By Dr Mike Gray and updated by Dr Helen Smith, Australian Museum
An enormous variety of spiders can be seen in the Berowra Valley region. Some of the more obvious are the web builders, especially the orb-web weaving families.
Garden orb weavers
The most familiar spiders are the large grey to reddish-brown ‘garden orb weavers’, Hortophora transmarina and H. biapicata. Occasionally these spiders have a creamy white stripe or spots on the back of the abdomen. Their big wheel-like webs are often seen at night stretched across tracks between shrubs and trees. For insects, these webs are almost invisible and are hard to avoid. Towards morning the spiders usually destroy their webs, except for a few frame lines, by eating the silk. The silk proteins are recycled to the silk glands and used again to make more silk. The spiders shelter among foliage to the side of the web during the day. The sexes are similar in size. The male lures the female from her web onto a special mating thread he has constructed, where mating takes place. Many other orb weavers are found in their webs day and night. One beautiful example, often seen in bushland, is the ‘enamelled spider’, Plebs bradleyi, so called because of its bright glossy abdomen of white, black, red and green. If you see enough of them you will notice occasional striking colour variations of opalescent green or yellow.
Saint Andrew’s cross spider
The ‘Saint Andrew’s cross spider’, Argiope keyserlingi, is another very colourful spider, whose numerous silvery hairs may help reduce body heating during the day. These spiders make themselves additionally conspicuous by decorating their orb webs with ribbons of bright white silk, in a cross or partial-cross shape (one or more of the four arms of the cross may be missing). These webs are usually found among low tree and shrub foliage. The silk ‘cross’ is a strong reflector of ultra-violet light, which is attractive to insects, and it probably helps the spider by luring prey towards the web. The variable structure of the silk cross may also help confuse bird predators searching for a juicy spider meal.
Golden orb weavers
The largest and strongest webs are built by the big ‘golden orb weavers’, of which Trichonephila plumipes is the common species in this region. Their orb webs, built among tall shrubs or slung between trees, have a golden sheen when viewed slantwise. The web is very strong and small birds sometimes become entangled. Webs often have an additional ‘barrier’ network of silk lines, where the spider hangs its prey, and which provides some protection from predators. When these spiders are very numerous, hundreds of webs may form an interconnected ‘colony’, as is sometimes seen in mangrove habitats. In both this and the previous species, the male is much smaller than the female, and mating occurs in the orb web.
These smaller orb weavers leave the upper sector of the web open, and there they place a protective retreat. This retreat is usually a neatly silk-curled gum leaf, even a snail shell. Different leaf curler species can be determined by the distance of the open end of the leaf retreat from the centre of the web. In a common species, Phonognatha graeffei, it is placed right at the centre, but in other species it is further out. The webs are found among understorey shrubs. The sexes are similar in size but a different mating strategy is evident. Males spiders have been found co-habiting in the leaf retreat with immature females; presumably mating occurs as soon as the female matures.
Australian Museum Website: https://australian.museum/learn/animals/spiders/
A guide to the spiders of Australia Volker,W. Framenau, Barbara C. Baehr and Paul Zborowski, New Holland Press 2014.
A field guide to spiders of Australia Robert Whyte and Greg Anderson, CSIRO Publishing 2017