Elizabeth Lowe, via New Scientist.

We all know that urbanization can have detrimental consequences on animals. Destroying habitats and replacing them with concrete jungles to suit our ever burgeoning population usually results in a loss of biodiversity as species fail to adapt to their new urban lifestyle. Now, it turns out that the situation is even more dire than we could have ever imagined- it’s making spiders bigger. *Shudder*

Urbanization significantly alters landscapes, impacting the local climate and dramatically changing natural animal habitats. Many species are unable to exploit these novel environments and consequently populations experience decline, but some seem to be able to thrive in them. One particular species that caught the eye of University of Sydney researcher Elizabeth Lowe was the golden orb-weaver spider (Nephila plumipes). While these spiders are common in the Asia Pacific region, Lowe started to notice that they were looking unusually plump. She therefore wondered whether this could be linked to urbanization and decided to investigate.

Lowe and colleagues collected a total of 222 female spiders from various study sites in Sydney, ranging from inner-city areas to continuous bush land. They wanted to see if urbanization affected the growth and reproduction of these spiders, so they measured the size, fat reserves and egg production of the specimens gathered.

They discovered that more built-up areas that were further from bush land tended to house larger spiders. Specimens removed from inner-city parks on average weighed 1.6 grams. That may not sound like much, but when compared to spiders taken from bush land areas that weighed just 0.5 grams on average, it’s easy to see that they are unusually chubby. Furthermore, spider ovaries were also significantly bigger in urban sample sites and in areas with more hard surfaces and less leaf litter.

The researchers propose that two factors are likely contributing these observed changes: increased temperature and prey availability. Urban areas are often significantly warmer than surrounding rural areas due to hard surfaces and lack of vegetation, which is called the urban heat island effect. It is known that temperature can significantly affect the growth and size of spiders, therefore it is likely that the higher temperatures experienced in more urban areas are encouraging spider growth. It is also possible that there is more prey available to the spiders in urban areas, which could also explain the increase in growth observed.  

Interestingly, they also found that large spiders were associated with artificial light structures such as light posts. Bugs are attracted to artificial lighting, therefore it’s likely that the spiders are able to catch more prey in these lit up areas.

One final, slightly bizarre observation was that wealthier areas generally had larger spiders. The researchers are uncertain as to why this might be, but they propose that wealthier areas might have more hard surfaces and thus are warmer.

While the researchers only looked at the Sydney area, they believe it’s probably happening all over the world. I’m sure the thought of even bigger spiders is sending shivers down the spines of many readers right now, but we have to remember that while they might look disgusting, spiders do lots of good - they eat lots of nasty bugs like mosquitoes. Perhaps we should be embracing these larger spiders?

[Via New Scientist and PLOS ONE]

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