Research Article |
Corresponding author: Tobias Bauer ( tobias.bauer@smnk.de ) Academic editor: Wolfgang Nentwig
© 2019 Tobias Bauer, Stephan Feldmeier, Henrik Krehenwinkel, Carsten Wieczorrek, Nils Reiser, Rainer Breitling.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Bauer T, Feldmeier S, Krehenwinkel H, Wieczorrek C, Reiser N, Breitling R (2019) Steatoda nobilis, a false widow on the rise: a synthesis of past and current distribution trends. NeoBiota 42: 19-43. https://doi.org/10.3897/neobiota.42.31582
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The Noble False Widow, Steatoda nobilis (Thorell, 1875) (Araneae, Theridiidae), is, due to its relatively large size and potential medical importance, one of the most notable invasive spider species worldwide. Probably originating from the Canary Islands and Madeira, the species is well established in Western Europe and large parts of the Mediterranean area and has spread recently into California and South America, while Central European populations were not known until 2011.
We report on long-time observations that reveal that at least two flourishing populations in Germany (Cologne) have been present for over five years, while in Ecuador one population has been observed between 2014 and 2018 and several other records were made in other parts of the country. Data obtained from the British Spider Recording Scheme demonstrate that the species moved significantly northwards since the report of the first populations in the very South of England, after several decades of relative stasis. The sudden northward expansion highly correlates with a massive rise in press coverage of the species.
In the Americas, S. nobilis is currently known from four countries (USA, Chile, Ecuador, Colombia), and available DNA barcoding data obtained for specimens from this area suggest that multiple introductions occurred within each country. Using ecological niche modeling, we identified suitable climate regions for the species and discuss possible reasons for its current spread. We propose that seaside cities and villages with a temperate oceanic or Mediterranean climate are especially favourable potential habitats for S. nobilis and will face the highest colonization pressure in the future, while tropical upland regions with temperate climates are also vulnerable to invasion by S. nobilis.
alien species, araneism, biological invasion, citizen science, spider, steatodism
With currently over 47 000 described species, spiders (Araneae) represent a hyperdiverse and extraordinarily variable arthropod group inhabiting nearly every terrestrial habitat on the globe (
Members of the spider family Theridiidae, also known as tangle-web or cobweb spiders, are among the most successful alien spider species (
Steatoda nobilis (Thorell, 1875), one of the largest theridiids and sometimes called false widow or noble false widow, is often mistaken for a Latrodectus species. This species is able to inflict a painful bite often accompanied by swelling, erythema, and pruritus, but normally no systemic effects occur after a bite incident (
Probably native to the Canary Islands and Madeira and first described from the latter (
Although alien populations of S. nobilis are known today from England, Ireland, several parts of the Mediterranean area, California, and Chile (
Recently, we became aware of two established populations in Cologne, Germany, and collected S. nobilis in domestic settings in urban areas in the uplands of Ecuador. Both of these records are in accordance with the current spread of S. nobilis into new and sometimes unexpected habitats and areas all around the world. To further explore the distribution of S. nobilis, we collated all known distribution data together with a large citizen science dataset from Great Britain and performed several analyses of the current distribution trends on a global and local scale, including a global species distribution model. The aim of the work is to present a brief review of the invasion history of S. nobilis, describe current and potential future problems with this invasive species, and to identify regions which are suitable for future invasion.
Spiders were observed and collected by CW during several surveys at two localities in Cologne, Germany, in 2011–2017, with at least one survey per year. In Ecuador, several specimens were collected unsystematically by NR during a field trip in 2014. Collected specimens were identified using
Federal state | City | Location | Habitat | First collection | Status | Literature |
---|---|---|---|---|---|---|
BW | Stuttgart | 48.8268N, 9.1677E | Wall of house | 19.X.2018 | ? | Own data |
NRW | Cologne | 50.9657N, 6.8690E | Garden centre | 10.X.2011 | Established | Own data |
NRW | Cologne | 51.0139N, 6.9139E | Garden centre | XI.2011 | Established | Own data |
Berlin | Berlin | Not specified | Flower wholesale trade | 2012–2013 | Single observation |
|
BB | Not specified | Not specified | Garden centre | 2012–2013 | Single observation |
|
BW | Balingen | Not specified | Garden centre | 2012–2013 | Single observation |
|
Hamburg | Hamburg | Harbour area | Harbour buildings | Around 1954 | Imports |
|
To assess the global and local distribution as well as the invasion history of Steatoda nobilis, taxonomic and biogeographic literature was surveyed (Suppl. material
To further explore the global distribution of S. nobilis and its climatic drivers we performed additional analyses. We ran a principal component analysis (PCA) of bioclimatic variables (CHELSA climate data;
DNA barcoding data were obtained from the public section of the Barcode of Life Data System version 4 (BOLD), http://www.boldsystems.org/ (last accessed 1 May 2018). Specimens that were not determined to species in the database were identified on the basis of geographical and genetic proximity to identified specimens, as well as habitat information and habitus photographs available in BOLD.
Steatoda nobilis was first described based on specimens from Madeira by
In Germany, the species was one of the most frequently imported spiders with Canarian fruit arriving in the harbour of Hamburg at some point (
Although native to Madeira and the Canary Islands, S. nobilis was probably introduced on the Azores in the 20th century (
The first record for Ireland was published by
In the Americas, the populations in California have to be established only recently.
Steatoda nobilis has also been reported from Morocco (
Steatoda nobilis was collected and observed from autumn 2011 to October 2017 at two garden centres in Cologne, Germany, which are separated by a distance of about 7 km. The first specimen was sighted indoors on 10 October 2011 at a large garden centre located in the west of Cologne (Table
We found S. nobilis in 2014 at several locations in the uplands of Ecuador (Table
Diversity of habitats of Steatoda nobilis in its invasive range. A In the South of England, the species is not only abundant on stone walls and railings along the sea side, but also on man-made structures further inland, such as this bus stop in the coastal resort of Lyme Regis, Dorset, where its webs (inset) typically occur together with those of Zygiella x-notata (Araneidae) B Vicinity of the localities with records of S. nobilis in Ambato-Montalvo (Ecuador), August 2014.
Province | Location | Coordinates | Habitat | Date | Specimens | Leg. |
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Tungurahua | Ambato-Montalvo | −1.3266S, −78.6257W | Brick wall | 10.X.2014 | 1 ♀ | N. Reiser |
Tungurahua | Ambato-Montalvo | −1.3256S, −78.6270W | Wall | 17.X.2014 | 1 ♀ | N. Reiser |
Pichincha | Quito | −0.1857S, −78.4781W | Wall | 07.XI.2014 | 1 juv. | N. Reiser |
Tungurahua | Ambato-Montalvo | −1.3256S, −78.6269W | Wall | 08.XI.2014 | 5 ♀, 2 ♂, juv. | N. Reiser |
Pichincha | Quito | −0.1860S, −78.4795W | On house wall | 10.XI.2014 | 1 ♀ | N. Reiser |
Pichincha | Quito | −0.2199S, −78.5116W | On house wall | 10.XI.2014 | 1 ♂, 2 juv. | N. Reiser |
Cotopaxi | Salcedo | −1.0446S, −78.5902W | House wall near Panamericana | 14.XI.2014 | 1 ♂ | N. Reiser |
Tungurahua | Baños | −1.3970S, −78.4231W | Between drip rail/house wall | 21.XI.2014 | 1 ♀ | N. Reiser |
Tungurahua | Ambato central | −1.2579S, −78.6388W | House wall | 25.XI.2014 | 1 ♀, 1 juv. | N. Reiser |
Tungurahua | Ambato-Montalvo | −1.3256S, −78.6269W | Wall | 04.II.2018 | 5 ♀ , 1 ♂ | J.F. Altamirano |
Together with these new populations, confirmed alien populations of S. nobilis are currently known from over 10 countries on four continents (Table
In Great Britain and Ireland, S. nobilis is very abundant in and around houses, and can be found on typical urban structures, e.g., in houses and on outside walls, concrete fences or hedges (
In the Mediterranean, many of the S. nobilis observations were made in or around cities and villages (e.g.
Global distribution of Steatoda nobilis. es = established and non-indigenous, ? = unclear status, ?? = unverified mentioning, pn = probably native, sp = single specimen record.
Country | Area | Literature | Status |
---|---|---|---|
Spain | Mainland |
|
es |
Balearic Islands | collection SMF | ? | |
Canary Islands |
|
pn | |
Portugal | Mainland |
|
es |
Azores |
|
es | |
Madeira |
|
pn | |
France | South |
|
es |
Corse |
|
es | |
Atlantic coast | presented data | es | |
Italy | Mainland |
|
es |
Sicily | no published records | ? | |
Sardinia |
|
es | |
Great Britain |
|
es | |
Ireland |
|
es | |
Germany | Table |
es | |
Belgium |
|
? | |
Netherlands |
|
? | |
Turkey |
|
sp | |
Iran |
|
es | |
Morocco |
|
?? | |
United States |
|
es | |
Chile |
|
es | |
Ecuador | Table |
es | |
Colombia |
|
es |
In California (
All records in Chile (
On the Mediterranean mainland and in the Americas, over 50 % of all known localities are located within a distance of < 10 km to the coastline (Suppl. material
All in all, S. nobilis seems to establish first in urban environments and is able to build up large populations in a short time. This generates further colonisation pressure on seminatural habitats in the environment of cities, finally leading to the establishment of populations outside the urban area.
To gain further insights into the most likely introduction routes of S. nobilis, we used publicly available DNA barcode sequences (~ 650 bp of the mitochondrial cytochrome c oxidase subunit I gene). We used barcodes for about 20 S. nobilis specimens from California and three specimens from Chile. The barcoded individuals are not identified to species in the BOLD database, but their distinct habitus, documented by photographs provided for many of the specimens, as well as their obvious abundance in synanthropic habitats in Southern California, nevertheless allow an unambiguous identification of the specimens. They form a single barcode cluster (BIN, BOLD:ABA5272, https://doi.org/10.5883/BOLD:ABA5272), without geographic structure, i.e. Chilean and Californian specimens share barcode haplotypes.
The genetic diversity of the Californian S. nobilis sample is relatively high, with an average pairwise distance of 0.78% and a maximum distance (within the Californian population) of 2.12%, compared to a median pairwise distance of 1.5% within Steatoda species with more than five published barcodes.
Additional insights into the changing invasive potential of S. nobilis can be gained from citizen science data obtained from the British Spider Recording Scheme. These show that S. nobilis is widespread in Great Britain and especially abundant in the southern half of the island, with scattered records along the northern coasts (
Increase in Spider Recording Scheme records for Steatoda nobilis in Britain parallels intensified press coverage in the local newspapers (dark blue bars = spider records, light blue line = number of press articles). The sudden massive increase in records seen in the last decade coincides with the first appearance of the species in various other countries far from the native range in the Macaronesian islands.
A principal component analysis of climate variables at native and invasive localities revealed that the two areas differ mainly in their annual temperature range and seasonality (Suppl. material
Global climatic suitability of Steatoda nobilis. Mean Maxent prediction, black dots in insert depict known invasive populations in Europe (insert is not masking suitable areas).
To test our predictions, we conducted a field trip to Granville, Normandy (France). The coastline of the Normandy is predicted as a highly suitable area for S. nobilis by our model and has an oceanic climate similar to the south coast of England. Contrary to the latter, no populations of S. nobilis are yet known from the northern Atlantic coast of France near to the Channel Islands. Nevertheless, we were able to locate a local S. nobilis population in the city area of Granville and collected a single adult female (Fig.
Northward distance (km) of recent records of Steatoda nobilis in Great Britain. Distances are calculated relative to the first known record in the country in Torquay, based on data in the SRS database and in
Steatoda nobilis seemed unable to establish viable populations in either Great Britain or Germany at the time of copious and untreated banana imports (= highest propagule pressure;
The populations found in Cologne described in this work are most probably descendants of specimens introduced with potted plants. Very large amounts of cacti and other succulents are imported every year from the Canary Islands (e.g., by the grower “Canary Cactus”), but
In the Netherlands, a record from the Maasvlakte (
In South America, it seems possible that S. nobilis has been spread and/or is distributed by human assistance along the Panamericana Highway (the most important inland transportation route in South America), as two of the Ecuadorian locations (Ambato and Salcedo) are crossed by the route, and Temuco in Chile is situated on one of the two main southern branches of the route.
The climate exploration and the ability of the distribution model to explain the current distribution of S. nobilis with climate variables revealed that the general distribution is not decoupled from the regional climate. Even though most alien records of S. nobilis were located in urban environments, there is currently much evidence that the species is not restricted to urban areas and has already or will spread into seminatural or natural habitats in the invaded areas, e.g., in the South of England and France (
The rapid east–west spread of S. nobilis in Britain, followed by a much later substantial northward expansion especially since 2010, indicates that the range of S. nobilis initially was not constrained by limited dispersal ability. Interestingly, between 1984 and 2010 there was a period of well-known range expansions in other species (
Could the observed distribution trends in Great Britain just be the result of greater awareness and thus more intense reporting, rather than of actual population growth and range expansion? Fig.
Another possible reason for the spider’s expansion success is evolutionary adaptation, e.g., an ecological niche expansion (
The obvious prediction resulting from this assessment and our model is that the expansion of S. nobilis is likely to continue rapidly in the coming years. The western Mediterranean islands, parts of South Africa, southern Australia, and New Zealand will face the highest risk of colonisation in the future. It is possible that some of these areas, especially the western Mediterranean islands, are already inhabited by S. nobilis and the species has been overlooked, similar to the newly reported population in the Normandy, France. An intensified monitoring and search for S. nobilis in inhabited areas and regions predicted as suitable could therefore reveal the real distribution of the species.
As the DNA barcoding data indicate that S. nobilis is genetically very distinct from its congeners, it is unlikely that the species will hybridize with native species. This was observed for alien Latrodectus hasselti, which hybridized at least in one population with a native Latrodectus species in New Zealand (
We are very grateful to the British Arachnological Society and Peter Harvey from the British Spider Recording Scheme for providing the numerous record data of Steatoda nobilis in Great Britain. A special thank you goes to the numerous naturalists contributing to the British Spider Recording Scheme. Without their constant efforts, the current study would not have been possible in such detail.
We would also like to thank Frank van de Putte for the permission to mention the record from the Netherlands, Theo Blick and Rick Vetter for help with literature, Hubert Höfer for the permission to deposit material in the collection of the
Dataset compilation, niche exploration, species distribution modelling, and additional analyses
Data type: occurences, analyses, background information