In the words of Michael Roberts:
When at rest or sensing prey, they often extend the first and second legs and hold them together, straight out at an angle. Pisaura does this on vegetation, sitting quite still with the first pairs of legs held up, and seems almost like a dog sniffing the air.
In the summer, the young spiders mature and males wrap a captured prey into a silk parcel as a nuptial gift for the female, a unique behaviour amongst spiders. Although this might represent some form of paternal care, it is likely that it originated as a way for the male to protect himself from sexual cannibalism, which is very common in spiders, and also occurs in Pisaura, often before mating takes place. The male will carry the gift around until he finds a mature female. He will offer her the gift in a ritualised way and if she accepts it and starts feeding on it, copulation will ensue. Females not being offered a gift will not mate. Occasionally the female will interrupt mating and the males display another unusual reproductive behaviour: if the female behaves aggressively or tries to snatch the gift, the male will feign death, a common antipredator behaviour in spiders called thanatosis. He will remain motionless, with legs stretched while being dragged by the female, but still hanging onto his nuptial gift with his jaws. If the female starts opening the present and feeds, the male "comes alive" again and mates. Feigning death is a behaviour that increases male reproductive success, as was shown in experiments by Line Spinner Hansen and coworkers. They found that males feigning death have more copulatory success than males who don't. They explain these results by the fact that males feigning death achieve longer copulations, and are able to continue in contact with the female and resume mating later, for example when females try and run away with the gift.
(from Spinner Hansen et al 2008)
Females make quite large, pale egg sacs which they hold under their bodies with their jaws and palps (top and above), and walk awkwardly on tiptoes white they do this. When the female senses that eggs are about to hatch she constructs a nursery.
Roberts, M.J. (1995) Spiders of Britain and Northern Europe. Harper Collins, London.
Spinner Hansen, L., Gonzales, S., Toft, S., & Bilde, T. (2008). Thanatosis as an adaptive male mating strategy in the nuptial gift-giving spider Pisaura mirabilis. Behavioral Ecology, 19 (3), 546-551 DOI: 10.1093/beheco/arm165
Bilde T, Tuni C, Elsayed R, Pekár S, & Toft S (2006). Death feigning in the face of sexual cannibalism. Biology letters, 2 (1), 23-5 PMID: 17148316