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Meet the six-spotted fishing spider

Updated on January 7, 2015

Most people, when they think of spiders, think of webs, Halloween, and catching flies. But there are a lot of different types of spiders with different habitats than trees and different habits than wrapping flies in silk.

One such unique genus is the genus Dolomedes – fishing spiders. These interesting arachnids are actually known for catching and dragging fish, aquatic insects and amphibians from the edge of the water for their meals. They do not build webs. Fishing spiders “walk” on water and under its surface; they walk, run, row, glide and dive. These spiders can jump straight up from the water or dive below it when being attacked by a predator. But they are not bound to water; they can walk rapidly on land as well. They can attack larger prey such as small fish, frogs, tadpoles or newts. Predators of fishing spiders include large frogs, fish and birds. Depending on which direction the predator is coming from, the spider will jump or dive. The spiders’ excellent vision allows them to see pray and predators.

Male spiders must beware. If a male approaches a female which has already mated, she will simply eat the male. Once the female has mated, she spins a silk sac to carry the eggs she lays, which she carries in her jaws to a safe place. These sacs are produced between June and September. Once a safe place is found, she makes a shelter out of leaves and stays, guarding her eggs. When the eggs hatch, the mother spider stays around until the babies (spiderlings) are ready to go off on their own after their first molt. The spiderlings will live over two winters before mating themselves.

The six-spotted fishing spider is Dolomedes triton. This species is named after the mythical Greek god Triton, since he is the messenger of the sea and son of Poseidon. They are often called dock spiders because they can be seen scampering through cracks on a boat dock if someone is walking along. Other names are the fishing spider, nursery web spider (its family is nursery web spider, Pisauridae) and raft spider.

The triton is found all across North America, except in the Rockies and Great Plains. It can also be found in southern Canada, Central America and South America. It is more closely associated with water than any of the other fishing spiders, and can be found among aquatic vegetation at the edges of streams and rivers, and floating around in lakes and residential pools. It is a strong hunter.

The mating and egg laying habits are the same as other fishing spiders, but just before the eggs are ready to hatch, the female suspends the sac in a “nursery web” built among foliage. The male does a courtship ritual and may die right after that due to the practice of cannibalism. The young reach their first molt in about a week.

Tritons are fairly large, up to 2-1/2 inches long, including the legs. Females are larger than males. It is relatively easy to identify, with a greenish-brown body with two white stripes on the front section (cephalothorax) of its body and twelve white spots on the rear section (abdomen). Under the abdomen there are six black spots; hence the name. They have eight eyes to achieve their great vision even under water. They like shallow, quiet water such as marshes, ponds and slow-moving streams. They can be found on the shore, on plants, or on the water surface. They like places where there are lots of plants in and around the water, so they can hide from predators and still ambush their prey. They often feed on terrestrial insects which fall into the water and can’t escape. They are diurnal, mostly active during the day, and can wait patiently with their legs spread out until stimulated by prey.

The six-spotted fishing spiders can walk underwater when they climb down a plant leaf or stem below the surface. They can also use their legs as oars to push themselves across the surface. To glide, the triton remains still, getting pushed across the surface by the wind. To dive, the spider traps an air bubble in its legs to allow it to breathe underwater. The triton is known to stay underwater, up to seven inches below the surface, for over half an hour. They will dive underwater and hold onto a plant when frightened, to avoid a predator.

The better known predators of the triton are the bluegill, yellow perch, largemouth bass, channel catfish, creek chub, great blue heron, bullfrog, southern leopard frog, common snapping turtle, black crappie and six-spotted fishing spider.

The most common observed prey of the triton are the crane fly. Common whitetail, eastern dobsonfly, northern caddis fly, field cricket, true katydid, honey bee, wood frog, spring peeper, southern leopard frog, eastern mosquitofish, creek chub, golden shiner, and eastern newt. Note that the bluegill, creek chub and southern leopard frog are both predator and prey – depending on size.

As with all spiders, the six-spotted fishing spiders are very helpful for people, controlling the insect population, and they will only bite in self-defense; they are not considered dangerous. We can leave them alone and let them balance out the ecosystem.

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      Idalee 2 years ago

      I feel so much happier now I unnadsterd all this. Thanks!