Spiders get bigger in the big city

Bad news for city-dwelling arachnophobes: Some spiders may be bigger in your neck of the woods. Or at least one species of arachnid appears to be. Golden orb-weaving spiders living in the most urban parts of Sydney, Australia, tend to be bigger than those found in surrounding rural areas, according to a study published August 20 in PLOS ONE.

The golden orb-weaving spider (Nephila plumipes) is a yellow-brown web-building species found in Queensland, Australia, as well as Indonesia and some islands in the Pacific. Though its large size would probably be scary to some, I’d place this spider in the “don’t worry too much about it” category of Australian arachnids. It doesn’t like to bite people, even if that bite is painful. (In contrast, the bite of a Sydney funnel-web spider is deadly, and those spiders will attack a human.)

From April to June 2012, Elizabeth Lowe and colleagues at the University of Sydney collected golden orb-weaving spiders from sites across the Sydney area, including the city center, near the fabulous Manly Beach, inside the beautiful Royal Botanic Gardens and north of the city in the more rural Ku-ring-gai. They measured the spiders for size, weight and other morphological traits. The researchers also took note of the characteristics of the local landscape and the microhabitat in which the spiders lived.

Microhabitat was likely to be important, Lowe’s team figured, because these spiders are sedentary. They build semi-permanent webs and hang out in that one spot for their entire mature lives.

The researchers compared the spiders by size and location. When they looked at broad categories such as “park” or “bushland,” they found no predictors of spider size or condition. But when they started including more details about the spiders’ habitats, trends showed up. Arachnids living in the city center and those found closer to the coast, for example, were “significantly larger,” Lowe and colleagues found. And it seemed that, like humans, spiders got a benefit from living in richer suburbs — they were in better condition.

When the researchers examined characteristics of the spiders’ microhabitats, they found additional trends. Spiders got bigger when there were more hard surfaces and less vegetation around. Condition improved and ovary size got bigger in areas with less leaf litter.

“Our study shows that [the golden orb-weaving spider] is an urban exploiter,” the researchers conclude. Like people, it appears, some of them just do better in the big city.