Animal: Latrodectus spp., Widow spiders
Species
- Latrodectus antheratus
- Latrodectus apicalis
- Latrodectus bishopi
- Latrodectus cinctus
- Latrodectus corallinus
- Latrodectus curacaviensis
- Latrodectus dahli
- Latrodectus diaguita
- Latrodectus elegans
- Latrodectus erythromelas
- Latrodectus garbae
- Latrodectus geometricus
- Latrodectus hasselti
- Latrodectus hesperus
- Latrodectus hurtadoi
- Latrodectus hystrix
- Latrodectus indistinctus
- Latrodectus karrooensis
- Latrodectus katipo
- Latrodectus lilianae
- Latrodectus mactans
- Latrodectus menavodi
- Latrodectus mirabilis
- Latrodectus obscurior
- Latrodectus occidentalis
- Latrodectus pallidus
- Latrodectus quartus
- Latrodectus renivulvatus
- Latrodectus revivensis
- Latrodectus rhodesiensis
- Latrodectus thoracicus
- Latrodectus tredecimguttatus
- Latrodectus umbukwane
- Latrodectus variegatus
- Latrodectus variolus
Taxonomy
Common names
- Red widow, Red-legged widow spider
- Knoppie, Button spider
- Brown widow spider
- Red-back spider
- Knoppie, Button spider, Black widow spider
- Black widow spider, eigentliche schwarze Witwe
- Malmignatte, Karakurt
Distribution
Latrodectus spp.: throughout the world between the latitudes 50° north and 45° south.
- L. antheratus: Paraguay, Argentina
- L. apicalis: Galapagos Islands
- L. bishopi: Central and Southern Florida
- L. cinctus: Africa, Cape Verde Islands, Kuwait
- L. corallinus: Argentina
- L. curacaviensis: Temperate zones of North and South America, Lesser Antilles
- L. dahli: Middle East to Central Asia
- L. diaguita: Argentina
- L. elegans: China, Myanmar, Japan
- L. erythromelas: Sri Lanka
- L. garbae: Colombia (Magdalena Valley)
- L. geometricus: Throughout the world in tropical and warm regions
- L. hasselti: From India and Southeast Asia to Australia and New Zealand
- L. hesperus: Western North America, Israel
- L. hurtadoi: Columbia (Magdalena Valley)
- L. hystrix: Yemen (Socotra)
- L. indistinctus: Namibia, South Africa
- L. karrooensis: South Africa
- L. katipo: New Zealand
- L. lilianae: Spain
- L. mactans: Probably North America only
- L. menavodi: Madagascar, Seychelles, Comoro Islands
- L. mirabilis: Argentina
- L. obscurior: Cape Verde Islands, Madagascar
- L. occidentalis: Mexico
- L. pallidus: Southern Russia, Iran, Syria, Israel, Egypt, Libya, Cape Verde Islands
- L. quartus: Argentina
- L. renivulvatus: Africa, Saudi Arabia, Yemen
- L. revivensis: Israel (Neghev)
- L. rhodesiensis: Southern Africa
- L. thoracicus: Chile
- L. tredecimguttatus: The Mediterranean to China
- L. umbukwane: South Africa
- L. variegatus: Chile, Argentina
- L. variolus: Eastern North America
Biology
Latrodectus species possess a typically round abdomen. The cephalothorax (head and anterior part of the body) appears small in comparison. Eyes arranged in 2 rows (Fig. 4.40b). Body length in females 1–1.8 cm, in males barely more than 0.5 cm. Only female animals cause envenoming in humans.
a
b
Latrodectus mactans
a Appearance. Note the (truncated) hourglass-shaped marking on the ventral surface of the abdomen.
b Carapace with the arrangement of the 8 eyes.
Colouring from shiny black to brownish. L. mactans and L. geometricus possess a red marking in the form of an hourglass or two triangles on the ventral surface of their abdomen, although the shape of this marking may show considerable differences between individuals.
L. geometricus also has markings in the form of geometrical patterns on the dorsal surface of the abdomen. In L. hasselti and L. indistinctus there is usually a red or orange longitudinal stripe along the dorsal surface of the abdomen. In L. tredecimguttatus there may be several red spots distributed over the dorsal surface of its abdomen or there may be none at all. Juvenile animals often have markings that differ from those in adults.
"Black widows" are found in the most varying habitats but usually avoid forested areas. They live in both farmed and unfarmed regions and in some regions are even found in cities. L. tredecimguttatus appears to prefer grain fields in southern Europe. L. mactans, L. hesperus and L. hasselti are frequently found in and around human habitations, e.g. in tool sheds, garages, cellars or outdoor toilets, but also in wood or junk left lying around. Several species at least are typicalsynanthropes and their wide distribution was thus greatly facilitated by humans.
They often construct their webs close to the ground. The webs are very irregular in construction. New threads are constantly added to the old web, which makes the webs very stable. The centre of the web is usually located under a stone or branch or in a crack in a wall and forms a basket-like recess which the spider retreats into.
Widow spiders are not at all aggressive and practically only ever bite when squashed. This can happen if they get stuck between a piece of clothing and the victim's skin or when carelessly picking up tools, bundles of grain etc.
Risk
A Latrodectus bite is not always noticed. Latrodectism, the term for the typical symptoms of envenoming caused by these spiders, can occur in warm to tropical regions on all continents. Epidemic-like occurrences of envenoming are associated with periodic mass reproduction of these spiders, the causes of which are probably associated with climatic factors.
Accidents with species living in the wild such as L. tredecimguttatus, L. indistinctus or L. mactans most commonly occur during farming work in grain or cotton fields or in vineyards. However, accidents may also occur in other situations in which humans enter the natural distribution areas of these spiders, e.g. while camping or during military manoeuvres. L. mactans bites in outdoor toilets are not uncommon.
In countries where there are mainly species that live in the wild, the incidence of bites is highest during the summer months. In the regions where there are species that live in human habitations, accidents may occur throughout the year. In a study of 45 Latrodectus bites in South Africa that were treated over a period of 4 years, 30 were caused by L. indistinctus and 15 by L. geometricus. It was apparent from this study that envenoming caused by L. indistinctus was markedly more severe than that caused by L. geometricus, which only led to mild symptoms and signs of envenoming (Müller 1993).
There are occasional reports of the danger of spiders from the genus Steatoda (also part of the Theridiidae family) (Maretic 1978b). One case of envenoming due to Steatoda nobilis was documented in England (Warrell et al. 1991). This species, originally native to the Canary Islands, appears to be establishing itself in the south of England.
Literature (biological)
Abalos and Baez 1967, Aguilera et al. 2019, Bellmann 2001, Bettini 1964, Kaston 1970, Levi 1959, 1966, Maretic 1978a, 1979, Martindale and Newlands 1982, Raven and Gallon 1987b, Shulov 1966, Rueda et al. 2021, Sutherland 1983, Valdez-Mondragón and Cabrera-Espinosa 2023, Wright et al. 2019