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Along Came a Spider and Sat Down to Fish

A large range of spiders can catch and eat fish that are several times bigger and heavier than them, according to a report in PLOS One.

Prof Bradley Pusey of The University of Western Australia has described almost 90 incidences of fish predation by five families of semi-aquatic spiders found at the fringes of shallow freshwater streams, rivers, lakes, ponds and swamps, mostly in warmer places. Fish predation is geographically widespread, occurring on all continents except Antarctica. In most cases, the spiders eat fish in combination with other prey, mostly insects.

Vision plays a relatively minor role in prey detection. While some spiders feel ripples in the water made by their prey, most rely on the dorsal fin of a fish touching their outstretched legs. Some spiders will lay in wait, anchoring their hind legs to a stone or plant with their front legs resting on the surface of the water.

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 and 4.5 times their weight.

Fishing spiders have large, strong mouthparts that pierce the skin of their prey. They have powerful venoms that contain hundreds of different neurotoxins, some of which are specific to vertebrate nervous systems. Most fish are bitten by the spiders at the base of the head. Death can be sudden or can take almost an hour.

Once a spider catches its fish it drags it to a dry place and pumps enzymes into it to enable digestion, which can take many hours.

Pusey says that fish have more nutrients and calories than insect prey, and this may give the spider an advantage during the mating period.