Cities making spiders grow bigger and multiply faster

City-dwelling spiders grow larger and could produce more offsprings than their country cousins, according to new research.
City life does not suit everyone but golden orb-weaving spiders thrive in urban landscapes, a University of Sydney study shows.
"City-dwelling orb-weaving spiders grow larger and could produce more offspring than their country cousins our research shows," said Elizabeth Lowe, a PhD candidate in the University's School of Biological Sciences and lead author of the study.
This study shows invertebrates are sensitive to urbanisation but that not all species are negatively affected by living in cities.
"Our findings show the impact urbanisation can have on local wildlife. While many species do not survive encroaching urbanisation and the consequent loss of native habitat, others have a more complex relationship with man-made changes to the landscape," said Lowe.

The researchers collected golden orb-weaving spiders (Nephila plumipes) from across the Sydney city region.

"We quantified the degree of urbanisation of 20 sites then looked at changes in the spiders' body size, fat reserves and ovary weight," Lowe said.
The results show spiders in areas with more vegetation cover had smaller bodies and larger bodies when located in urbanised areas, characterised by increased housing and population density and hard surfaces such as roads and buildings.
The authors also found that the spiders' reproductive ability, measured by increased ovary weight, appeared to increase in urban areas.
"Two reasons likely to explain the differences between these spiders in urban and non-urban environments are temperature and prey availability," said Lowe.

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. Higher temperature is associated with increased growth and size in invertebrates.
"Urban lighting also may be a contributing factor as it attracts insects and means more food for spiders in those environments. This increase in prey would result in bigger, heavier, more fecund spiders," said Lowe.
The study was published in the journal PLOS.