The Urban Heat Island Effect is Triggering Larger and More Spiders

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Just when you thought Mother Nature couldn’t get any weirder, mankind has found a way to inadvertently make some spiders even bigger (and freakier) than they were before.

That’s right, people- we’re talking about big spiders. Now, before you go flying away to somewhere cold and uninhabited by eight legged monstrosities, hear me out. There’s actually a science behind why some species of spiders grow larger in urban areas than they do in natural settings.

This effect is called the urban heat island effect. This means that urban areas covered in concrete and people are warmer than neighboring natural landscapes full of trees and grasslands. This warmer zone combines with an increase in insect life, partially because of the lights that are used in urban settings. These lights attract more insects that spiders like to eat providing them with a cozy living environment, a consistent supply of food, and lots of corners in which to build their webs.

Variation in spider size. Photo: Elizabeth Lowe
Variation in spider size. Photo: Elizabeth Lowe

Recent studies on massive arachnids have focused on Nephola plimipes, or a type of orb-weaving spider commonly associated with massive webs that cover trees like a canopy in some areas of Australia. Elizabeth Lowe and researchers at the University of Sydney have studied these spiders in urban and rural settings to see how the urban heat island effect specifically affects how these spiders function.

Their research found that the spiders in urban areas were bigger, had a higher concentration of body fat, and were able to carry more spider babies than the spiders that lived in natural settings. While this particular study focused only on one species of spider, other research has been conducted on a variety of species that shows similar results to Lowe’s study.

Graph showing the rise in size of spiders and ovary weight. From Lowe EC, Wilder SM, and Hochuli DF (2014)
Graph showing the rise in size of spiders and ovary weight. From Lowe EC, Wilder SM, and Hochuli DF (2014)

Urbanization is harmful to some animal species like wolves, bears, foxes and coyotes that are often displaced by the increased suburban range of many cities. Their traditional hunting and living grounds are now taken up by housing complexes and shopping malls, forcing them into smaller and smaller natural areas while increasing the amount of human interaction they may face on a regular basis.

However, for other species like spiders urbanization has proven to be beneficial. Urbanization provides warm, hospitable environments to some spider species (like the orb weaver) and has proven to be beneficial to their growth and life cycle. Good news for the spider, bad news for the arachnophobe.

Reference:

Lowe, E. C., Wilder, S. M., & Hochuli, D. F. (2014). Urbanisation at Multiple Scales Is Associated with Larger Size and Higher Fecundity of an Orb-Weaving Spider. doi: 10.1371/journal.pone.0105480.g002

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