
Silk Glands
A wide variety of different kinds of silk glands can be seen ventral to the
ovary. Each connects to spigots on the spinnerets via ducts (Fig 18-20). Silk glands
are not muscular and is pulled, or drawn, out of the spigots as the abdomen is moved
away from an attachment point. Silk is composed of the protein fibroin and is
comparable to nylon in strength. It is liquid when extruded but solidifies when placed
under tension by the “drawing out” process. An orb weaver, such as Argiope, has
many different kinds of silk, each secreted by a different kind of gland. Six types of silk
glands are known in spiders.
Natural History
The familiar orb web of the araneid spiders is a complicated construction
consisting of five main regions. If you have access to an orb web, use the following
description to study its anatomy (Fig 18-24, 18-33C).
1. The central hub consists of an irregular network of threads near the center
of the web. The spider spends most of her time in the hub. 2. A set of radial
threads radiates outward from the hub to the frame. 3. A frame of single threads
attached to vegetation, or other features of the environment, extends around the
periphery. The radial threads attach to it. The frame is the part most distant from the
hub and the two are connected by the radial threads. 4. The catching spiral is a sticky
thread that spirals outward from just outside the hub to the periphery of the web. It
crosses the radial threads repeatedly at close intervals. It creates the meshwork of
closely spaced threads in which flying insects are caught. The catching spiral is
the only part of the web that is sticky. Look closely at the sticky spiral, with a hand lens
if possible. The tiny droplets of sticky fluid are easily seen. Gently touch one of the
sticky threads and note its interaction with your finger. Try the same with the other
parts of the web and note the difference. The spider never touches this thread (after
spinning it). She uses the radial threads when she wishes to move across the web. 5.
Between the hub and the catching spiral there is a free zone consisting solely of radial
threads. There is no sticky spiral here so the spider need not worry about catching
herself. In this zone the spider can pass safely through the plane of the web from one
side to the other.
Argiope aurantia and a few other species include a distinctive, zig-zag band of
white silk threads in the hub and free zone and for this reason is called the "writing
spider". This structure is the stabilimentum which has been shown to serve as a
conspicuous marker to prevent birds from flying through the web and destroying
it. Stabilimenta are found only in the webs of those relatively few spiders, of
which, Argiope is one that leave the web up during the day. Most spiders eat the web
before daybreak and spin a new one the following night and thus are not endangered by
flying birds. When threatened Argiope displays a characteristic alarm response which in
which she rocks the web back and forth, presumably to make capture by a predator
more difficult.
The female Argiope prepares a large brown, silken cocoon of eggs in the fall
and usually dies shortly thereafter although she may live long enough to produce a
second cocoon. The eggs hatch in winter but remain in the cocoon until
spring. Juveniles emerge and grow during the summer and are adults by fall. The life
span is one year.
Laboratory Behavior
Living Argiope can be maintained in large glass aquaria or other enclosures in
the laboratory where some aspects of their behavior including web construction, prey
capture and handling can be observed.
Conclusion Questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
How are the appendages of the chelicerates divided?
What are the characteristics of arachnida?
What are the pedipalps used for?
What is the function of the chelicerae?
What is the function spinneret?
What type of respiratory system do spiders have?
How is poison injected into the spiders prey?
What are the organs of the spiders digestive system?
What makes up the spiders nerve ring?
How does the silk gland work?
Describe the web of a garden spider.