There are at least 26 species of spiders who eat fish, a new survey finds, suggesting how this badass behavior is remarkably widespread: It’s witnessed on every continent except Antarctica.
The fish captured by these semi-aquatic spiders usually ranged between just 2 and 6 centimeters in length. But on average, these fish were 2.2 times longer than the spiders, not including the legs. The largest fish captured was 9 centimeters long and weighed 12 grams (a goldfish from Sydney).
It’s not that fish predation by spiders have never been observed before. But over three-fourths of the published reports on fish-eating spiders are about just two genera of spiders: Dolomedes and Nilus, which live in North America, Europe, New Zealand, and Australia. However, Martin Nyffeler from the University of Basel suspected that simply was not the case; a quick Google Image search showcases much, much more.
So, he and Bradley Pusey from the University of Western Australia reviewed observations of 89 incidences of fish predation by spiders at the fringes of shallow freshwater streams, rivers, lakes, ponds, swamps, and marshy fens. They discovered that spider species who fish can be found in at least eight families.
That includes spiders from five families observed catching fish in the wild: one species from Liocranidae, two from Ctenidae, over a dozen from Pisauridae, Trechaleidae, and Lycosidae. The list also includes spiders from three families who’ve been caught predating fish in the lab: Cybaeidae, Desidae, and Sparassidae. All in all, that’s at least 26 species of fish-eating spiders.
Some of these spiders can swim and dive, others can walk on the water. All of them have neurotoxins and enzymes that allow them to kill and digest fish. What usually happens is this: A spider will anchor its hind legs to a stone or a plant while its front four legs rest on the surface of the water. After it ambushes the fish, the meal is dragged to a dry place, where the subsequent feeding process can take up to several hours. Here are some examples from Neotropics:
Fish predation appears to be more common in warmer areas near the equator and in the mid-latitudes. That’s probably because warmer water holds less oxygen, forcing fish to spend more time at the surface where spiders wait, Nyffeler explains to Science. Half of the wild observations come from the US, and especially the wetlands of Florida, which are considered the “El dorados” for semi-aquatic spiders, he tells New Scientist.
Most of the spiders eat a variety of things: from insects and frogs to mice and bats. “Our evidence suggests that fish might be an occasional prey item of substantial nutritional importance,” Nyffeler says in a news release. They’re a “big ticket item,” seeing how the average fish targeted has up to 200 times the biomass of an insect.
The work was published in PLOS ONE this week. And for even more of these excellent pictures, be sure to check out all the figures in the paper. Below are more pictures from Australia, Asia, and Africa.
[University of Basel via Science, New Scientist]
Images: 2014 Nyffeler, Pusey
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