Monday, 4 April 2011

Ground Crab Spider

ResearchBlogging.orgUntil a couple of weeks ago, I was under the mistaken impression that there were no crab spiders in the north of the U.K. Although this is true for flower crab spider, Misumena vatia, a chamaleon-like hunter that changes colour to match the flower is sitting on, there are many other species that are widely distributed, in the U.K. as I found out through a thread in Wild About Britain. All crab spiders have some ability to change colour to match their surroundings and become invisible to their unsuspecting prey. They do not build a web to hunt, instead, they rely on their superb camouflage and their front two pairs of legs, larger than the rest and furnished with forward facing spines, which they keep open when hunting, forming like a living trap. Their's is a stalking strategy, sitting with its outstretched legs waiting for invertebrates to turn up. The name crab spiders suits them well, as their oversized front legs, divergent lateral eyes and sideway walking makes them look like miniature crabs. One of the most widespread crab spider is Xysticus cristatus. This crab spider is found on the ground or on low vegetation, although it can also hunt in flowers. The female above was sunbathing on my conservatory frame on an awkward corner for photos. I captured it and took a few shots in the while bowl. I released it on a dandelion (above) - before I found out about its preferred hunting grounds - but she didn't like it and scuttled away relatively quickly.
Xysticus cristatus female on her crab-like stance
Unlike flower crab spiders, which feed mainly on pollinators - bees, hoverflies and butterflies - ground crab spiders feed on a wide range of prey, from small prey such as ants aphids and springtails to the larger bees and butterflies, and other spider species, even earthworms! (see Figure below from Nyffeler & Breene). Birkhoffer and coleagues found that Xysticus cristatus - together with wolf spiders - eat larger proportions of aphids when compared to web building spiders. Their common aphid prey might make them a suitable biological control, retarding the population growth of aphids during spring so the authors suggested to encourage habitats favourable to these spiders near crops.
References
Nyffeler, M., & Breene, R. (1990). Spiders associated with selected European hay meadows, and the effects of habitat disturbance, with the predation ecology of the crab spiders, Xysticus spp. (Araneae, Thomisidae) Journal of Applied Entomology, 110 (1-5), 149-159 DOI: 10.1111/j.1439-0418.1990.tb00108.x
Birkhofer K, Gavish-Regev E, Endlweber K, Lubin YD, von Berg K, Wise DH, & Scheu S (2008). Cursorial spiders retard initial aphid population growth at low densities in winter wheat. Bulletin of entomological research, 98 (3), 249-55 PMID: 18439342

4 comments:

Phil said...

Fascinating - you've put a name to a spider that I've see in my garden on a few occasions. Thanks.

Blackbird said...

Great to be of help Phil! I just updated the post with some more info on these fascinating spiders.

animaloftheday said...

I've found an all-white species of crab spider in hull before. Sadly i didn't think to take a picture or fully ID it at the time.

Blackbird said...

HI animaloftheday, wow, that is very interesting, thank you for letting me know. I know of no other white spider but Misumena vatia. I was checking the distribution yesterday and the northernmost location is Lincoln, although there are older sightings around Lincolnshire. You can check its distribution in the NBN gateway or in the British Arachnological Association website (links on the right of the blog).