27 June 2023

Spiders in the family Pisauridae are commonly called the fishing spiders or nursery web spiders. Though their name suggests habitat selection near water, that is not always the case. I would classify them as large spiders (for Minneosta) and adult female Dolomedes can rival in size the Tigrosa wolf spiders mentioned in the previous post. In fact, due to their size and habits, they are often mistaken for wolf spiders. All of these species have a pretty widespread distribution in Minnesota and are commonly encountered.

Like wolf spiders, female fishing spiders can sometimes be found carrying a round egg sac with them as they traverse the landscape. Unlike the wolf spiders which attach that egg case to the spinnerets at the rear and always seem to be chased by a little round ball, the fishing spiders carry their egg sac using their chelicerae and therefore the egg sac is carried up front or under the body as they walk on their tiptoes (see https://bugguide.net/node/view/827127). Once the young have developed to a point that they are ready to leave the egg case, she finds a suitable location and creates a "nursery web". She often guards the nursery until the spiderlings have emerged and dispersed. An image of a Dolomedes striatus guarding her nest can be seen here: https://www.inaturalist.org/observations/53694419. An image of a D. tenebrosus can be seen here: https://www.inaturalist.org/observations/166245114.

In Minnesota we have 2 genera and 5 species.

The genus Dolomedes is represented by four species in Minnesota that I would divide into two different identification groups.

GROUP 1: brown-gray species
Dolomedes tenebrosus or Dark Fishing Spider is one of the most common species observers have found for the Spiders of Minnesota Project (>500 observations). This species is the most likely member of the genus to be found away from water where they often occur in wooded habitats. The W-pattern on its abdomen typically has white on the lateral portions of the W only. It also has a dark area below the eyes and a relatively unmarked carapace; the lateral edges can sometimes be white. A typical female: https://www.inaturalist.org/observations/166241082. The skinnier male: https://bugguide.net/node/view/2186027.

Dolomedes scriptus or Striped Fishing Spider is very similar in appearance to D. tenebrosus. It also has a W-pattern on the abdomen but the pattern is more bold and often has white along the entire edge of the W (not always). The carapace often has a pale midline and sometimes a lyre-like pattern as well. Some individuals may have white lateral edges to the carapace as well. In my experience, this species is more closely tied to water and I associate them with rocks and cliffs near water. A boldly marked individual: https://www.inaturalist.org/observations/124645587. A white-edged individual: https://www.inaturalist.org/observations/123923653.

GROUP 2: red-brown species
Dolomedes triton or Six-spotted Fishing Spider is commonly found near vegetated wetlands and sometimes can be found hunting for small fish and other aquatic prey on top of the water. The carapace has white sub-marginal stripes that flow into white longitudinal stripes on the abdomen. In the darker median area of the abdomen there are 6 pairs of distinct white spots (usually). A typical individual: https://www.inaturalist.org/observations/4068649.

Dolomedes striatus or Striped Fishing Spider (this is why we use those Latin names) is often found in wetlands, wet prairies and open bogs. This species is similar to D. triton. The white sub-marginal bands on the carapace are typically bolder and the red-brown median area of the carapace is darker adjacent to those white bands (unlike D. triton in which the median area is uniform in color). They also lack the distinct white spots on the abdomen. A typical female: https://www.inaturalist.org/observations/144795766. The very rare fulviatronotatus morph of this species has been found a couple of times in Minnesota and looks unlike any other member of this genus. See https://www.inaturalist.org/observations/184108563.

The last member of this family that is found in Minnesota is Pisaurina mira or American Nursery Web Spider. It is just as likely to be found in shrubs or the herb layer of a woodland as it is in a prairie and I find them often along woodland edges. This species is highly variable in its appearance and some of the drabbest individuals seem to lack any distinct markings at all. These can still be identified by this species' tendency to hold its two pairs of front legs forward and together (sometimes the rear pairs of legs are held together as well). An example of this posture can be seen here: https://www.inaturalist.org/observations/119772945

Examples of P. mira morphs:
"Red Morph": https://www.inaturalist.org/observations/54100189
"Stripe Morph": https://www.inaturalist.org/observations/91207051
"Drab Morph": https://www.inaturalist.org/observations/81516030

Happy spidering!