By Dr. Becker
If like many people, you’re a little frightened of spiders, you might want to make it a point to avoid cosmopolitan spiders in particular. Why? Because a new study reveals that certain city-dwelling spiders grow larger than their rural counterparts, and also produce more eight-legged baby spiders.1
The humped golden orb-weaving spider (Nephila plumipes) is native to the Australian countryside, but it also thrives in urban areas like Sydney, according to researchers at the University of Sydney. And not only are the spiders flourishing in cities, they’re growing larger than their country relatives and are also able to reproduce at a higher rate. (The researchers made that interesting discovery when they weighed the female spiders’ ovaries.)
Urban Exploiters: Suited for City Life
Study authors at the University of Sydney School of Biological Sciences have dubbed Nephila plumipes an “urban exploiter,” according to lead researcher Lizzy Lowe. In an email interview with Live Science, Lowe explained:
“The effects of urbanization on wildlife are very varied – some do well, others don’t. Animals which benefit from urbanization are called urban exploiters, and these species (including the spiders from this study) do better in urban areas than their natural habitats.”2
For the study, the researchers captured over 200 orb-weaving spiders from urban, semi-urban and semi-rural areas in and near Sydney. The city locations included parks, gardens, and patches of vegetation adjacent to houses and other buildings. The semi-rural areas where spiders were collected were less developed.
The researchers discovered that the city-dwelling spiders had longer tibias (leg segments) than the semi-rural spiders. (Tibias are used to determine the size of spiders.) The average tibia length for the country spiders was 0.37 inches, significantly shorter than the average tibia length of urban spiders at 0.48 inches. And some of the city critters were bigger still, with the largest tibia length measured at 0.55 inches.
In addition to their larger size, female urban orb-weaving spiders were found to have ovaries that accounted for up to 39 percent of their total body weight. In the world of spiders, big ovaries mean a higher reproductive capacity.
Hot Time in the City
The study authors believe these findings suggest that highly populated areas with lots of buildings and roads actually make excellent habitats for orb-weaving spiders. The explanation, according to Lowe, is simply that these spiders like the heat, and the concrete city landscape delivers an “urban island-heat effect.”
The good news for human city dwellers (even the squeamish ones) is that orb-weaving spiders find mosquitos and other pesky insects rather tasty, so they add value as a natural form of pest control!
And even better news is that the humped golden orb-weaver is shy around humans and rarely delivers a bite.