Great news for people who perform LeBron-class vertical leaps when they see a spider: The unnatural environment of cities seems to be inflating these creatures like bulging eight-legged balloons, according to new research.
Of course the focus of today's study in PLOS ONE is already a giant, nightmarish ball of eyes, legs, and fangs: Nephila plumipes, an orb-weaving spider whose massive colonies can cover the sky with webs the size of circus nets. Elizabeth Lowe and her colleagues at the University of Sydney have been monitoring the species around the city as well as the 'burbs, and they've noticed a stark difference in the urban spiders: Compared to their bushland-dwelling cousins, they are bigger, pack on more body fat, and have heavier ovaries. That last finding suggests these guys are great at having tons of spider babies.
Lowe got in touch to explain how she entered the world of these swollen spiders. "I'm interested in the way that living in cities affects wildlife," she says. "Spiders are a great taxa for this because they are very diverse and some of them do particularly well in cities." (Lowe isn't the first to probe the link between cities and arachnid physiology; for instance, a 2013 study found that certain species thrive in vacant lots converted to urban gardens.)
Lowe believes two things about cities are influencing these critters' bulk: temperature and an abundance of insects to eat. "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," she says. "Higher temperature is associated with increased growth and size in invertebrates."
As for the endless buffet of nourishment, the spiders can thank the light beaming from Sydney's street lamps, office buildings, and parking lots. "Urban lighting also may be a contributing factor as it attracts insects and means more food for spiders in those environments," Lowe says. "This increase in prey would result in bigger, heavier, more fecund spiders."
While Lowe's research was confined to orb weavers, it's a good bet that more spiders are exploiting the advantages of cities, too. As her study asserts: "Other web-weaving spiders are also known to thrive in urban environments and it is likely they are responding to similar modifications to the natural environment."