While studying the ways animals adapt to city life, ecologist Lizzy Lowe discovered golden orb weaving spiders thrive in Sydney's concrete jungle.

''They seem to really enjoy living by the coast,'' Ms Lowe, from the University of Sydney, said.

The more urbanised and wealthier the suburb, the fatter the golden orbs found in nearby gardens and pockets of bushland, she said.

''They're still building their webs in trees but they don't like the vegetation to be too dense. They like big open areas.''

The heftiest spiders were residents of the Botanic Gardens and Tamarama, while arachnids collected from rural sites such as the Brisbane Waters National Park, near Gosford, were considerably leaner.

Females in the city also had larger ovaries, which meant they were either hosting larger eggs or more of them, and had a better chance of producing healthy offspring.

''That's one reason why we think they might be in such high numbers in urban areas,'' said Ms Lowe, whose findings have been published in the science journal PLOS ONE.

Ms Lowe said the man-made habitat of cities offered golden orb weavers several advantages over country living.

Urban areas with lots of concrete and steel structures retained heat better than vegetation, a phenomenon known as the urban heat island effect, which could raise the nearby ambient temperature by up to three degrees.

''We think by being in these areas with higher temperatures the spiders have more energy to put towards reproduction and they're surviving longer as well,'' Ms Lowe said.

Compared with rural areas with high density vegetation, the city also provided spiders some protection from predators such as birds, while offering them a good range of insects to eat.

Ms Lowe suspected the artificial lights in cities that attract more insects give Sydney spiders an edge.

While Ms Lowe's study did not uncover why spiders were fattest in well-heeled locations, she said wealthier suburbs often spent more money on conservation and land management, which may suggest those ecosystems were healthier and better spider habitat.

Far from being a creature to fear, Ms Lowe said it was a good thing golden orbs prefer city living because they control pest species like flies and mosquitoes and manage the populations of plant-eating insects. They are also an important source of food for birds.

''They're an essential link in the food chain,'' she said.