The Woodlouse Spider: Dysdera crocata
Woodlouse Spider Dysdera crocata. 
By Mgeorge733
With a carapace of lustrous crimson and an abdomen of subtle cream I think this is one of the most striking spiders in the UK.
Although superficially resembling D. erythrina, D. crocata is a slightly larger spider with adult females reaching 11-15mm, the male slightly smaller at 9-10mm (Roberts, 1995). The fangs look like they could deal some damage and so they should as the main prey of this species is the hard bodied woodlouse.
Of all the spiders in the world only around 500 species can be of any harm to people or even have jaws strong enough to penetrate human skin (Roberts, 1995). In the UK we have around a dozen that can cause an unpleasant bite, usually a last resort for the spider if it feels threatened. The pain has been likened to a nettle or bee sting, disappearing after an hour (Natural History Museum, 2013). You can follow the link here to a section of the Natural History Museum site where they outline bite cases in the UK.
So where would you find this species? It can be found all over southern England and is widespread in Europe though it has never been located further north than Denmark in Scandinavia. Log piles, stones and debris are common residence for this species and they will be found in gardens if it is wet enough (their woodlice prey require damp conditions to breathe properly). The woodlouse spider is nocturnal and appears active all year round but populations peak around mid summer and autumn (Smithers, 2013). Prey is pursued on foot as the spider does not build a web. It does, however, build a silken cell where it hides out during the day.
Since 1820 when it was first recorded around 2260 records have been made in the British Isles (Smithers, 2013). The species has now been introduced into Japan, North and South America, Australia, New Zealand and South Africa (Natural History Museum, 2013).
References
- Anon. (2013) NaturalHistoryMuseum. Woodlouse spider, Dysdera crocata. Available at: http://www.nhm.ac.uk/nature-online/life/insects-spiders/identification-guides-and-keys/spider-bites/woodlouse-spider.html
- Roberts, M.J. (1995) Colins Field Guide: Spiders of Britain & Northern Europe. HarperCollinsPublishers.
- Smithers, P. (2013) Spider and Harvestman Recording Scheme Website: the national recording scheme for spiders and harvestman in Britain. Summary for Dysdera crocata (Araneae). Available at: http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Dysdera+crocata
