The typical orb-weaver spiders are the most common group of builders of spiral wheel-shaped
webs often found in gardens, fields and forests. Their common name is taken from the round
shape of this typical web, and the taxon was formerly also referred to as the Orbiculariae.
Orb-weavers have eight similar eyes, hairy or spiny legs, and no stridulating organs.
The Araneidae family is cosmopolitan, including many well-known large or brightly colored
garden spiders. The 3,006 species in 168 genera worldwide make Araneidae the third-largest
family of spiders known. The orb-weavers include over 10,000 species and make up about 25%
of spider diversity. However, orb-webs are also produced by members
of other families. The large golden orb-weavers and the long-jawed orb weavers were formerly
included in the Araneidae; they are indeed closely related to them, being part of superfamily
Araneoidea. Their webs are similar to those of the typical orb-weavers, but tend to be
less sophisticated and often have an irregular instead of a neat spiral arrangement of the
prey-capturing threads. The cribellate or hackled orb-weavers belong to a distinct superfamily
of the suborder Araneomorphae; their webs are often very sophisticated, but Uloboridae
use neither venom to kill their prey, nor sticky threads in their web, and probably
evolved the orb structure independently. Uloboridae are cribellate, and their threads can be recognized
by the fuzzy and dull appearance, which captures prey by a velcro-like mechanism.
The orb-web
Generally, orb-weaving spiders are three-clawed builders of flat webs with sticky spiral capture
silk. The building of a web is an engineering feat, begun when the spider floats a line
on the wind to another surface. The spider secures the line and then drops another line
from the center, making a "Y". The rest of the scaffolding follows with many radii of
nonsticky silk being constructed before a final spiral of sticky capture silk. The third
claw is used to walk on the nonsticky part of the web. Characteristically, the prey insect
that blunders into the sticky lines is stunned by a quick bite, and then wrapped in silk.
If the prey is a venomous insect, such as a wasp, wrapping may precede biting.
Many orb-weavers build a new web each day. Most orb-weavers tend to be active during
the evening hours; they hide for most of the day. Generally, towards evening, the spider
will consume the old web, rest for approximately an hour, then spin a new web in the same general
location. Thus, the webs of orb-weavers are generally free of the accumulation of detritus
common to other species, such as black widow spiders.
Some orb-weavers do not build webs at all. Members of the genera Mastophora in the Americas,
Cladomelea in Africa, and Ordgarius in Australia produce sticky globules, which contain a pheromone
analog. The globule is hung from a silken thread dangled by the spider from its front
legs. The pheromone analog attracts male moths of only a few species. These get stuck on
the globule and are reeled in to be eaten. Interestingly, both types of bolas spiders
are highly camouflaged and difficult to locate. The spiny orb-weaving spiders in the genera
Gasteracantha and Micrathena look like plant seeds or thorns hanging in their orb-webs.
Some species of Gasteracantha have very long, horn-like spines protruding from their abdomens.
One feature of the webs of some orb-weavers is the stabilimentum, a crisscross band of
silk through the center of the web. It is found in a number of genera, but Argiope,
which includes the common garden spider of Europe, as well as the yellow and banded garden
spiders of North America, is a prime example. The band has been hypothesized to be a lure
for prey, a marker to warn birds away from the web, and a camouflage for the spider when
it sits in the center of the web. However, recent research suggests the stabilimentum
actually decreases the visibility of the silk to insects, thus making it harder for prey
to avoid the web. The orb-web consists of a frame and supporting radii overlaid with
a sticky capture spiral, and the silks used by orb-weaver spiders have exceptional mechanical
properties to withstand the impact of flying prey.
The orb web derived from substrate-bound web, likely an irregular ground web or brushed
sheet web. The change from a ground web to an aerial web allowed for both horizontal
and vertical orb webs that could capture flying prey. During the Cretaceous, a radiation of
angiosperm plants and their insect pollinators occurred. Fossil evidence shows that the orb
web was in existence at this time, which permitted a concurrent radiation of the spider predators
along with their insect prey. The capacity of orb webs to absorb the impact of flying
prey led orbicularian spiders to become the dominant predators of aerial insects in many
ecosystems. Insects and spiders have comparable rates of diversification, suggesting they
co-radiated, and the peak of this radiation occurred 100 Mya before the origin of angiosperms.
Vollrath and Selden make the bold proposition that insect evolution was driven less by flowering
plants than by spider predation – particularly through orb webs – as a major selective
force. Most arachnid webs are vertical and the spiders
usually hang with their head downward. A few webs, such as those of orb-weaver in the genus
Metepiera have the orb hidden within a tangled space of web. Some Metepiera are semisocial
and live in communal webs. In Mexico, such communal webs have been cut out of trees or
bushes and used for living fly paper. Natural history
The oldest known true orb-weaver is Mesozygiella dunlopi, from the Lower Cretaceous. Several
fossils provide direct evidence that the three major orb-weaving families, namely Araneidae,
Tetragnathidae and Uloboridae, had evolved by this time, about 140 million years ago.
They probably originated during the Jurassic. Based on new molecular evidence in silk genes,
all three families are very likely to have a common origin.
The two families, Deinopoidea and Araneoidea, have similar behavioral sequences and spinning
apparatuses to produce architecturally similar webs. The Araneidae weave true viscid silk
with an aqueous glue property, and the Deinopoidea use dry fibrils and sticky silk. The Deinopoidea,
have a cribellum – a flat, complex spinning plate from which the cribellate silk is released.
They also have a calamistrum – an apparatus of bristles used to comb the cribellate silk
from the cribellum. The Araneoidea, or the "ecribellate" spiders, do not have these two
structures. The two families of orb-weaving spiders are morphologically very distinct,
yet there is much similarity between their web form and web construction behavior. The
cribellates retained the ancestral character, yet the cribellum was lost in the escribellates.
The lack of a functional cribellum in araneoids is most likely synapomorphic. If the orb-weaver
spiders are a monophyletic group, the fact that only some species in the group lost a
feature adds to the controversy. The cribellates are split off as a separate taxon that retained
the primitive feature, which makes the lineage paraphyletic and not synonymous with any real
evolutionary lineage. The morphological and behavioral evidence surrounding orb webs led
to the disagreement over a single origin or a dual origin. However, molecular analysis
provides more support for a monophyletic origin. Systematics
The categorization into subfamilies and tribes follows Joel Hallan's Biology Catalog.
The Nephilidae have been elevated to family status in 2006. Some researchers also consider
the genera Leviellus, Parazygiella, Stroemiellus and Zygiella to reside in the family Zygiellidae.
Araneinae Simon, 1895
Anepsiini Arachnurini
Araneini Arkycini
Bertranini Celaenini
Cyclosini Dolophonini
Exechocentrini Heterognathini
Hypognathini Mangorini
Poltyini Pseudartonini
Testudinarini Ursini
incertae sedis
Glyptogona Simon, 1884
Argiopinae Cyrtarachninae Simon
Cyrtarachnini Simon Mastophorini
Cyrtophorinae Gasteracanthinae
Caerostrini Gasteracanthini
Micratheninae incertae sedis
Artonis Simon, 1895 Colphepeira Archer, 1941
Enacrosoma Mello-Leitão, 1932 Encyosaccus Simon, 1895
Melychiopharis Simon, 1895 Micrepeira Schenkel, 1953
Parmatergus Emerit, 1994 Pronous Keyserling, 1881
Sedasta Simon, 1894 Singafrotypa Benoit, 1962
Tethneus Scudder, 1890 †
Tethneus guyoti † Tethneus henzii †
Tethneus robustus †
See also
List of Araneidae species Spider families
References
Further reading The Life of the Spider by John Crompton. Mentor,
1950. "The Orb-Weaving Spiders of Canada and Alaska.
Araneae: Uloboridae, Tetragnathidae, Araneidae, Theridiosomatidae. Insects and Arachnids of
Canada Series, Part 23." By C. D. Dondale, J. H. Redner, P. Paquin, and H. W. Levi. NRC
Research Press, Ottawa, 2003. ISBN 978-0-660-18898-0 How to Know the Spiders by B. J. Kaston. Dubuque,
1953. Spiders by Barbara York Main. Sidney, 1976.
Biology of Spiders, by Rainer F. Foelix, second edition, 1996
Levi, H. W.: The new orb-weaver genus Lewisepeira. Psyche 100: 127–136. PDF
Platnick, Norman I.: The world spider catalog: Araneidae, version 11.5. American Museum of
Natural History. External links
Spiders of Australia Spiders of northwestern Europe
Araneae, Arachnology Home Pages World Spider Catalog
Orb weavers of Kentucky, University of Kentucky Pictures of Mangora species
Gasteracantha cancriformis, spinybacked orbweaver on the University of Florida / Institute of
Food and Agricultural Sciences Featured Creatures website
Neoscona crucifera and N. domiciliorum on the University of Florida / Institute of Food
and Agricultural Sciences Featured Creatures website HOE