The Find-a-Spider Guide

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Garden orb-weaver

Fact Box
Species:
Eriophora transmarina (QM)
Previous species name:
Araneus transmarinus
Family:
Araneidae
formerly Argiopidae
Body length:
female: 24 mm
male: 16 mm
Habitat:
In a vertical orb-shaped web between branches of shrubs; the spider usually repairs and sits in its web only in the evenings and waits with its legs extended for prey to blunder into the web. When this happens the spider rapidly wraps it up in silk.
Toxicity:
Uncertain; may cause mild illness but this spider is not very aggressive to humans and tries to escape if approached
Eriophora transmarina
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Plain coloured
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Striped example
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Side view
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In web at night
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Egg mass
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Female epigynum
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Spotted female
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Camouflage colours

The female is somewhat larger than the male, which tends to wait on the edge of the web. An unusual feature of the female is the variation in colour and patterning on the upper surface of its shield-shaped abdomen. Some individuals have a white or reddish longitudinal stripe down the centre of the abdomen while others have almost no abdominal patterning. The appearance of the male is so different it looks like it is another species.

A useful identifying feature on a female is the long, needle-like part (called a scape) of its epigynum which points backwards towards the spinnerets. During the day the female hides in a leafy retreat (or under a ledge on a building) near the top of the web with its legs drawn up against its carapace. Egg masses are sometimes seen anchored near the female's retreat and have the appearance of a mass of fluffy webbing that is off-white to grey-green in colour.

Please note that the photos shown on this page are thought to be those of Eriophora transmarina as described by VT Davies (Queensland Museum) in 1980 but it is now clear that some or all of them could instead be Eriophora biapicata which Davies also named. The descriptions given by Davies for these species are now very difficult to access but it is generally agreed that the males and females of both E. biapicata and E. transmarina are so similar in appearance (both varying greatly in surface markings from specimen to specimen) that the two species can only be distinguished by a careful comparison of their genitalia. Indeed, there is some justification for suggesting they are not separate species but are actually part of what should be referred to as the 'Eriophora transmarina complex'. However, at the present time E. transmarina is claimed to be the species most likely to be found in Northern Australia (never south of Sydney) but not in arid regions whereas E. biapicata is the more common species in Southern Australia and in the arid centre of the continent. Unfortunately, the ranges of these two species overlap in South Queensland and Northern NSW.

Nature notes: This kind of spider is never likely to be found inside a house or other building although it might perhaps string its web from a suitable support on an open veranda or porch. Because the entire vertical web can be constructed in a single night the householder may be surprised to find it there one morning. However, the spider itself will probably not be in evidence since the normal practice of Eriophora species is to occupy the web only at night and to hide somewhere near the upper supports of the web during the daylight hours. Until it reaches maturity the male will behave like a female but adult males will cease catching insects and will instead go in search of a web that contains a female. This search is facilitated by the detection of a pheromone secreted by the female. If it is not killed by the female during or after mating the male may search for another female but typically dies soon after reaching mturity even if it has never managed to mate. Even the adult female normally dies when the colder months of the year arrive and the supply of insects to feed on diminishes. This of course means the lifetime of an Eriophora specimen is rarely longer than 12 months but before dying the females usually lay at least one batch of eggs before dying so the species is not at risk of becoming extinct because of its short lifetime.

Spider(s) with a very similar appearance: Some other Araneus or Eriophora species, such as Backobourkia brounii, Eriophora biapicata, and Acroaspis tubiculifera.



Email Ron Atkinson for more information.    Last updated 2 March 2020.