Arachnophobes, to whom the mere mention of spiders can bring on a case of the willies, are not likely to be happy to learn that some spiders taking up residence in Australian cities are growing larger than their rural counterparts.
Entomologists at the University of Sydney say a species known as the golden orb-weaving spider is growing larger and having more reproductive success in the country's cities than in rural areas possessing more vegetation.
The finding suggests some species might actually benefit when forced into adapting to new habitats and environments, they say.
Although native to the Australian countryside, the orb-weavers are increasingly being seen in urban areas such as in Sydney in southeast Australia.
There they're rapidly proving to be accomplished urban dwellers, says lead study researcher Elizabeth Lowe of the university's School of Biological Sciences.
"The effects of urbanization on wildlife are very varied -- some do well, others don't," Lowe explains. "Animals which benefit from urbanization are called urban exploiters, and these species (including the spiders from this study) do better in urban areas than their natural habitats."
Orb-weaver spiders, found in most areas of the globe, construct semi-permanent spun webs in which the spend their entire adult life.
Writing in the journal PLOS ONE, the researchers report studying 222 mature female orb-weavers from both small urban parks and larger areas covered with native vegetation.
The spiders from areas with large vegetation cover had smaller bodies while those from urban areas, with higher population density and more housing, had larger bodies.
Lowe said she suspects temperature and an increased availability of prey might explain the size differences.
"Hard surfaces and lack of vegetation lead to the well-known 'urban heat island' effect, with more heat retained than in areas with continuous vegetation," she says.
"Higher temperature is associated with increased growth and size in invertebrates," she notes.
More lighting in urban areas might also be attracting more insects providing food for the spiders, she says, which could also be driving the development of bigger orb-weavers.
While arachnophobes might not consider that an encouraging thing, Lowe says that the spiders' success in urban environments is in fact a good outcome, noting that they will feed on mosquitos and other insects most people find annoying.
"By gaining a better understanding of the impacts of urbanization on wildlife in cities, we can work towards creating healthy, functioning ecosystems in urban areas," she says.
