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Latrodectus hasseltii (Family Theridiidae)

Redback Spider

Distribution:

Redback Spiders are widespread in Australia in a range of habitats, from open forest to shrubland. We are familiar with them because they are very successful in adapting to disturbed urban and rural habitats. They belong to a world-wide group that includes the American Black Widow Spider(QLD, NSW, VIC, ACT, TAS, SA, WA, NT).

Features:

Features: The red and glossy black colour pattern of the female Redback Spider (about 10 mm in body length) makes it easily recognisable, although a duller lighter brownish -body and orange-yellow stripe colour is sometimes seen. The red stripe may be whole or broken and flanked by fine white lines. A reddish "hourglass" marking is always present underneath the abdomen. At first, juvenile females have more white colouring and a striped appearance. Males are small (3 to 4 mm body length), and retain a 'juvenile' colour pattern.

Ecology/Way of Life:

Redbacks build webs anywhere that provides a sheltered retreat area, adequate warmth for breeding and a plentiful supply of food. Their webs might occupy a small space under a rock or have traplines that extend 1to 2 metres to the ground under a shearing shed floor. Large populations can build up where food and web sites are abundant, ranging from junk-strewn, overgrown suburban yards to cave entrances on the Nullarbor Plain.

The web consists of an upper, thimble-like retreat of tough strong silk and a central network of threads that support a "forest" of vertical, sticky traplines descending to the ground ("the gum-footed web"). Walking prey, ranging from ants and beetles to spiders and skinks, become entangled in the sticky lines. The spider positions itself above the struggling prey and uses barbed spines on its back legs to throw out bands of sticky silk from the spinnerets. This swathing silk immobilises the prey which can then be bitten safely. Female spiders live for 2-3 years. They make from 4-10 round, fawn coloured egg sacs, each with from 40 to more than 500 eggs. Spiderlings are cannibalistic and will eat unhatched eggs and other spiderlings before dispersing. They disperse mainly by aerial ballooning, although adults and young may be transported on vehicles and in cargo, some as far afield as Japan.

The web consists of an upper, thimble-like retreat of tough strong silk and a central network of threads that support a "forest" of vertical, sticky traplines descending to the ground ("the gum-footed web"). Walking prey, ranging from ants and beetles to spiders and skinks, becomes entangled in the sticky lines. The spider positions itself above the struggling prey and uses barbed spines on its back legs to throw out bands of sticky silk from the spinnerets.spurts out sticky silk from enlarged spigots on its posterior spinnerets and uses barbed spines on its back legs to throw out swathing silk, so This swathing silk immobilisesing its the prey which can then be bitten safely. before biting it. Female spiders live for 2-3 years. They make from 4-10 round, fawn coloured egg sacs, each with from 40 to more than 500 eggs. Spiderlings are cannibalistic and will eat unhatched eggs and other spiderlings before dispersing. They disperse mainly by aerial ballooning, although adults and young may be transported on vehicles and in cargo, some as far afield as Japan.

Mating in Redback Spiders is characterised by sexual cannibalism. After a complex courtship routine, the male perches on the female's underside and inserts one of his palpal mating organs into her abdominal genital opening. He then somersaults through 180? so that his abdomen rests against the female's fangs. As he inseminates her,. Sshe then begins to chew eat the end of his abdomen as he inseminates her. After 5-30 minutes of this, the mutilated male retreats onto the web, only to return and repeat the whole process using the other mating organ. This time he is either completely killed eaten by the female or dies soon after. This selfless behaviour may ensure that the sacrificed male maximises his sperm input and the female's fertility.

Interaction with Humans/Threats:

Up to 400 people are treated each year with antivenom for Redback bites. Only the female is dangerous, as the fangs of the male are too small to penetrate human skin. The 13 recorded deaths occurred before 1956, when an antivenom was introduced. No special first aid is required (but cold packs may alleviate the severe pain that can accompany bites). If serious symptoms develop, they do so slowly over 2 to 3 hours, and medical attention should be sought.

Other Comments:

The species was named by T. Thorell in 1870 for his colleague, A.W.M. van Hasselt. The genus name comes from the Latin latro= robber, and dectes= biter

Further Reading:

Forster, L.M. (1995). The behavioural ecology of Latrodectus hasselti (Thorell) (Araneae: Theridiidae), the Australian Redback Spider: a review. In Australasian spiders and their relatives: papers honouring Barbara York Main (M.S. Harvey, ed.). Records of the Western Australian Museum Supplement 52: 13-24.

Raven R. and J. Gallon (1987). The Redback Spider. In Covacevich, J., Davie, P., Pearn, J. (eds), Toxic Plants and Animals: a guide for Australia. Queensland Museum.

Sutherland, S.K. and J. Tibballs (2001). Australian Animal Toxins. The creatures, their toxins and care of the poisoned patient. Oxford University Press.

Topics: Spider webs Venom Sexual cannabilism Altruism Silk Prey capture

Acknowledgments:

Text & map by Mike Gray; photographs by Mike Gray, courtesy of the Australian Museum.

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