These spiders are widely distributed in forest, woodland and heathland habitats across eastern Australia, from Tasmania to southern Queensland (QLD, NSW, VIC, TAS).Features:
These slender, long-legged spiders have eight eyes, two of which are enormously enlarged, placed centrally on the prosoma or "head"; they face forwards, looking rather like searchlights. Females reach 25 mm in body length and are light salmon-brown above; the abdomen bears two low humps midway along the sides and has small orange patches underneath. Males are shorter and thinner (about 10 to15 mm in body length) with spindly legs; the body has dark and light grey longitudinal stripes above and a pair of small white horns on the head over the eyes.Ecology/Way of Life:
Net-casting spiders are common in bushland and gardens. By day they hide, stick-like, among foliage. At night they build beautiful little webs of thick, bluish-white cribellate silk about the size of a postage stamp. The way the spider spins the web, and its structure, show that the net is a highly modified orb web, and that net-casting spiders are descended from orb-weaving ancestors.
These little nets are made among low vegetation, usually above a broad, flat surface across which prey animals are likely to walk, such as a broad leaf, a piece of bark, a tree trunk or even the ground. After spinning its web the spider deposits some spots of white faeces on this surface as aiming points. The spider hangs upsidehead down from its trapeze of silk, holding the net in its front pairs of legs, and waits. Its enormous eyes gaze downwards, watching for prey movement across the white aiming spots.
These large eyes provide outstanding low-light night vision. Their compound lenses (F number of 0.58) can concentrate available light very more efficiently than a cat (F = 0.9) or an owl (F = 1.1). The image is focussed onto large light receptive retinal areas. The receptive part of these areas is formed anew each evening, and broken down again at dawn.
When an animal such as an insect passes below, the spider opens the stretchy web to 2 to 3 times its resting size and lunges it downward over the unsuspecting prey. The sticky cribellate silk net envelopes the insect, which is then rapidly bitten and wrapped. While eating its catch, the spider may start making a new net for its next meal. Prey animals include cockroaches, ants, spiders and even moths - net-casters seem sensitive to air currents and will lunge the net towards aerial prey. Prey as large as male trapdoor spiders and gryllacridid wood crickets are taken.
Net-casting spiders mature in summer, with mating and egg-laying taking place into autumn. The male attaches a mating thread to the female's net support lines and jerks it to entice her onto it for mating. The egg sacs are round balls, 9 to 10 mm in diameter, covered with a tough, closely woven layer of salmon-brown silk flecked with black. The sacs are suspended on vegetation and disguised with twig and leaf litter detritus. Up to four sacs may be produced. The dark brown spiderlings emerge in spring and look like a cloud of little anchors (a narrow body and extended front legs) hanging in silk lines above the egg sac. In 5 to 6 weeks they start building their own tiny nets.Interaction with Humans/Threats:
No interactions with humans or threats to net-casters have been identified. However, the structure and function of the eyes in these spiders may be worthy of further investigation, given that the eyes of these spiders are able to concentrate light more effectively than cats or owls, and are capable of rapid replacement of light receptive tissue daily.Other Comments:
This species was described by L. Koch in 1878; the genus name is derived from the Greek deinos = fearful, and opis = appearance, which reflects the common family name of ogre-faced spiders; the species name is formed from the Latin: sub = somewhat and rufus = reddish.Further Reading:
http://www.ucmp.berkeley.edu/people/motani/ichthyo/eyes.html for information on vision and light collection in various animals.
Austin, A.D. and Blest, D.A. (1979). The biology of two Australian species of deinopid spider. Journal of Zoology, London 189: 145-156.
Clyne, D. (1967). Note on the construction of the net and sperm web of the cribellate spider Dinopis subrufus (Koch) (Araneidae: Dinopidae). Australian Zoologist 14: 189-197.
Coddington, J.A. (1986). Orb webs in "non-orb" weaving ogre-faced spiders (Araneae: Dinopidae): a question of genealogy. Cladistics 2: 53.
Mckeown, K.C. (1963). Australian Spiders. Angus and Robertson.Topics: Spider webs Silk Prey capture Vision
Text & map by Mike Gray; photographs by Mike Gray, courtesy of the Australian Museum.Sponsorship welcomed:
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