{"id":49908,"date":"2022-10-17T01:00:48","date_gmt":"2022-10-17T05:00:48","guid":{"rendered":"https:\/\/www.thenatureofcities.com\/?p=49908"},"modified":"2022-10-14T19:55:39","modified_gmt":"2022-10-14T23:55:39","slug":"urban-spiders-fuzzy-friends-or-fearsome-foes","status":"publish","type":"post","link":"https:\/\/www.thenatureofcities.com\/TNOC\/2022\/10\/17\/urban-spiders-fuzzy-friends-or-fearsome-foes\/","title":{"rendered":"Urban Spiders \u2013 Fuzzy Friends or Fearsome Foes?"},"content":{"rendered":"
We know a lot more about how urbanization generally affects spider communities outdoors. Interestingly, in a meta-analysis of lots of arthropod studies across urbanization gradients, spiders were the only taxa that were not clearly and negatively affected by urbanization.<\/blockquote><\/figure>\n

Spiders are among my favorite urban neighbors. They\u2019re flashy, charismatic, and they\u2019re everywhere. Spiders also evoke a range of emotions and thoughts from their human cohabitants. If you see one in your house do you squish it? Do you capture it gently and relocate it? Do you run away screaming? Do you get excited and acquainted with one another?<\/p>\n

One week in 2020 I was making coffee early in the morning and noticed a small little spider on the wall of the kitchen next to me. I thought it was pretty cool looking but didn\u2019t think much of it and went on with my day. The next morning, I came down, and there it was again! I watched in interest as it hopped around and stared at me. And then the next morning it was back. That\u2019s when I took a photo and later discovered through iNaturalist<\/a> that it was Adanson\u2019s house jumper (Hasarius adansoni<\/em>). It stayed around for a few more days, watching me make coffee. And then it disappeared.<\/p>\n

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Adanson\u2019s house jumper (Hasarius adansoni) took residence in the author\u2019s kitchen (Lamma Island, Hong Kong)<\/figcaption><\/figure>\n

Interestingly, today a paper came out showing that spiders exhibit patterns of REM sleep\u2026 spiders dream! I now wonder if my companion had a particularly rough week of sleepless nights and joined me early after sunrise also badly wanting some caffeine.<\/p>\n

This week I\u2019ve enjoyed a rather large huntsman spider in the shower. When I turned the water on the spider ran around and I figured it was a goner. But I should not have underestimated the spider. It too stuck around for a few days\u2026 and my wife was not happy about it, nor the fact that I refused to move it.<\/p>\n

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A huntsman\u2019s spider (Heteropoda venatoria) in the author\u2019s bathtub (Lamma Island, Hong Kong)\u2026 and two contrasting opinions about this development. [the author also failed to take out the trash that morning]<\/figcaption><\/figure>While I\u2019m not afraid of spiders now, I was scared to death of black widows as a kid growing up in Los Angeles. Seriously, it was like rattlesnakes, sharks, and black widow spiders. While black widow spider bites can be painful and problematic they are very very rarely fatal \u2013 between 2000 and 2008 there were over 23,000 reported bites in the US<\/a> with 33.5% reporting \u201cmoderate effects\u201d, 1.4% \u201cmajor effects\u201d and no deaths. So, my fear was certainly not justified [probably don\u2019t need to be afraid of sharks either but that\u2019s another story]. Not surprisingly, depictions of spiders in the media<\/a> are part of the problem in generating such fear.<\/p>\n

Indoor diversity of urban spiders<\/strong><\/p>\n

There are a number of fun studies that have examined the question of indoor spider diversity in more detail. Entomologists \u201craided\u201d 50 homes in North Carolina in 2012<\/a> and collected all the arthropods they could. Spiders made up about 20% of the arthropod fauna in the homes on average and they found all sorts of spider types including funnel weavers, ghost spiders (scary), orb weavers, sac spiders, ground spiders, dwarf spiders, wolf spiders, wall spiders, goblin spiders, cellar spiders, jumping spiders, spitting spiders, cobweb spiders, and crab spiders.<\/p>\n

Other than entertaining (or frightening) their human cohabitants, what are the spiders doing? While drinking my coffee and watching my friendly H. adansoni<\/em> I liked to thank them for keeping mosquito populations low. But do they actually do this? Researchers have tested<\/a> this in salticid spiders (related to H. adansoni <\/em>in fact) in arenas with mosquitoes and found that spiders can consume between 2 to 9 mosquitoes a day! Female spiders also fed on a greater number than males.<\/p>\n

In truth, there is a lot we don\u2019t know about spiders and biodiversity in our homes. But there is increasing interest<\/a> in indoor biodiversity and ecosystem function relationships. I\u2019m willing to bet that spiders are key to a lot of indoor food webs.<\/p>\n

Urbanization impacts on spider diversity<\/strong><\/p>\n

We know a lot more about how urbanization generally affects spider communities outdoors. Interestingly, in a meta-analysis<\/a> of lots of arthropod studies across urbanization gradients, spiders were the only taxa that were not clearly and negatively affected by urbanization. This is likely a consequence of habitat- and species-specific responses in spiders that lead to either negative or positive effects on spider diversity.<\/p>\n

For example, in C\u00f3rdoba, Argentina, researchers found<\/a> that spider diversity was lower in urban sites relative to both suburban and exurban (non-urban) sites. On the other hand, for ground-dwelling spiders in Hungary, diversity tends to be higher in urban areas<\/a> relative to rural and suburban sites. In Sydney, spider diversity was highest in remnant habitat patches but gardens were also quite high in diversity. So, patterns of spider diversity across urban gradients are rather complex.<\/p>\n

Has urbanization caused any extinctions of spiders? This question is surprisingly difficult to answer for most arthropods. After all, if a species isn\u2019t in a city how do you know whether it has become extinct or was simply never there? For one case, scientists have found evidence<\/a> that the trapdoor spider Apomastus<\/em> has become extirpated in parts of the Los Angeles basin, leading to reduced genetic diversity.<\/p>\n

Despite the uncertainties and questions regarding urbanization effects on spiders, experts agree that urbanization is among the greatest threats<\/a> to spider conservation along with agriculture, climate change, and pollution.<\/p>\n

Behavior of urban spiders<\/strong><\/p>\n

Porchy (Nephila pilipes<\/em>) was a golden orb weaver spider that lived on my porch in 2017. She grew to be quite large, about the size of an orange from foot tip to foot tip. For months my wife and I watched daily as she would munch on flies, moths, and other creatures that would come into her web. Sometimes I would forget about her presence and ruin her web in the morning. No matter, she would rebuild it quite quickly and soon get back to work. N. pilipes <\/em>are particularly feared in Hong Kong by morning runners and hikers as their webs are frequently run into and the image of an orange-sized spider close-by is not comforting to some. But they\u2019re mostly harmless. [They will catch the occasional bat<\/a> or bird though!]\n

Anecdotally, it sure appeared that Porchy was leveraging our strong porch light to catch insects attracted to the bulb. The web was often positioned to exploit the light (or so it seemed) and she had good success during her time on the porch. And indeed, there are studies showing that spiders are attracted to light on buildings<\/a>. But the story is not as simple as it might seem\u2026<\/p>\n

Minnie Yuen was an undergraduate in my lab in 2016 whose passion for golden orb weaver spiders led her to conduct an experiment. She went to several sites in Hong Kong, found spiders, and then did an experiment where she set up a light at several webs and compared to unlit webs. She then put up video cameras at the webs to see how effective they were in catching insect prey\/moths. We were expecting to find that the spiders next to lights would catch more prey. And then, we found the opposite! Fewer prey were intercepted in the spiders\u2019 webs\u2026 but there were roughly equal numbers of moths that approached the web. We suspect that the light may have given moths an opportunity to detect the webs and avoid capture.<\/p>\n

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Porchy (Nephila pilipes) lived on the author\u2019s porch in 2017 and remains his favorite spider cohabitant in recent memory.<\/figcaption><\/figure>\n