New Evidence Pegs Semi-Aquatic Spiders As Fish-Eating Predators
June 19, 2014

New Evidence Pegs Semi-Aquatic Spiders As Fish-Eating Predators

Gerard LeBlond for - Your Universe Online

A new study, published in the academic journal PLOS ONE, from zoologists in Switzerland and Australia, state that spiders all over the world not only prey on insects, but also feed on fish.

Ecologists view spiders as an insect predator, but research has revealed that certain larger species of spiders will occasionally catch and consume small fish.

Martin Nyffeler from the University of Basel, Switzerland and Bradley Pusey from the University of Western Australia gathered and documented reports of spiders preying on fish from around the world.

The study revealed that as many as five families of spiders have been observed catching and feeding on small fish in the wild and three other families have caught and consumed fish in a laboratory setting. The spiders are semi-aquatic species that normally inhabit the edges of shallow freshwater ponds, swamps and streams. Some of the spiders can also float on the surface, as well as swim and dive.

The neurotoxins and enzymes produced by these spiders are powerful enough to immobilize and consume fish larger than its size and weight.

“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,” says Nyffeler.

According to the study, this predatory action with certain spider species has been reported from all continents, except Antarctica. The wetlands of Florida, United States have the most reported incidents of spiders catching and consuming small fish, like the mosquitofish.

Typically the spider will anchor its hind legs to a solid object such as a stone, branch or plant and rest its front legs on the surface of the water to catch its prey. Once the spider has immobilized the fish, it will drag it to dry land and consume it. The process can take several hours to complete.

The incidents occur mostly in warmer climates such as the Florida wetlands. Some species of spiders may occasionally prey on frogs, toads, salamanders, lizards, snakes, mice, rats, bats and birds, as well as small fish the study revealed. Previous studies on fish eating spiders have been published before, but from only a few locations; this study covered a broader range.

North America had the most incidents with 45 from the United States, which equaled 51 percent of the total reported occurrences around the world. Most of them were in the southeast, mainly Florida; eight occurred in California; and one each in Arizona, Michigan and Wisconsin. There was also one occurrence on a dock at Shoe Lake, Ontario, Canada.

There were 14 incidences that occurred in Brazil, Colombia, Costa Rica, Panama, Peru and Ecuador. Australia had twelve reports of fish-eating spiders, while less occurrences were in Asia with seven and Africa with six. Europe reported four from the United Kingdom, Italy and France.

The genus Dolomedes was the most common group of fish-eating spiders. This group has worldwide distribution and although some are nocturnal, they all can swim, dive and walk on the surface of the water. The genus contains more than 90 different species of spiders. It has been suggested that the real number of incidents of fish-eating spider occurrences is much higher than the study has revealed.

Image 2 (below): Fishing spider Dolomedes facetus captured fish (genus Xiphophorus) in garden pond near Brisbane, Queensland, Australia. Credit: Photo by Peter Liley, Moffat Beach, Queensland