A study conducted on spider predation around the world shows that a number of spiders prey on fish to supplement their diet of insects. They sometimes consume even those fish that are 4.5 times their body weight.

Researchers documented the wide-ranging palate of spiders in a study which gave detailed information as to how almost two dozen species of spiders, which thrive on every continent except Antarctica, eat small freshwater fish that is bigger than them in size.

The researchers estimated 90 incidents of fish predation by five families of semi-aquatic spiders, which have been observed at the fringes of shallow freshwater streams, rivers, lakes, ponds and swamps, mostly in warmer places. They show that fish predation is widespread geographically. In most cases, the spiders eat fish in combination with mostly insects or other prey.

Vision plays a very less role in detection of prey. Some spiders rely on feeling ripples in the water, which are made by their prey, still some other rely on the dorsal fin of a fish touching their outstretched legs. Some spiders also anchor their hind legs to a stone or plant and their front legs rest on the surface of the water with them being ready to sense and ambush their dinner.

Fishing spiders have large strong mouthparts which are capable of piercing the skin of their prey and have powerful venoms that contain hundreds of neurotoxins. Fish are bitten by the spiders at the base of their head and in some cases, death is sudden while in others it takes almost an hour.

Once a spider catches the fish, it drags it to a dry place before it eats it. This is because of the fact that the spider has to pump enzymes into the fish before it can be digested and also since there is less chance of the fish to get away. It takes a spider many hours to consume a fish and the extra nutrients as well as calories in a fish as compared to an insect may give the spider an added advantage during the mating period.