Cities help spiders grow bigger, multiply faster

UPI Science News, 2014-08-20

Arachnophobic urbanites, you might want to pack it up and head for the suburbs -- safer yet, the countryside. New research suggests many spiders prefer the glitz and glam of the city life. In a recent study, published this week in the journal PLOS ONE, scientists reveal that certain spider species get bigger and multiply faster in urban environs.

It's no secret that urbanization is on the rise. And as human development crops up in new places, landscapes shared with plants and animals are transformed, affecting even invertebrates like spiders. Recently, a team of researchers -- lead by Elizabeth Lowe from the University of Sydney, Australia -- set out to find out exactly how insects might be affected by the expansion of cities.

Much work has been done on the impacts of urban expansion on birds and mammals, but few have looked at insects and specifically at anatomical changes, as Lowe's research did. Lowe and her colleagues compared specimens of golden orb-weaving spiders, or Nephila plumipes, a species common throughout the natural and constructed environs of Australia . What they found was that specimens living in more densely populated areas -- with roads, houses, and other forms of development -- were actually bigger in body size and ovary weight, as compared to their relatives in the vegetation of the country.

"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," Lowe told BBC News . "Higher temperature is associated with increased growth and size in invertebrates."

"Urban lighting may also be a contributing factor, as it attracts insects and means more food for spiders in those environments," Lowe added. "This increase in prey would result in bigger, heavier, more fecund spiders."

Though Lowe and her colleagues think this trend of bigger, more reproductive spiders could hold true for a variety of species, they acknowledge that different kinds of spiders have different habitats and methods of hunting. As well, urbanization in one ecosystem, such as grasslands or forests, won't affect species the same way development in another ecosystem, like desert, will.

Lowe says understanding these nuances and how they will affect different species is important for conservation. "By identifying the elements of cities that influence the success of urban exploiters we gain a better understanding of what drives changes in the biodiversity of urban systems," she told Discovery News .