Spiders that catch and eat fish exist on every continent of Earth, except for Antarctica, making them more common than was previously thought. Though spiders have traditionally been thought of as eating primarily insects, there are many spiders who regularly dine on fish, as well. A review study that gathered together evidence for the predation of fish by many species of spiders, conducted by Martin Nyffeler, who is a zoologist and spider authority from the University of Basel, Switzerland, and researcher Bradley Pusey of the University of Western Australia, was published on June 18 in the academic journal, PLOS ONE.
Though spiders that eat fish can be found in a variety of habitats, there are perhaps most often found in or near warmer bodies of water that are depleted of oxygen. The Florida wetlands are one good example of where these types of spiders seem to prefer to live. Fish are more likely to come to the surface of the water, which is often richer in oxygen, in such areas.
According to the zoologists who published the study, eight families of spiders (if not even more) are known to prey on and eat fish, and 18 species within those families make fish a regular part of their diets. Five of the eight families have been seen catching and eating fish in nature, and the other three have been shown to prey on fish under laboratory conditions.
The spiders that prey on fish are often smaller than the fish they catch and eat. Some of the spiders seem to prefer eating fish to any other prey, and some spiders are more opportunistic, and will snatch up and eat other prey that is nearby, such as insects, shrimp, or small lizards.
They catch and dispatch the fish by using powerful neurotoxins that also contain enzymes that help break the fish down so that the spiders can more easily consume them. According to spider expert and study co-author, Martin Nyffeler, the fish that the spiders consume could have “substantial nutritional importance” to their life cycles, and might provide crucial nutrition in aiding their ability to produce eggs and reproduce.
Some spiders, such as ones in the genus Trechaleidae or the six-spotted fishing spiders (Dolomedes triton) which live in the United State, anchor their hind legs to a plant of small rock, and have their front legs resting upon the surface of the water, ready to grab any unwitting fish that swims close by. After the spider catches the fish, it drags its prey to a more secluded, dryer place, where it then devours the fish over a period of a few hours.
Over 80 percent of the incidents where spiders have been observed catching and eating fish involve spiders from the Pisauridae family. These spiders have no use for webs, at all. Spiders that prey on and eat fish in this family sometimes dive and swim after their prey, or walk on the surface of the water, searching for insects or their next aquatic meal.
Fishing spiders from the genus Dolomedes, sometimes called raft spiders, are known for their behavior of preying on fish, and they will occasionally kill fish even when they are not particularly hungry, like they did at a fish-rearing pond in Oklahoma. They have been spotted near fish tanks like one at the Steinhart Aquarium in San Francisco, where one such spider dispatched and ate several fish over the course of only a few days.
Other spiders that prey on and eat fish include two species in the Ctenidae family, both belonging to the genus Ancylometes, that use air bubbles to get oxygen while the dive after fish. They can stay underwater for up to an hour.
One of the smallest spiders that has been known to prey on and eat fish is from the Lycosidae family. It is the pond wolf spider, and is only one centimeter long, but it is a skilled killer of fish. With the pond wolf spider and the others, the fish can be up to five times as heavy as they are. For instance, a spider from the Liocranidae family that was less than a centimeter in length was seen by researchers in France catching and eating a small trout that was approximately 2.8 times larger in size.
The diving bell spider is the only spider that is known which lives its entire life under water. They build webs that are shaped like domes between underwater plants. When they catch a fish, their venom is potent enough that it kills the fish within a matter of a few seconds.
The two researchers who published the review study, Bradley Pusey and Martin Nyffeler, collected together all of the Internet posts and published reports that they found about spiders which had been observed eating fish. They found 89 reports in all, half of which had never been previously written about in scientific literature. The number of the reports they collected made the two researchers realize that spiders which ate fish were more common and widespread than they had thought. Their study, about spiders which eat fish, documented that fish-eating spiders live all around the world, except for Antarctica.
Written by: Douglas Cobb