Last November a group of science students from the Abu Dhabi Indian
School discovered a dense colony of several dozen orb-weaving
garden spiders. I was guiding them through Bateen Wood, roughly
35 hectares of semi-wild plantation on Abu Dhabi Island. The discovery
created a good deal of excitement, because few of us had seen
more than an occasional spider in the past. In fact, I habitually
visit the wood for birdwatching, but I had never seen spiders
there, being intent on other subjects.
The orb weavers are perhaps the best known of all 32,000 + species
of spider. These creatures fascinated human beings since ancient
times, and many people fear them. Close observation would lead
one to the wise conclusion that the garden spider need only be
feared by small insects.
The female spider begins as a faintly marked immature, but she
develops into a beauty after several moultings. At maturity, the
legs are banded with alternately dark and light lines the width
of a blunt pencil lead, with an underlying reddish colour during
breeding. Her abdomen is likewise banded, with the light bands
tinged with pale yellow; the cephalothorax is a pale yellowish
brown, with four beady, black eyes attached. The underside of
the spider, where the silk-producing spinnerets are located, is
brightly marked with a red patch and two yellow stripes.
Mature females measure about 1 inch (25 mm), from pedipalps to
tip of abdomen, and hang head downward in a tightly woven web,
which usually has vertical, zig-zag markings called stabilimenta.
Looking closely, one sees the much smaller, brown male – about
1/2 inch (12mm) long at maturity. Mature males are found within
the web of the female or within barrier webbing, a warning and
stabilizing structure found among webs of mature females.
By mid-December, the spider colony has produced offspring, brown
spiderlings the size of mustard seed suspended within a nest of
golden silk. Hundreds of spiderlings take to the air, ballooning
to a new home on a fine silk strand. Earlier generations probably
flew into this wood as youngsters, possibly from Iran or Jordan
during a strong, spring storm.
Life is dangerous for such tiny weavers, Besides the possibility
of becoming prey to one another, they are also eaten by dragonflies,
lizards, and birds, as well as toads in other locations. Warblers
feed on them and also use the spiders’ silk to line their nests
in spring. In the fine winter weather, the spiderlings prosper,
but heat is a severe limitation in the summer months.
The tall grasses and densely shaded areas under bushes and trees
provide the essential habitat requirements of moist mulch and
shade, as well as harbouring nourishing insects. Mowing in Bateen
Wood would drastically reduce the spider population. Therefore,
this must be done in a planned manner, leaving grassy patches
for the survival of this and other species of arachnid.
Over the winter months, this garden spider lives prima-rily on
the clumps of rushes within the wetter areas of the wood. Such
creatures as mosquitos, ants, and leafhoppers are caught and eaten
by the spiderlings. Besides grasshoppers and cockroaches, the
Balkan pierrot (Taurus balkanicum), Lederer’s cupid (Chilades
galba) and related butterflies are important nourishment for mature
spiders.
The typical orb weaver eats about twice its own body weight in
insects every day (not to mention those caught but not eaten),
approximately 2000 insects within the single year of its life
cycle. Multiplying this by the hundreds or thousands of spiders
found in a well managed woodland, it becomes clear that Argiope
helps provide a balanced ecosystem. In fact, farmers around the
world are increasingly turning to these creatures as beneficial
predators, because they primarily eat destructive pests rather
than beneficials, as reported by Jill Jesiolowski and Dr. Susan
Riechert in Organic Gardening , (July/August 1995 issue).
In early May, when the fall hatchlings were half-grown, I stumbled
across a few mature females, one with glowing red legs. She was
encircled by six, mature males! This is considered an indication
that the female is typically non-aggressive to the male when mating.
The fact that most males (those little socialites!) abandoned
spinning silk in favour of sitting at the edge of a female’s web
seems to support that idea.
Obviously, the May date for these few spiders was the end of their
life cycle. Therefore, the spiders have been in Arabia long enough
to have overlapping generations, rather than one per year. The
warm climate is undoubtedly the reason for this, a real boon for
anyone interested in studying spiders.
As the temperatures increase during the summer months, the rushes
are abandoned in favour of shadier places. Hopefully, as the temperatures
drop in autumn, the beautiful banded females and their smaller
male consorts shall return to a prominent perch for all of us
to study and enjoy.
Author’s Note: Thanks to H. E. Mohammed Fadhil al Hameli, Assistant
Undersecretary of the Abu Dhabi Municipality, Bateen Wood has
been designated as a protected wildlife area and outdoor classroom,
overseen by the National Avian Research Centre (NARC). Little
is known about the hundreds of various arachnids found in Arabia.
currently, arachnid specialists Norm Platnick and Lou Snorkin
of the American Museum of Natural History in New York, as well
as Barbara Tigar, entomologist for NARC, are studying this species
and hundreds of others from the United Arab Emirates.