Steatoda nobilis

Steatoda nobilis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Arachnida
Order:	Araneae
Family:	Theridiidae
Genus:	Steatoda
Species:	S. nobilis
Binomial name
Steatoda nobilis (Thorell, 1875)

Steatoda nobilis is a spider in the genus Steatoda, known in the United Kingdom as the noble false widow^[1][2] and often referred to as the false widow.^[a] As the common name indicates, the spider superficially resembles and is frequently confused for the black widow and other spiders in the genus Latrodectus, which can have medically significant venom. Steatoda nobilis is native to Madeira and the Canary Islands from where it allegedly spread to Europe,^[3] and arrived in England before 1879, perhaps through cargo sent to Torquay.^[4] In England it has a reputation as one of the few local spider species which is capable of inflicting a painful bite to humans,^[5] with most bites resulting in symptoms similar to a bee or wasp sting.^[6]

Description

Steatoda nobilis has a brown bulbous abdomen with cream coloured markings that are often likened to the shape of a skull.^[7] The legs are reddish-orange.^[8] Females range in size from about 9.5 to 14 mm in size, while males are 7 to 11 mm.^[1] Males are able to produce stridulation sounds during courtship, by scraping 10-12 teeth on the abdomen against a file on the rear of the carapace.

Male with swollen pedipalps

Distribution, habitat and ecology

The spider is an introduced species across Europe, plus parts of North Africa, and likely spreading. It was found for the first time in 2011 in Cologne, Germany.^[9] It is originally from the Canary Islands and Madeira.^[10] In England it has been reported mostly in southern counties,^[11][12] but its range appears to be expanding northwards.^[13][14] In 2011, the spider was reported as an established invasive species in the USA, in Ventura County, California.^[15]

As with other members of the family Theridiidae, Steatoda nobilis constructs a cobweb which is an irregular tangle of sticky silken fibres. Its 'scaffold web' differs from others of the genus in the exceptional strength of the silk, and in the tubular retreat that is at least partly concealed in a deep crack or hole.^[12] They have 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.

Population expansion in UK and Ireland

Steatoda nobilis, Hampshire, England

The distribution of Steatoda nobilis is expected to increase northwards in the UK, due to, at least partly, mild winters in recent years. This prediction was reported by Stuart Hine of the Natural History Museum,^[16] and is substantiated by the National Recording Scheme.^[12]

The spider is reported to be an established species in Ireland.^[17]

Medical significance

Female of Steatoda nobilis in Hampshire

Like almost all spiders, Steatoda nobilis is venomous, but its bite is almost exclusively of mild effect on humans, without the severe consequences that can occur with black widow spiders. Its bite is often alleged to be one of the medically significant for humans, even though the few recorded bites do not typically present long-lasting effects. The symptoms of a bite are typically similar to a bee or wasp sting.^[8] 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.^[18]

Media reaction

Sensationalised stories about the bite of Steatoda nobilis have featured in UK newspaper articles.^[19][20] Stuart Hine from the Natural History Museum, London 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." ^[16] Steven Falk, an entomologist, cautioned that without "hard evidence", it is difficult to know how many of the bites reported in the media have been caused by false widow spiders.^[21]

Alleged incidents

• In 2006 a Dorchester man spent three days in Dorset County Hospital with symptoms of heart seizure, after suffering a spider bite believed to be caused by Steatoda nobilis.^[5]
• In 2012 a man collapsed in Southampton after apparently being bitten on his neck. He had complained of feeling hot, queasy and light headed. He required treatment in hospital, where it was discovered that he had been bitten 10 times on the neck, allegedly by the same large spider. The spider (which had been trapped in the victim's hooded jacket) was caught and tentatively identified by health workers as Steatoda nobilis.^[22]
• In 2012 a woman in Dorset suffered serious effects after her hand was supposedly bitten by a false widow spider.^[23]
• In 2013 a man in Sidcup of London was allegedly bitten in his sleep, reporting that his hand had turned black and yellow. His hand remained swollen for five weeks until doctors gave him a course of antibiotics.^[24]
• In October 2013, it was reported that a man from Romford in Essex had been allegedly bitten by a false widow. He was treated for bacterial infection with antibiotics and needed to have his leg drained of pus.^[25]
• In October 2013, a British school in the Forest of Dean was closed for a day for fumigation as a result of a dense population Steatoda nobilis on the site.^[26]
• In 2014, a woman from County Durham had her left index finger amputated after contracting the flesh-eating bug necrotising fasciitis following a claimed bite from a false widow spider.^[27][28]
• In October 2014, an Irish man went into cardiac arrest and spent a day in intensive care after being bitten three times by what was claimed as a false widow, on the hip, side and shoulder.^[29]

Notes

a. ^{^} The correct and full English name for Steatoda nobilis is "Noble false widow". Media coverage usually abbreviates this to "false widow", although Steatoda nobilis is strictly speaking one of the false widows. Steatoda grossa^[30] and Steatoda paykulliana^[31] are other examples of false widow spiders.

References

External links

Wikimedia Commons has media related to Steatoda nobilis.

• World Spider Catalog: Family Theridiidae
• UKSafari.com: False widow spiders
• Steatoda nobilis images
• PatientPlus: Spider bites
• BBC video of Steatoda nobilis