Fish-Eating Aquatic Spiders: They’re Real, Sleep Well

It’s easy to view spiders as the creatures of nightmares. They’re amazing predators, they drink blood and the majority of them use webs or venom or incapacitate their victims. Still, water has always been considered one of their weaknesses.

A new study in the journal PLOS ONE by Martin Nyffeler, a spider expert from the University of Basel in Switzerland, and Bradley Pusey from the University of Western Australia, documents several species of spiders that can be classified as semi-aquatic.

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

Fish-eating spiders have the ability to swim, dive or even walk on the surface of water. They are also equipped with powerful neurotoxins and enzymes that allow them to quickly kill fish so that they can not only drink the blood, but consume the flesh as well. Most of the fish caught by spiders are almost twice as long as they are.

Nyffeler wrote to USA Today, “(The spiders) have evolved very potent neurotoxins (for) killing fish within seconds to minutes. They are well-adapted for a life near and in the water.”

Fish-eating spiders do not use webs to catch their prey. In order to catch fish, spiders wait near the water’s surface with their hind legs anchored on whatever is available and then they pierce the skin of their prey as it swims by. The spiders then drag their fish to a dry area to feed, taking several hours for the grisly task.

There are several species that have been noted to participate in fish-eating habits. Collectively referred to as “fishing spiders” in the study, those species are nursery web spiders, wandering spiders, longlegged water spiders, wolf spiders and spinylegged sac spiders.

Every continent aside from Antarctica showed evidence of these semi-aquatic spiders; almost always in warmer climates. The reason for this could be that the water contains lower oxygen levels at warmer temperatures. With less oxygen in the water, fish need to swim closer to the surface to breathe, putting them in reach of the spiders.

According to the study, North America, specifically Florida, has the most fish-eating spiders, and all fish-eating by spiders is said to take place in bodies of freshwater.

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

Spiders are not the only ones with a taste for sushi. Other insects credited with having fish in their diets include water scorpions, giant water-bugs, backswimmers, diving beetles and scavenger water beetles.

[ Image courtesy of National Geographic ]