Researchers from the University of Basel, Switzerland and the University of Western Australia discovered that spiders around the world occasionally prey on small fish.

These spiders are called semi-aquatic spiders, and typically thrive in shallow waters, such as the banks of ponds, streams, rivers and swamps. 

Martyn Nyfeller, lead author of the study from the University of Basel, and his colleagues examined five families of spiders that were documented to have consumed small fish in the wild. Researchers found that at least three families of spiders contained in the laboratory were seen capturing and consuming fish.

The researchers found that some of these spiders had the ability to swim, dive, and walk on the surface of the water in order to catch their prey. Although they were relatively small, these spiders were endowed with large amounts of neurotoxins that enabled them able to paralyze their prey.

The spider first anchored its hind legs to a stable platform such as a plant or stone to catch the fish. Its front legs rested quietly on the surface of the water. Once the fish swam by, the spider pounced onto it and dragged it to a dry place.

"The finding 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,"  Nyffeler said.

The study also stated that these spiders were seen on all the continents except Antarctica. Most of the documented incidents of spiders catching fish to supplement their diet came from North America, particularly in Florida's wetlands. Spiders observed in Florida preyed upon small fish such as mosquito fish.

Further details of the study were published in the June 17 issue of PLOS ONE.