Fish-eating spiders 'widespread'

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Ancylometes spiderImage source, Other
Image caption,
The fish were often much bigger than the spiders that caught them

Scientists have discovered that a number of spider species catch and eat fish.

Spiders are traditionally viewed as predators of insects, but a new study suggests that eating fish is widespread among species that live near water.

In some cases, the arachnids used powerful poisons to kill fish that were much bigger than them.

Details of the study by a Swiss-Australian team appear in the academic journal Plos One.

Martin Nyffeler from the University of Basel in Switzerland and Bradley Pusey from the University of Western Australia gathered and documented numerous incidents of spiders catching fish.

Their review of the evidence shows that spiders from as many as five families have been observed eating small fish in the wild and three more families contain species that catch fish under laboratory conditions.

These semi-aquatic spiders typically dwell at the fringes of shallow freshwater streams, ponds or swamps.

Some are capable of swimming, diving and walking on the water surface. But they generally have powerful neurotoxins and enzymes enabling them to kill and digest fish that are bigger and heavier than them.

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Image caption,
Fish might be occasional prey for spiders that dwell near water

Fish caught by the spiders were, on average, about twice as long as their arachnid predators.

"Our evidence suggests that fish might be an occasional prey item of substantial nutritional importance," said Dr Nyffeler.

Fish eating by spiders has been reported from all continents with the exception of Antarctica. Most incidents have been documented in North America, especially in the wetlands of Florida.

Here, semi-aquatic spiders have often been witnessed catching and eating small freshwater fish such as mosquitofish.

In order to catch its prey, the spider will typically anchor its hind legs to a stone or a plant, with its front legs resting on the surface of the water, ready to ambush.

The fish is then dragged to a dry place before the feeding process can begin. This usually lasts several hours.