Scientists have identified a group of spiders who like to catch and eat fish. The one in the photograph above is about 70 mm long and lives in a garden pond near Brisbane.
Sometimes the fish are more than twice as long and four times as heavy as the spiders.
And it can take a spider many hours to digest its catch.
The spider will typically anchor its hind legs to a stone or a plant, with its front legs resting on the surface of the water, ready to ambush.
The fish will then be dragged to a dry place before the feeding, which usually lasts several hours, can begin.
A paper in the prestigious journal PLOS One by Bradley Pusey from the University of Western Australia, and Martin Nyffeler from the University of Basel in Switzerland, shows for the first time the large diversity of spider families engaged in fishing.
The researchers describe almost 90 incidences of fishing by five families of semi-aquatic spiders, observed at the fringes of shallow freshwater streams, rivers, lakes, ponds, swamps and fens and mostly in warmer places.
They show that fishing is geographically widespread, occurring on all continents except Antarctica. In most cases, the spiders eat fish in combination with other prey, mostly insects.
Associate Professor Pusey says 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.
While spiders usually feed on prey which 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.
Fishing spiders possess large strong mouthparts capable of piercing their preys’ skin and are equipped with powerful venoms containing 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. In some, death is sudden while in others it can take almost an hour.
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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