Steatoda nobilis
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| Steatoda nobilis | ||||||||||||||
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| Steatoda nobilis (Thorell, 1875) |
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Steatoda nobilis, commonly known in England as the biting spider or the false black widow (though several other species are known by the latter name), is a common species of spider in the genus Steatoda. As one of this spider's common name indicates, the spider superficially resembles, and is frequently confused for, the black widow and other venomous spiders in the genus Latrodectus. The spider is native to the Canary Islands but arrived in England in around 1870 through bananas sent to Torquay.[1] In England it has a reputation as one of the few local spider species which is capable of inflicting a painful bite to humans - although this is a comparatively rare occurrence.
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[edit] Description
Like true widow spiders, S. nobilis has a round, bulbous, over-sized abdomen, which is darkly colored. Females typically have pale marble like markings on the dorsal side of the abdomen, with a cream-coloured band and range in size from 7mm to 14mm. Males tend to have smaller more elongated abdomens, with pale brown legs and dark brown, less patterned markings. When a mature male is ready to mate you can see his pedipalps (the mouth feelers) expand into carrot shaped balloons to accommodate a sperm covered silk sheet, ready for mating.Males of this genus are able to produce sounds during courtship by scraping teeth on the abdomen against a file on the rear of the carapace.
[edit] Habitat and range
In common with other members of the Theridiidae family, S. nobilis constructs a cobweb, i.e., an irregular tangle of sticky silken fibers. As with other web-weavers, these spiders have very poor eyesight and depend mostly on vibrations reaching them through their webs to orient themselves to prey or warn them of larger animals that could injure or kill them.
[edit] Distribution
The spider is found in the Canary Islands, in England around Hampshire, Isle of Wight and Cornwall, Dorset and Essex [2], and in Madeira; it has also been observed in parts of continental Europe and Africa. [3].
[edit] Population Growth in UK
The False Widow population is expected to grow dramatically in the UK due to global warming. Experts predict that in a few years they will be in every garden in the south of England and more will be spotted higher up the country. The False Widow spider first arrived in banana shipments from the Canary Islands in around 1870. [4]
This prediction was made by Stuart Hine of the Natural History Museum and spun into a set of alarmist tabloid articles. Stuart responded on the naturenet blog, stating, "Of course I also explain the great value of spiders and how rare the event of spider bite in the UK actually is. I also always explain that up to 12 people die from wasp/bee stings in the UK each year and we do not panic so much about wasps and bees – but this never makes it past editing." [5]
[edit] Medical significance
They are not aggressive, and most injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched somehow. It is possible that some bites may result when a spider mistakes a finger thrust into its web for its normal prey, but ordinarily intrusion by any large creature will cause these spiders to flee.
The bite of S. nobilis is known to be medically significant in humans, however without any long-lasting effects. The bite of this spider, along with others in the genus Steatoda, can produce a set of symptoms known as steatodism. Symptoms of bites include intense pain radiating from the bite site, along with feverishness or general malaise. [6] In 2006 a Dorchester man spent three days in Dorchester County Hospital with symptoms of heart seizure, after suffering a spider bite believed to be caused by S. nobilis. (A spider was observed in the act of biting the man; however it was not captured and positively identified by an expert).[1]
The bite of S. nobilis, like other Steatoda spiders is far less dangerous to humans than that of true black widows.
[edit] References
- ^ a b David Sapsted. "Watch out, the black widow's sister is ready to bite you"", Daily Telegraph, 2006-11-17.
- ^ Biting spider widens its web. BBC News (2001-09-21).
- ^ http://www.britishspiders.org.uk/html/bas.php?page=world&taxon_key=NBNSYS0000039460 British Agricultural Society: World Distribution Map of S. Nobilis
- ^ Source: ITN News 05th May 2007
- ^ The Ranger's Blog: The truth about Steatoda nobilis - is it the UK's most dangerous spider?
- ^ D. A. Warrell, J. Shaheen, P. D. Hillyard & D. Jones (1991). Neurotoxic envenoming by an immigrant spider (Steatoda nobilis) in southern England. Toxicon 29 (10): 1263–1265. doi:.
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