The nursery web spider Pisaura mirabilis is a spider species of the family Pisauridae.
Striking characteristics of Pisaura mirabilis are its long legs (the fourth pair being the longest) and its slender abdomen (opisthosoma). The male is between 10 and 13 mm, while the female is 12 to 15 mm. After final ecdysis, the male spiders weigh on average 54 mg and females 68 mg.
The prosoma (cephalothorax) is variable in color, ranging from light to reddish brown and from gray to black. A lighter stripe is visible down the middle of the prosoma. The opisthosoma (abdomen) is long and narrow and tapered towards the rear end.
The female spiders has a dark patch (epigyne) on the underside of her abdomen that includes the copulatory organs. Male genital openings can be found at the same location, but remain inconspicuous.
Patterning and coloration varies due to polymorphism. These patterns, which can be caused by hair and pigments, change with the growth of the spider (ontogenesis).
Male spiders are stronger in contrast than females and look black, especially in comparison to the white nuptial gifts. Females tend to get paler towards the end of summer. The stripe along the back of the body can be found in all spiders and can be seen as crypsis, a protective measure against predators.
