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 observation.
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.