What’s Eating You? Noble False Widow Spider (Steatoda nobilis)

Incidence and Characteristics

The noble false widow spider (Steatoda nobilis) is one of the world’s most invasive spider species, having spread across the globe from Madeira and the Canary Islands into the North Atlantic.^1,2 Steatoda comprise multiple species of false widow spiders, named for their resemblance to black widow spiders (Latrodectus). The noble false widow spider is the dominant species in buildings in southern Ireland and Great Britain, with a population surge in 2018 that caused multiple temporary school closures in London, England, for fumigation.³ The noble false widow spider was first documented in the United States in Ventura County, California, in 2011, with numerous specimens found in urban areas (eg, in parks, underneath garbage cans) closer to the coastline as well as farther inland. The species may have been introduced to this area by way of Port Hueneme, a city in California with a US naval base with routes to various other military bases in Western Europe.⁴ Given its already rapid expansion outside of the United States with a concurrent rise in bite reports, dermatologists should be familiar with these invasive and potentially dangerous arachnids.

The spread of noble false widow spiders is assisted by their wide range of temperature tolerance and ability to survive for months with little food and no water. They can live for several years, with one report of a noble false widow spider living up to 7 years.⁵ These spiders are found inside homes and buildings year-round, and they prefer to build their webs in an elevated position such as the top corner of a room. Steatoda weave tangle webs with crisscrossing threads that often have a denser middle section.⁵

Noble false widow spiders are sexually dimorphic, with males typically no larger than 1-cm long and females up to 1.4-cm long. They have a dark brown to black thorax and brown abdomen with red-brown legs. Males have brighter cream-colored abdominal markings than females, who lack markings altogether on their distinctive globular abdomen (Figure). The abdominal markings are known to resemble a skull or house.

^{©ePhotocorp / iStock / Getty Images Plus.}

Noble false widow spider (Steatoda nobilis).

Although noble false widow spiders are not exclusively synanthropic, they can be found in any crevice in homes or other structures where there are humans such as office buildings.^5-7 Up until the last 20 years, reports of bites from noble false widow spiders worldwide were few and far between. In Great Britain, the spiders were first considered to be common in the 1980s, with recent evidence of an urban population boom in the last 5 to 10 years that has coincided with an increase in bite reports.^5,8,9

Clinical Significance

Most bites occur in a defensive manner, such as when humans perform activities that disturb the hiding space, cause vibrations in the web, or compress the body of the arachnid. Most envenomations in Great Britain occur while the individual is in bed, though they also may occur during other activities that disturb the spider, such as moving boxes or putting on a pair of pants.⁵ Occupational exposure to noble false widow spiders may soon be a concern for those involved in construction, carpentry, cleaning, and decorating given their recent invasive spread into the United States.

The venom from these spiders is neurotoxic and cytotoxic, causing moderate to intense pain that may resemble a wasp sting. The incidence of steatodism—which can include symptoms of pain in addition to fever, hypotension, headache, lethargy, nausea, localized diaphoresis, abdominal pain, paresthesias, and malaise—is unknown but reportedly rare.^5,10 There are considerable similarities between Steatoda and true black widow spider venom, which explains the symptom overlap with latrodectism. There are reports of severe debilitation lasting weeks due to pain and decreased affected limb movement after bites from noble false widow spiders.^10-12

Nearly all noble false widow spider bite reports describe immediate pain upon bite/envenomation, which is unlike the delayed pain from a black widow spider bite (after 10 minutes or more).^6,13,14 Erythema and swelling occur around a pale raised site of envenomation lasting up to 72 hours. The bite site may be highly tender and blister or ulcerate, with reports of cellulitis and local skin necrosis.^7,15 Pruritus during this period can be intense, and excoriation increases the risk for complications such as infection. Reports of anaphylaxis following a noble false widow spider bite are rare.^5,16 The incidence of bites may be underreported due to the lack of proper identification of the responsible arachnid for those who do not seek care or require hospitalization, though this is not unique to Steatoda.