Researchers have discovered that certain species of spiders consume tiny freshwater fish often twice its size, according to Reuters.

Scientists have known for some time now that spiders are able to consume fish, but recent studies showed the practice to be more common than previously believed.

"Fish may represent a 'big-ticket item' in the nutritional budget of semi-aquatic spiders," said zoologist Martin Nyffeler, of the University of Basel in Switzerland, who led the study, according to Reuters.

The researchers found that these groups of spiders can be found in every continent, except for Antarctica.

The study was published in the scientific journal PLOS ONE this week.

"Fish meat is high-quality prey regarding protein content and caloric value," Nyffeler said. "Feeding on fish may be particularly advantageous during the mating period when the elevated energy and protein requirements of gravid (pregnant) female spiders require increased food intake, or at times of limited availability of invertebrate prey."

Fish eating spiders use effective enzymes and neurotoxins in order to kill and digest fish. Some semi-aquatic spiders are capable of swimming and are even able to walk on surfaces of streams, ponds, swamps, and lakes.

Spiders usually anchor their hind legs on to a surface like a plant or stone and use their front legs to trap the prey on water surface. Once a fish gets trapped, it is then dragged to a dry place like a tree trunk or a rock and start eating their prey.

"The findings of such a large diversity of spiders engaging in fish predation is novel. Our evidence suggests that fish might be an occasional prey item of substantial nutritional importance", said Nyffeler in a statement.

It usually takes many hours for a spider to consume an entire fish until nothing but the bones and scales are left.

Researchers found around 18 species of spider from five families that are capable of eating fish.

Around 30 species of fish that ranged from an inch to 2-1/2 inches long (2 to 6 cm) were found trapped and consumed by spiders in the wild.

In North America, the spider species Dolomedes triton are repeatedly seen catching fish and the species Dolomedes facetus steals goldfish from ponds in suburban gardens in Australia.

"Spiders are more adept predators than most give credit for," said Brad Pusey of the University of Western Australia, who also worked on the study.

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