The family of Orb-Weaver
Spiders is unusual in showing a marked size difference between the
two sexes. The bodies of the males are only 6mm long but the females
are giants, with bodies up to 50mm long and leg-spans reaching 200mm
or more. Populations living further from the equator tend to be smaller,
possibly because of the shorter growing season.
The females build large webs, in open areas often high in forests.
The web is a vertical oval made up of a golden spiral bridged by
colourless radiating threads; the oval is suspended by colourless
threads from the surrounding vegetation (or structures) which may
be meters away.
These spiders eat flies, beetles, butterflies and other flying insects
that become ensnared in their webs. Leftovers of meals, such as the
exoskeletons (skins) of insects are left hanging in the web (and
are visible in the photograph).
E.J. Banfield, a naturalist who lived on Dunk Island in Queensland,
wrote in 1918 about indigenous people using these webs for fishing.
The end of a stick was twisted in the web to attach the web to it,
then the stick was waved about to spin the web into a single line
about a metre long. The spider was squashed onto the end of the line
and trailed in the water. Fish that attacked the bait became attached
by their mouths and were taken. The breaking strain of the line was
estimated at about 0.3kg but this was of no real consequence because
the fish that were being caught were only about 4cm long. However,
the method was successful enough to yield 17 fish in 10 minutes of
Spider silk is highly elastic and very strong for its weight. Different
types of silk are exuded from different glands in the abdomen. In
the web of the Golden-Orb Spider, the golden spiral is sticky but
other threads are not. Silk is exuded as a liquid but quickly solidifies,
remaining highly elastic and very strong for its weight. Because
of these unique properties, many laboratories are working on production
of this silk by genetic engineering.
Reproduction in the Orb-Weaver Spiders is not a
straightforward affair. The web is occupied by a single female and
several hopeful males. Although it might not be true of Nephila
pilipes, in the
related species, Nephila plumipes, 60% of males are eaten
during or after sex! It appears that the larger males are more likely
to be eaten, which probably explains their small size. However, males
that have been eaten generally have copulated for longer, so that
more of their sperm fertilize eggs. These males leave more offspring,
passing on more genes into the next generation and contributing to
their biological success.
In Nephila fenestrata, some males copulate with females that are
preoccupied with feeding. These males are even more successful because
they have long copulations while the female is eating, thereby transferring
more sperm. Not only this, but they survive the event to defend the
female from fertilization by other males as well as having the opportunity
to mate again!
The female digs a pit in the ground into which she deposits the
fluffy yellow egg sac and covers it with soil and leaves. After hatching,
the spiderlings quickly make their way up trees and other structures.
This species was first described by the Danish entomologist, Johan
Fabricius, in 1793. A pupil of Linnaeus, the Swedish scientist who
devised the basis of modern biological classification, Fabricius
went on to become a professor at the University of Kiel (which was
in Denmark at that time), publishing several important works on insects.
The Golden-Orb Spider is found in the northern parts of Australia
as well as in South-East Asia and in the Papua-New Guinea region.