Spiders living in cities are bigger, healthier and better at reproduction than their country-dwelling counterparts, according to a new study conducted by Australian scientists. So, don’t be surprised if you see spiders in your garden getting bigger. Researchers led by Elizabeth Lowe of the University of Sydney found that female spiders had bigger ovaries and larger bodies in the areas of urban development.
Spiders spend most of their adult life in the webs they build
Findings of the study appeared in the journal PLOS One. Urbanization dramatically alters the local climate and natural landscapes. Researchers were studying the effect of urbanization on wildlife that manage to survive in man-made environment. Expansion of cities usually degrades the natural habitats and many species struggle to survive. But results of the latest study show that some species actually benefit from such changes.
In the past, most research on the effects of urbanization has been focused on birds. And very few studies have looked at anatomical changes in animals. The Golden orb-weaving spiders, Nephila plumipes, are found in urban as well as natural landscapes in Australia. Birds and rodents are mobile organisms. In contrast, spiders build webs upon reaching adulthood where they remain in for their whole adult life.
Scientists collected 222 mature female orb-weaving spiders from urban parks, as well as different areas of native vegetation. They quantified the level of urbanization at the sites before recording the fat reserves, body size and ovary weight of spiders. Researchers found that spiders collected from areas of more vegetation had smaller bodies compared to those from urban areas. Reproductive ability, measured by ovary weight, was higher in spiders from urban areas.
Why spiders growth faster in urban settings?
Elizabeth Lowe attributed these differences to two things: temperatures and easy availability of prey. Buildings, concrete, hard surfaces and lack of vegetation lead to the “urban heat island” effect. That means cities retain more heat than areas with moist earth and continuous vegetation. Invertebrate species have been found to grow more rapidly in warmer environments.
What’s more, urban lighting attracts more insects. That means more food for urban-dwelling spiders. This increase in prey could lead to heavier, fatter and more fecund spiders. The fact that urbanization benefits spiders is a good thing, said Lowe.