(Image: Patrick Randall, Fort Bragg, North Carolina)

All the fish notices are two innocent-looking hairs draped from a leaf on the surface. Then in a twinkling of an eye, a shadow descends. They were not hairs, but the front legs of a spider. The fish is quickly paralysed by neurotoxins, snatched from the water and dragged away to meet its doom – by a spider less than half its length and a quarter its weight. The spider will spend hours munching on its prey, leaving nothing but bone and scales.

This is the most common ploy spiders adopt to catch and eat fish, according to the first global survey of pescatarian spiders. The study reveals that many more spiders are piscivores than previously thought, and they tuck in on every continent except Antarctica.

We have known for a while that semi-aquatic “fishing” spiders called pisaurids eat fish, mostly species from the genera Dolomedes and Nilus. They can swim, dive and walk on water.


The new survey expands the list greatly, recording reported cases of spiders eating fish. The trawl identified 26 fish-eating species: 18 observed dining on fish in the wild, and the rest in captivity.

What about chips?

“It encompasses at least eight spider families, five observed eating fish in nature and another three seen only in captivity so far,” says Martin Nyffeler of the University of Basel in Switzerland.

Half the wild observations came from the US, especially Florida, where the six spotted fishing spider (Dolomedes triton) (see above) is known to feast on mosquitofish in the Everglades. “These wetlands in Florida are ‘El dorados’ for semi-aquatic Dolomedes spiders,” says Nyffeler.

Other reports came from wetlands in the UK, where the great raft spider (Dolomedes plantarius) sometimes catches small fish like sticklebacks, in swamps in South America and garden ponds in Australia. The largest fish the spider caught was a goldfish 9 centimetres long, from a pond in Sydney.

It’s unlikely that any spiders survive exclusively on fish, says Nyffeler. Instead, fish are probably a fortuitous “big ticket item” that allows them to pig out, possibly prior to mating. The average fish targeted has up to 200 times the biomass of an insect, and much of that is protein-rich muscle. Nevertheless, all five fish-eating families get most of their food from insects and other arthropods.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0099459