Scientists find fish-eating spiders around the world

Spiders are pretty well known as good hunters, feeding mainly on other insects. But new research is showing just how many of them are good at catching — and dining on — fish as well.

The study in the journal PLOS ONE by zoologist and spider expert Martin Nyffeler, from the University of Basel in Switzerland, and Bradley Pusey, from the University of Western Australia, documents more than 80 incidents of spiders killing fish across the world, confirming that spiders do not exclusively eat insects.

At least 18 different spider species have been observed catching fish in the wild, according to the study.

"The finding of such a large diversity of spiders engaging in fish predation is novel," Nyffeler said.

Most of these fish-killing spiders are semi-aquatic, with the ability to swim, dive and walk on the water's surface. These spiders are equipped with powerful neurotoxins and enzymes that help them kill and digest fish that can be two times their size.

To catch their prey, spiders would wait near the surface of the water on the edge of a stream with their hind legs anchored on a stone or plant and pierce the skin of the fish as it swam by with a venomous bite. The spider would then drag the fish to a dry place to begin the feeding process, which could take several hours.

"(The spiders) have evolved very potent neurotoxins (for) killing fish within seconds to minutes," Nyffeler told USA TODAY in an e-mail. "They are well-adapted for a life near and in the water."

The catches take place in every continent except Antarctica, and most occur in warmer climates. North America has the most documented incidents, especially in the Florida wetlands. Nyffeler hypothesizes that water contains lower oxygen levels at warmer temperatures, causing more fish to come to the surface to breathe and feed. This makes fish more likely to be caught by spiders who operate on the water surface.

The fish caught by spiders were all freshwater fish ranging from less than 1 inch to 2 inches long, Nyffeler said. They were among the most common fish species in their respective geographic areas, including the mosquitofish in southeastern U.S. and the killifish in Central and West Africa.

Some spiders occasionally catch other small vertebrates including frogs, toads, salamanders, lizards, snakes, mice, rats, bats and birds, Nyffeler said.

Spiders who only prey on fish are very rare and most likely restricted to areas where spiders have easy access to small fish, such as in artificial rearing ponds or small, shallow water bodies, according to Nyffeler.

Researchers still don't know the full extent of the nutritional value of fish, but it is most likely "high quality prey," Nyffeler said. The researchers hope to conduct a new study expanding on their findings.

"One of the purposes of this study was to stir up the interest among scientists for these very interesting semi-aquatic animals," Nyffeler said.