A new research conducted by Prof Martin Nyffeler from the University of Basel and Prof Bradley Pusey from the University of Western Australia provides evidence that fish predation by spiders is geographically widespread, occurring on all continents except Antarctica.
Example from Europe. Gravid adult female Dolomedes plantarius captured stickleback, Pungitius laevis, in turf pond in East Anglia, UK. Image credit: Helen Smith, South Lopham, Norfolk, UK.
The scientists analyzed more than 80 incidences of fish predation by five families of semi-aquatic spiders – Pisauridae (nursery web spiders), Ctenidae (wandering spiders), Trechaleidae (longlegged water spiders), Lycosidae (wolf spiders) and Liocranidae (spinylegged sac spiders).
These spiders, some of which are capable of swimming, diving and walking on the water surface, have powerful neurotoxins and enzymes that enable them to kill and digest fish. In most cases, they eat fish in combination with other prey, mostly insects.
“The finding of such a large diversity of spiders engaging in fish predation is novel,” said Prof Nyffeler, who is the first author of the paper published in the open-access journal PLoS ONE.
“Our evidence suggests that fish might be an occasional prey item of substantial nutritional importance.”
Examples from North America. A – Dolomedes triton caught mosquitofish in backyard pond near Tampa, Florida; B – Dolomedes triton feeding on fish, probably mosquitofish Gambusia holbrooki, in garden pond near Lady Lake, Florida; C – Dolomedes triton feeding on small fish on Tsala Apopka Lake, Florida; D – Dolomedes triton feeding on fish in garden pond near Lady Lake, Florida; E – Dolomedes triton devouring fish on edge of small, slow-moving stream near Fayetteville, North Carolina; F – Dolomedes okefinokensis feeding on small fish in swamp in Big Cypress National Preserve, Florida. Credit: Stacy Cyrus / Machele White / Claire Sunquist-Blunden / Patrick Randall / Misti Little.
Most incidences have been documented in North America, especially in the wetlands of Florida, where semi-aquatic spiders have often been seen catching and eating small freshwater fish such as mosquitofish.
Vision plays a relatively minor role in prey detection and while some spiders rely on feeling ripples in the water made by their prey, most rely on the dorsal fin of a fish touching their outstretched legs.
Some spiders anchor their hind legs to a stone or plant with their front legs resting on the surface of the water, ready to sense and ambush their fishy dinner.
While spiders usually feed on prey items that are smaller than themselves, some semi-aquatic spiders capture fish with bodies on average 2.2 times as long as the spiders. And some spiders catch fish which are 4.5 times their weight.
Examples from South America. A – Trechalea sp. eating characiform while sitting on a rock in middle of small river near Paratebueno, Cundinamarca, Colombia; B – Trechalea sp. pulling characiform on stone on edge of shallow, small stream near Quebrada Valencia, Magdalena, Colombia; C – Trechalea sp. devouring characiform while sitting on tree trunk on edge of Rio Frijoles, Central Panama; D – Trechalea sp. eating characiform on bank of Rio Maicuru, Pará State, Brazil; E – Trechalea sp. eating characiform while sitting on rock in middle of small river near Paratebueno, Cundinamarca, Colombia. Credit: Solimary Garcia Hernandez / Juan Esteban Arias A. / Jessica Stapley / Jacques Jangoux.
Fishing spiders possess large strong mouthparts capable of piercing their preys’ skin. Most fish are bitten by the spiders at the base of the head. Once a spider catches its fish, it always drags it to a dry place before eating it. This is because the spider has to pump enzymes into its prey before it can be digested, and also because there is less chance of the fish getting away.
It takes a spider many hours to consume a fish and the extra nutrients and calories in a fish – compared to an insect – may give the spider an advantage during the mating period.
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Nyffeler M, Pusey BJ. 2014. Fish Predation by Semi-Aquatic Spiders: A Global Pattern. PLoS ONE 9 (6): e99459; doi: 10.1371/journal.pone.0099459
