DON鈥橳 brush away those cobwebs, especially if you suspect pollution may be affecting your health. Certain spiders鈥� webs turn out to be so good at trapping fine particles from the air that they make ideal detectors for toxic pollutants such as heavy metals and dioxins.
Grant Hose, an eco-toxicologist with the New South Wales Environment Protection Authority, made the discovery while studying the webs of spiders that live in the Grand Arch of the Jenolan Caves in the Blue Mountains in New South Wales, one of Australia鈥檚 oldest tourist attractions.
This limestone arch is 120 metres long and has a road running through it. Hose, who ran the study while at the University of Technology in Sydney, found that zinc and lead levels in the webs in this arch were 2 to 10 times as high as those in nearby caves.
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It wasn鈥檛 only metals the webs accumulated. In another cave, the Abercrombie Arch, the webs contained 3 times as much phosphate as those in the Grand Arch. 鈥淎bercrombie has a large swallow population so you鈥檇 expect that with all the guano,鈥� says Hose. His results will be reported soon in the journal Environmental Pollution.
Not all spiders鈥� webs make useful pollution monitors. The ones Hose and his team analysed were built by two species of spider that belong to a group called cribellates, which includes many common species such as house spiders. Unlike traditional 鈥渨heel鈥� webs, which trap prey using sticky silk threads, cribellate webs are made from matted microscopic fibres that entangle their prey. This structure also makes them particularly good at trapping particulate pollution, says Hose鈥檚 colleague Mike Gray from the Australian Museum in Sydney.
But the high levels of pollution could spell bad news for one species of spider. The only known population of Badumna socialis lives in the limestone arches of the Jenolan Caves. Unlike most spiders, they are not solitary creatures. They build their webs alongside one another, creating massive blue-grey sheets of shimmering silk across the cave roofs. Ironically, the spiders鈥� cleanliness could be the death of them.
鈥淪piders groom themselves assiduously so it鈥檚 likely that they are ingesting contaminated material, and the dust makes their webs less useful as traps,鈥� says Gray. The pollution Hose found could put the entire population in the Grand Arch at risk. The Jenolan Caves Reserve Trust is now looking at ways to curb traffic through the arch to cut the pollution.
Hose believes that webs made by cribellates could now be used as biosensors. And unlike traditional means of monitoring airborne particulate pollution, spiders鈥� webs are cheap, renewable and found everywhere from the inside of houses to the sides of roads.
鈥淚t鈥檚 a great idea for reconnaissance over a broad area,鈥� says Robin Ormerod, deputy president of the Queensland branch of the Clean Air Society of Australia and New Zealand. 鈥淚t lets you look for hot spots you can investigate further with more sophisticated apparatus.鈥�