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Spiders grow bigger when they live in cities

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Itsy-bitsy spiders are not fans of big cities. A new study shows that spiders that live in cities are bigger and thrive better than their country-living counterparts.

Published in PLOS ONE, Australian scientists detailed animals that survive successfully in man-made environments. "Urbanization modifies landscapes at multiple scales, impacting the local climate and changing the extent and quality of natural habitats," the study authors write. But some species, such as birds and rodents, become "urban exploiters" and can adapt to the changing habitat.

Golden orb-weaving spider, known as Nephila plumipes, hang on their home of beautifully-spun webs for their entire lives once they mature, making them the perfect subject for researchers. 

They collected 222 female spiders from different areas of urbanization around Sydney, noting the amount of concrete, grass and leaf-litter cover. The researchers than measured the size, fat reserve and ovaries of the eight-legged spiders to analyze their reproductive capacity.

 They found that the city spiders were supersized, better fed and had more offspring than their country counterparts. Scientists believe that city climates that they describe as "urban heat islands" are the best environments for the spiders to thrive in. 

"Hard surfaces [like buildings, roads and concrete] retain heat, leading to the urban island-heat effect. This increase in temperatures is likely what is leading to increased growth of the spiders," Elizabeth Lowe, lead author of the study says.  

City lights attract insects like a moth to a flame, so spiders in the big city have plenty of meals.  "The increased expenditure and management of parks in wealthy suburbs could result in healthier vegetation patches," the researchers write, "which would increase prey abundance and allow spiders to grow larger and build up fat reserves."

Now that those who live in cities will have to shake their spider heeby-jeebies, it is important to remember that the big city spiders eat small bugs like mosquitoes that are more annoying than the creepy eight-legged crawlers.

The researchers focused on just the golden orb-weaving spider, but the authors of the study say that other species of spiders could also be thriving in urban areas.

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