Even the Spiders Are Bigger in the City

A golden orb weaving spider in Brisbane, Australia Karora via Wikimedia Commons

Most animals don't tend to thrive in big cities, and you could be forgiven for thinking that this might be true for spiders, especially given that many people are not fond of them. But a new study found that certain types of spiders grow bigger and more fertile in urban areas, compared with the countryside—arachnophobia be damned.

A team of Australian researchers examined spiders living in a wide variety of spots around Sydney, and found that more densely populated areas hosted larger arachnids. Locations with more hard surfaces, like concrete, also were found to have spiders with bigger ovaries, a trait linked to higher fertility, scientists wrote in a study published Wednesday in the journal PLOS ONE.

The scientists also found that the species examined in the study, golden orb weaving spiders (Nephila plumipes), were larger in more affluent areas.

What's going on here—do spiders feed on the one percent or something?

Cities tend to be hotter than rural surroundings, a phenomenon known as the urban heat island effect, because hard surfaces like concrete absorb heat from the sun and hold onto it longer than vegetation. The researchers think this is one of the main reasons spiders are bigger in more developed areas; heat helps all a manner of insects and arachnids grow bigger. (One explanation for the saying, "Everything's bigger in Texas.")

There may also be more tasty insects to eat, like flies, that could be attracted to trash. Cities tend to have more nighttime light, which could also draw in insects, all the better to be snared and eaten by spiders.

Finally, spiders may be bigger in richer areas because these places tend to have better managed green spaces and parks, which could give rise to a wide variety and number of insects to eat, the scientists wrote.