Wednesday, 22 June 2011

Nursery web spiders

ResearchBlogging.orgThe nursery web spider, Pisaura mirabilis, is a striking, handsome spider with a surprising range of behaviours. A large spider, with long, but solid, legs and a long, tapering abdomen, it is quite variable in colour, but it always has a pale band in the middle of the carapace, flanked by darker bands. It is found in a range of habitats including grassland, meadows, woodland rides and gardens. Pisaura does not build a web, rather it is an active, highly visual hunter on low vegetation or the ground.
  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. 
She opens the egg sac and folds some blades of grass and builds a loose tent of silk strands around them. The she mounts guard just underneath her nursery. When the spiderlings hatch around midsummer, they form a cluster in a similar way to the Garden Spider, in the safety of their tent, where remain until after their second moult they disperse. I found the one above this afternoon in my local wildlife garden. The spiderlings are visible at the edge of the tent. I am so pleased to have a thriving population of this amazing spider living at my doorstep.

References
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

15 comments:

lotusleaf said...

Interesting information. Thanks.

Lucy Corrander Now in Halifax! said...

I've been puzzling about web-tents in the grass where I live (coast of Dorset). The little spiders are hatched and dispersed about the tent unless disturbed - when they gather into a pillar shape. There's a structure in there reminiscent of the papery nature of a wasp's nest - though once the tent is opened it may look different. The little spiders are dark in colour. The thing is, I haven't seen any mother spiders standing guard.

Wondering if these might be the spiders you mention here.

I'll be including them in a post in the next few days and will put a picture - but I'm trying to find out at least a guess in advance.

Africa Gomez said...

Thank you for your comment Lucy, I think it is very likely your tents belong to this species as I am unaware of any other species which does this. The papery structure inside is the egg sac. I am not sure when the mother leaves, but often she is somewhere on the side or underneath the tent. Look forward to your post.

Lucy Corrander Now in Halifax! said...

Thanks Africa. I'll let you know when I post. The nests I am seeing round here are much bigger than the one you have in your picture - I should go and measure but by memory they are something like three inches high by four wide. They are bit sprawly so vary in dimensions. They also seem to be suspended from a thick grass/chopped stalk tent pole rather than within a curved grass leaf.

I'm looking forward to seeing them when they leave their nests. They are very small at present so I imagine they have quite a bit of growing left to do. I also guess I'll go along one day and find they've dispersed before I've had the chance to see them grown!

MR SPIKE said...

My House is filled with them. beginning of spring you start seeing them and then in summer time I see at least 2 or 3 of them in a day some are large, they love my house for some reason although they are cool I don't really like them so much I am scared of them especially because there are so many and I also find them in my cloths or shoes, could someone perhaps tell me why I have so many of them breeding in my house ? I don't want to kill them but I have a son and don't want them to bite my him, he is also fearless and want to play with them so please give me suggestions on what I can do or should do.. Thanks :)

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