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The great redback invasion of Brisbane

The redback is something of an Aussie icon - every Australian child is taught to be wary of this small, but lethal, spider with the distinctive red stripe on its back.

In the late 1980s, researchers at the Queensland Museum began to notice a dramatic increase in reports of redback spiders in Brisbane.

The cause of this population explosion was unknown, but the suspicion was that Australian redbacks were cross-breeding with the newly arrived brown widow spider, enabling the hybrid offspring to thrive in places they previously hadn't.

The redback's favourite haunts are also human habitats — your garden shed, the brick walls of your house, and in the hot metallic corners of playground equipment and even shipping containers.

This 1990 story from the ABC's Quantum program covered early efforts to understand the causes of Brisbane's redback invasion. The concern was that a hybrid form of the spider could not only become more venomous, but also adapt to new habitats where humans might not expect to encounter them.

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2015 update

The hybrid spider theory was ultimately abandoned in favour of another culprit. The moist, sub-tropical climate of Brisbane is not ideal for the spiders, but the late 1980s were unusually dry, which is now thought to be the prime reason for Brisbane's redback explosion.

The arrival of the very wet summers of 2010 and 2012 led to a marked decline in the Brisbane population of both redbacks and brown widow spiders.

But the research had an unexpected outcome — it ultimately led to the discovery that while redbacks are native to Australia, they are not native to the whole of the country.

Their original home was in the south and southwest of Western Australia, where they are perfectly adapted to the dry Mediterranean summers. Their 'colonisation' of the rest of Australia coincided with the spread of European settlement, which made it easy for the spiders to 'hitch' rides into new territories. (The first recorded redback spider bite was in Adelaide in 1849)!

Redbacks are still superb travellers. In 1995 they were discovered in Japan and are now found from Osaka to Tokyo, where they are known as the 'Samurai redback'.

This video is also available on YouTube, via ABCScienceOnline

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