six-spotted fishing spider

Six-spotted fishing spider is a large, robust, nursery web spider. It is one of the largest spiders encountered in Minnesota. The adult female body is dark brown with light markings and ⅝″ to ¾″ long with a legspan of 2″ to 3″.

The front part of the body (cephalothorax) is about the same size as the rear part (abdomen). The covering (carapace) of the cephalothorax is dark gray to brown or greenish-brown with a bold, silvery-white to yellow stripe along each side. There is often a narrow pale center (middorsal) line and two shorter lateral lines that form a poorly developed trident shape.

The abdomen is dark gray to brown, rounded in the front, widest in the middle, and tapers toward the rear. There is a broad white stripe running down each side and two rows of six small white spots on the upper (dorsal) surface. The spots are usually prominent, sometimes barely discernible. The underside (sternum) is paler. There are six large black spots between the leg bases. This is the feature that gives the spider its common name.

The legs are long, thin and dark brown with thin, pale, longitudinal stripes. They are not horizontally banded. They are covered with hairs and have long black spines. The last leg segment (tarsus) has 3 claws, but these are not visible without magnification.

The male is similar to the female but only about half the size.

Female Body Length: ⅝″ to ¾″

Male Body Length: ⅜″ to ½″

Legspan: 2″ to 3″

Dark fishing spider (Dolomedes tenebrosus) is larger. It lacks the bold white stripes on the cephalothorax and abdomen. The legs appear horizontally banded, not longitudinally striped.

Ponds, lakes, swamps, slow-moving streams

Six-spotted fishing spider does not produce a web to catch prey. The female produces a nursery web for its young.

It is active during the day. It floats, and can run across the water surface like a water strider. When hunting, it perches on floating vegetation, detecting ripples and vibrations in the water with three of its front legs. It sometimes dives up to 7″ for prey or to escape a predator. It can create a bubble of air that allows it to stay under water for a half hour or more.

Mating takes place between June and September. It may be the last act of the male, as the female is cannibalistic. After mating, the female produces a large egg sac, 5 ⁄16″ to ⅜″ in diameter, into which she begins laying eggs. She carries the egg sac around with her mouth as she wanders about. While carrying it, she cannot feed. When the eggs are about the hatch she attaches the sac between leaves in a shelter (nursery) which she has created. She then guards the nursery until the hatchlings disperse in about a week.

Immature adults hibernate near water under stones, under loose bark, or other debris. Males mature and mate in the spring of the first year. Females mature in two years.

Aquatic insects, small tadpoles, tiny fish, other insects that fall on the water surface

Sources

24, 27, 29, 30, 82, 83.

Widespread

I found this guy on my Russian sage at noon today.

Lebanon Hills Regional Park. Near the fishing pier on McDonough Lake

Pisauridae (Nursery Web and Fishing Spiders)
Judy Gallagher

Scary Spider Under Water! - Six spotted fishing spider.
Nature Now! - Chris Egnoto

Six-spotted Fishing Spider (Pisauridae: Dolomedes triton) Lateral Close-up
Carl Barrentine

Six-spotted Fishing Spider Male and Female (Dolomedes triton)
Nature in Motion

Six-spotted Fishing Spider striking and diving in slow motion (Dolomedes triton)
Nature in Motion

Location: Houston County, MN

I found this guy on my Russian sage at noon today.

Location: Lebanon Hills Regional Park

Near the fishing pier on McDonough Lake