Steatoda nobilis is a spider in the genus Steatoda, known in the United Kingdom as the noble false widow, as it superficially resembles and is frequently mistaken for the black widow and other spiders in the genus Latrodectus. It is often referred to as the false widow, although "false widow" is a more general term applied to a wider group of species with this resemblance. It is a moderately medically significant spider, with most bites resulting in symptoms similar to a bee or wasp sting. Some bites may cause more significant harm, partly due to pathogenic bacteria from the spiders.
S. nobilis is spotted all year round, both indoors and outdoors in a variety of habitats including cacti, roadside cuttings, and demolished buildings. The spiders prey on both invertebrates and small vertebrates using an "attack wrap" strategy where silk is wrapped around the victim.
Steatoda nobilis is native to Madeira and the Canary Islands from where it is thought to have spread to Europe, and continued to spread to other parts of the world including the United States, Chile and Colombia. They are considered to be one of the world's most invasive species of spider.
Description
Steatoda nobilis has a brown bulbous abdomen with cream coloured markings that are often likened to the shape of a skull. Their legs are reddish-orange. Both female and male S. nobilis can be distinguished from other spiders of the same genus by their large size and typical colouration. Females range in size from about 9.5 to 14 mm in size, while males are 7 to 11 mm. The largest females are 13.7 mm in size, while the largest males can be 11.66mm in size. The males can be distinguished by their conformation of the palp and by their ventral abdominal markings. The females can be distinguished by their epigyne. The variation in size, shape and markings that have been observed is not thought to be due to location. Spiders found centimetres apart and siblings born from the same egg sac can look very different.
Male and female juvenile spiders are indistinguishable from each other.
Distribution, habitat and ecology
Distribution
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. It is originally from the Canary Islands and Madeira. In England it has been reported mostly in southern counties, but its range was reported to be expanding northwards in the 21st century. In 2011, the spider was reported as an established invasive species in the USA, in Ventura County, California. In January 2016, it was reported that Steatoda nobilis had been found in Chile, the first time that the species had been recorded in the southern hemisphere. Research published in December 2018 showed that it was also established in Colombia and Ecuador. It is considered to be one of the world's most invasive species of spider. Seaside cities and villages with a temperate climate are especially favourable habitats for S. nobilis.
The first recorded observation of S. nobilis in England dates back to 1879. The first recorded observation of S. nobilis in Ecuador was in 2014 at several locations as high as 2800 meters.
Between 1985 and 2010 there was no reporting of large numbers of S. nobilis anywhere, and scientists consider this to be a typical lag phase that is a phenomenon observed in many invasive species. Afterwards there was a large accelerated spread observed all over the globe.
They are able to establish in urban environments and build large populations in a short time.
Habitat
S. nobilis can be found year round, regardless of the climate, and they can be found both indoors and outdoors. They have been observed in a variety of different places from cacti and agave to roadside cuttings and buildings. They have also been found on telegraph poles, concrete fence posts, and ivy growing on walls. In Ireland they have been observed to be restricted to man-made habitats such as on steel, concrete or timber structures in urbanised area and not commonly found in forests or dunes. In another study conducted in Ireland, the adult spiders were exclusively only found on steel, concrete or timber structures in urban areas. In California they have also been observed in urban habitats but have also been observed to spread into natural habitats.
Juveniles are observed living in small crevices and holes, which can make their eradication difficult. In Dublin, juveniles have been observed on vegetation and leaves.
In Ireland, they were observed to be captured by common suburban spiders like the cellar spider or the lace-webbed spider.