A common orb-weaving spider may grow larger and have an increased ability to reproduce when living in urban areas, according to ecologists from the University of Sydney.

They believe urbanization may drastically alter the landscape, local climate, and consequently the organisms that inhabit it. Some will no longer have the resources they need to survive in the urban environment, while others may thrive, possibly more so than in their native habitat; one way in which this may be evident is in marked changes in the organism's size.

The authors of this study investigated changes in the physical attributes of the orb-weaving spider, commonly found in both urban and natural landscapes, using multiple environmental variables. The researchers quantified the degree of urbanization at multiple sites in Sydney, Australia, and investigated changes in the orb-weaving spider's body size, fat reserves, and ovary weight. 

An orb-weaving spider. Credit: Lizzy Lowe

They determined that the spiders had smaller bodies in areas with more vegetation cover and larger bodies in areas associated with urban development, indicated by the presence of hard surfaces. Additionally, the authors found that the spiders' reproductive ability, measured by increased ovary weight, may have increased in higher socioeconomic areas, such as in areas with hard surfaces or leaf litter. 

According to the authors, the larger size and increased reproductive capacity of orb-weaving spiders in urban areas further support the idea that some species may benefit from habitat changes associated with urbanization.

It may not be as determinate as the ecologists suggest. Many residents of Pennsylvania today had descendants who moved there because they wanted to work in steel mills, they were primarily big eastern Europeans because small people were not getting the jobs. But living in Pittsburgh or Bethlehem did not turn their children large nor improve their reproduction, even though the region became overrepresented with large children.

Citation: Lowe EC, Wilder SM, Hochuli DF (2014) Urbanisation at Multiple Scales Is Associated with Larger Size and Higher Fecundity of an Orb-Weaving Spider. PLoS ONE 9(8): e105480. doi:10.1371/journal.pone.0105480