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ECOVIEWS: Some spiders prey on mammals

Whit Gibbons

Whit Gibbons

When I saw the gigantic spider carrying a small deer across the forest floor, I became alarmed. My fear abated when I read the caption under the photograph I was looking at. To paraphrase, by changing the scientific names: “A (western desert tarantula) preying on a (kangaroo rat) in Tucson, Arizona.” Had I not been so taken by the idea of its being a deer, I would have noticed the prey’s long tail. A spider carrying a full-grown mouse is impressive.

I knew I was in for a treat when I received the scientific paper by Martin Nyffeler and Richard S. Vetter with “spiders feeding on mammals” in the title. Nyffeler (University of Basel, Switzerland) and Vetter (University of California, Riverside) published the paper in the Journal of Arachnology (the study of spiders and scorpions). Their compilation of records of spiders capturing, killing and eating wild mammals in natural settings reveals how truly extraordinary these eight-legged creatures are.

One-third of the spider predations on wild-caught mammals were confirmed to be on what most of us view as pests: house mice and rats. Most of the rest were also rodents, and most of those are presumed to have been house mice. Spiders demonstrated their open-mindedness and impartiality by eating other mammals, including shrews, voles and even a small primate from Madagascar. More than a dozen kinds of spiders representing at least seven different families were implicated as small mammal slayers. The fact that spider predation on mammals was documented in seven countries on six continents suggests that lots of mice and rats around the world need to avoid getting tangled in a web while simultaneously looking over their shoulder for a living nightmare in pursuit. The authors conclude that the success of some spiders “in subduing small mammals can be explained by their ability to spin strong webs made up of tough silk and producing a very potent toxin …specifically targeting the vertebrate nervous system.”

Almost all spiders have venom, though a few do not. Most spiders are too small to bite people or just don’t care to. In addition to mammals, spiders have been known to ensnare and consume lizards, snakes, bats, birds and even fish. A spider is not to be trifled with. An upside about spiders from the human standpoint is that none gets bigger than a human hand. Imagine if some reached the size of dogs. The photos in books of spiders carrying mammals would indeed be terrifying and might include a few not-so-small primates.

Spiders are wondrous creatures with amazing abilities. Yet many people do not welcome them. Some people have an irrational fear of spiders (arachnophobia). Some do not even want to see a picture of a spider. A few years ago, I recounted my experience in overcoming my own trepidation. I turned over a rock during a field trip out West, and an enormous, black, furry tarantula crept out. My companion encouraged me to pick it up. Being of an age to accept such a challenge, I let the monster crawl onto my hand and stood breathlessly as it moved up my arm to my shoulder. I retrieved it with my other hand. I have not been afraid of spiders since, neither small nor large. I continue to be intrigued with each one I find.

I don’t know why anyone would want to get rid of a spider living outdoors. Watch them carefully and you will discover a fascinating group of animals living in your neighborhood. I recently ran across another paper by Nyffeler titled “The southern black widow spider …as a predator of the red imported fire ant.” You may not like spiders but when you consider them on their merits, such as their ability to eat fire ants and unwelcome rodents, you might learn to appreciate them. And I have told you how to lose your fear of them.