Latrodectus - wikipedia Latrodectus Latrodectus Scientific classification Kingdom : Animalia Phylum : Arthropoda Subphylum : Chelicerata Class : Arachnida Order : Araneae Infraorder : Araneomorphae Family : Theridiidae Genus : Latrodectus Walckenaer, 1805 Species 31 described species, estimated 65 species living Latrodectus is a genus of spiders in the family Theridiidae, most of which are commonly known as widow spiders. The genus contains 31 recognized species distributed worldwide, including the North American black widows ( L. mactans, L. hesperus, and L. variolus ), the button spiders of Africa, and the Australian redback spider. Species vary widely in size. In most cases, the females are dark - coloured and readily identifiable by reddish markings on the abdomen, which are often ( but not always ) hourglass - shaped. The venomous bite of these spiders is considered particularly dangerous because of the neurotoxin latrotoxin, which causes the condition latrodectism, both named after the genus. The female black widow has unusually large venom glands and its bite can be particularly harmful to humans. However, despite the genus ' notoriety, Latrodectus bites are rarely fatal. Only female bites are dangerous to humans. Contents 1 Description 2 Behavior 3 Taxonomy 3.1 Species 4 Distribution 5 Bite 6 See also 7 References 8 Further reading 9 External links Description Female widow spiders are typically dark brown or a shiny black in colour when they are full grown, usually exhibiting a red or orange hourglass on the ventral surface ( underside ) of the abdomen ; some may have a pair of red spots or have no marking at all. The male widow spiders often exhibit various red or red and white markings on the dorsal surface ( upper side ) of the abdomen, ranging from a single stripe to bars or spots. Females of a few species are paler brown and some have no bright markings. The bodies of black widow spiders range from 3 -- 10 millimetres ( 0.12 -- 0.39 in ) in size ; some females can measure 13 millimetres ( 0.51 in ) in their body length. Behavior An atypical black widow spider, with multiple red spots on her back, and vaguely yellow stripes on her legs. The prevalence of sexual cannibalism, a behavior in which the female eats the male after mating, has inspired the common name `` widow spiders ''. This behaviour may promote the survival odds of the offspring ; however, females of some species only rarely show this behaviour, and much of the documented evidence for sexual cannibalism has been observed in laboratory cages where the males could not escape. Male black widow spiders tend to select their mates by determining if the female has eaten already to avoid being eaten themselves. They are able to tell if the female has fed by sensing chemicals in the web. Like other members of the family Theridiidae, widow spiders construct a web of irregular, tangled, sticky silken fibres. Black widow spiders prefer to nest near the ground in dark and undisturbed areas, usually in small holes produced by animals, or around construction openings or wood piles. Indoor nests are in dark, undisturbed places as well such as under desks or furniture or in a basement. The spider very frequently hangs upside down near the centre of its web and waits for insects to blunder in and get stuck. Then, before the insect can extricate itself, the spider rushes over to bite it and wrap it in silk. To feed, it uses its fangs to inject digestive enzymes, liquefying the prey 's internal organs. Their prey consists of small insects such as flies, mosquitoes, grasshoppers, beetles, and caterpillars. If the spider perceives a threat, it quickly lets itself down to the ground on a safety line of silk. As with other web - weavers, these spiders have very poor eyesight and depend on vibrations reaching them through their webs to find trapped prey or warn them of larger threats. When a widow spider is trapped, it is unlikely to bite, preferring to play dead or flick silk at the potential threat ; bites are the result of continual harassment. While some species are more aggressive, most are not ; many injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched. The ultimate tensile strength and other physical properties of Latrodectus hesperus ( western black widow ) silk were found to be similar to the properties of silk from orb - weaving spiders that had been tested in other studies. The tensile strength for the three kinds of silk measured in the Blackledge study was about 1,000 MPa. The ultimate strength reported in a previous study for Nephila edulis was 1,290 ± 160 MPa. The tensile strength of spider silk is comparable to that of steel wire of the same thickness. However, as the density of steel is about six times that of silk, silk is correspondingly stronger than steel wire of the same weight. Spiders of the genus Steatoda ( also of the Theridiidae family ) are often mistaken for widow spiders, and are known as `` false widow spiders '' ; they are significantly less harmful to humans. Taxonomy Male L. elegans from Japan L. hesperus hair and markings L. hesperus profile Ventral side of a L. geometricus displaying the hourglass marking Dorsal side of a L. geometricus in Colorado, US L. hesperus with egg sac L. tredecimguttatus ( female swollen with eggs ) The genus Latrodectus was erected by Walckenaer in 1805, for the species Latrodectus tredecimguttatus and Latrodectus mactans. Arachnologist Herbert Walter Levi revised the genus in 1959, studying the female sexual organs and noting their similarity across described species. He concluded the colour variations were variable across the world and were not sufficient to warrant species status, and reclassified the redback and several other species as subspecies of the black widow spider. Levi also noted that study of the genus had been contentious ; in 1902, both F.P Cambridge and Friedrich Dahl had revised the genus, with each criticising the other. Cambridge questioned Dahl 's separating species on what he considered minor anatomical details, and the latter dismissed the former as an `` ignoramus ''. Species As of July 2017, the World Spider Catalog accepted the following species : Latrodectus antheratus ( Badcock, 1932 ) -- Paraguay, Argentina Latrodectus apicalis Butler, 1877 -- Galapagos Is. Latrodectus bishopi Kaston, 1938 -- US Latrodectus cinctus Blackwall, 1865 -- Cape Verde Is., Africa, Kuwait, Iran Latrodectus corallinus Abalos, 1980 -- Argentina Latrodectus curacaviensis ( Müller, 1776 ) -- Lesser Antilles, South America Latrodectus dahli Levi, 1959 -- Morocco to Central Asia Latrodectus diaguita Carcavallo, 1960 -- Argentina Latrodectus elegans Thorell, 1898 -- India, Myanmar, China, Japan Latrodectus erythromelas Schmidt & Klaas, 1991 -- India, Sri Lanka Latrodectus geometricus C.L. Koch, 1841 -- Cosmopolitan Latrodectus hasselti Thorell, 1870 -- Southeast Asia to Australia, New Zealand Latrodectus hesperus Chamberlin & Ivie, 1935 -- North America, Israel Latrodectus hystrix Simon, 1890 -- Yemen, Socotra Latrodectus indistinctus O. Pickard - Cambridge, 1904 -- Namibia, South Africa Latrodectus karrooensis Smithers, 1944 -- South Africa Latrodectus katipo Powell, 1871 -- New Zealand Latrodectus lilianae Melic, 2000 -- Spain, Algeria Latrodectus mactans ( Fabricius, 1775 ) -- probably native to North America only ( introduced elsewhere ) Latrodectus menavodi Vinson, 1863 -- Madagascar, Comoro Is., Aldabra Latrodectus mirabilis ( Holmberg, 1876 ) -- Argentina Latrodectus obscurior Dahl, 1902 -- Cape Verde Is., Madagascar Latrodectus pallidus O. Pickard - Cambridge, 1872 -- Cape Verde Is., Libya to Central Asia Latrodectus quartus Abalos, 1980 -- Argentina Latrodectus renivulvatus Dahl, 1902 -- Africa, Saudi Arabia, Yemen, Iraq Latrodectus revivensis Shulov, 1948 -- Israel Latrodectus rhodesiensis Mackay, 1972 -- Southern Africa Latrodectus thoracicus Nicolet, 1849 -- Chile Latrodectus tredecimguttatus ( Rossi, 1790 ) ( type species ) -- Mediterranean to China Latrodectus variegatus Nicolet, 1849 -- Chile, Argentina Latrodectus variolus Walckenaer, 1837 -- US, Canada Distribution Widow spiders can be found on every continent of the world except Antarctica. In North America, the black widows commonly known as southern ( Latrodectus mactans ), western ( Latrodectus hesperus ), and northern ( Latrodectus variolus ) can be found in the United States, as well as parts of southern Canada -- particularly in the Okanagan Valley of British Columbia, as can the `` gray '' or `` brown widow spiders '' ( Latrodectus geometricus ) and the `` red widow spiders '' ( Latrodectus bishopi ). The blue mud dauber ( Chalybion californicum ) is a wasp that is the primary predator of black widow spiders. The most prevalent species occurring in Australia is commonly called the redback ( Latrodectus hasselti ). Bite Due to the presence of latrotoxin in their venom, black widow bites are potentially dangerous and may result in systemic effects ( latrodectism ) including severe muscle pain, abdominal cramps, hyperhidrosis, tachycardia, and muscle spasms. Symptoms usually last for 3 -- 7 days, but may persist for several weeks. Each year, about 2,200 people report being bitten by a black widow, but most recover within 24 hours with medical treatment ( male spiders produce the toxins to help with their own hunting, but they make such a diluted version that they are not harmful to most people ). Also, many people who are bitten develop few symptoms since the spider may not inject its venom. Black widows are not especially aggressive spiders, and they rarely bite humans unless startled or otherwise threatened. Contrary to popular belief, most people who are bitten suffer no serious damage, let alone death. Fatal bites were reported in the early - 20th century mostly with Latrodectus tredecimguttatus, the Mediterranean black widow. Since the venom is not likely to be life - threatening, antivenom has been used as pain relief and not to save lives. However, a study demonstrated that standardized pain medication, when combined with either antivenom or a placebo, had similar improvements in pain and resolution of symptoms. See also List of spiders associated with cutaneous reactions References ^ Jump up to : `` Gen. Latrodectus Walckenaer, 1805 '', World Spider Catalog, Natural History Museum Bern, retrieved 2016 - 01 - 28 ^ Jump up to : `` Species list for Latrodectus ''. World Spider Catalog. Natural History Museum Bern. Retrieved 2016 - 01 - 28. Jump up ^ `` Black Widow Spiders ''. Orkin Pest Control. Retrieved 19 June 2017. Jump up ^ Breene, R.G. ; Sweet, M.H. ( 1985 ). `` Evidence of insemination of multiple females by the male Black Widow Spider, Latrodectus mactans ( Araneae, Theridiidae ) '' ( PDF ). The Journal of Arachnology. 13 ( 3 ) : 331 -- 335. Jump up ^ `` Male spiders let females eat them for kids ' sake : Study ''. livescience. 23 December 2011. Retrieved 23 December 2011. Jump up ^ Johnson, J. Chadwick ; Trubl, Patricia ; Blackmore, Valerie ; Miles, Lindsay ( August 2011 ). `` Male black widows court well - fed females more than starved females : silken cues indicate sexual cannibalism risk ''. Animal Behaviour. 82 ( 2 ) : 383 -- 390. doi : 10.1016 / j. anbehav. 2011.05. 018. Jump up ^ Baruffaldi, Luciana ; Andrade, Maydianne C.B. ( April 2015 ). `` Contact pheromones mediate male preference in black widow spiders : avoidance of hungry sexual cannibals ? ''. Animal Behaviour. 102 : 25 -- 32. doi : 10.1016 / j. anbehav. 2015.01. 007. Jump up ^ `` Black Widow Spider - Facts, Bite & Habitat Information ''. Animal Corner. Retrieved 4 November 2016. ^ Jump up to : `` Black Widow Spiders ''. National Geographic. 10 September 2010. Retrieved 19 June 2017. Jump up ^ Nelsen, David ; Kelln, Wayne ; Hayes, William. `` Poke but do n't pinch : risk assessment and venom metering in the western black widow spider, Latrodectus hesperus ''. Animal Behaviour. 89 : 107 -- 114. doi : 10.1016 / j. anbehav. 2013.12. 019. Retrieved 12 October 2015. Jump up ^ Blackledge, T.A. ; Swindeman, John E. ; Hayashi, Cheryl Y. ( 15 May 2005 ). `` Quasistatic and continuous dynamic characterization of the mechanical properties of silk from the cobweb of the black widow spider Latrodectus hesperus '' ( PDF ). Journal of Experimental Biology. 208 ( 10 ) : 1937 -- 1949. doi : 10.1242 / jeb. 01597. Jump up ^ `` Astm a36 ''. OnlineMetals.com. Archived from the original on 9 May 2013. Jump up ^ Elices, Manuel ; Guinea, Gustavo V. ; Pérez - Rigueiro, José ; Plaza, Gustavo R. ; et al. ( 2005 ). `` Finding Inspiration in Argiope Trifasciata Spider Silk Fibers ''. JOM. 57 ( 2 ) : 60 -- 66. Bibcode : 2005JOM... 57b... 60E. doi : 10.1007 / s11837 - 005 - 0218 - 7. Retrieved 2009 - 01 - 23. Jump up ^ Walckenaer, C.A. ( 1805 ), Tableau des aranéides ou caractères essentiels des tribus, genres, familles et races que renferme le genre Aranea de Linné, avec la désignation des espèces comprises dans chacune de ces divisions, Paris : Dentu, pp. 81 -- 82 ^ Jump up to : Levi, Herbert W. ( 1959 ). `` The Spider Genus Latrodectus ( Araneae, Theridiidae ) ''. Transactions of the American Microscopical Society. 78 ( 1 ) : 7 -- 43. JSTOR 3223799. doi : 10.2307 / 3223799. Jump up ^ ( Preston - Malfham, 1998 ). Jump up ^ Drees, Bastiaan M. ; Jackman, John A. ( 1999 ). `` Mud Daubers ''. Field Guide to Texas Insects. Gulf Publishing Company. ISBN 978 - 0 - 87719 - 263 - 3. Archived from the original on 12 July 2007. Retrieved 10 July 2007. Jump up ^ Ushkaryov, YA ; Rohou, A ; Sugita, S ( 2008 ). `` alpha - Latrotoxin and its receptors ''. Handbook of experimental pharmacology. Handbook of Experimental Pharmacology. 184 ( 184 ) : 171 -- 206. ISBN 978 - 3 - 540 - 74804 - 5. PMC 2519134. PMID 18064415. doi : 10.1007 / 978 - 3 - 540 - 74805 - 2_7. Jump up ^ Peterson, ME ( November 2006 ). `` Black widow spider envenomation ''. Clinical techniques in small animal practice. 21 ( 4 ) : 187 -- 90. PMID 17265903. doi : 10.1053 / j. ctsap. 2006.10. 003. Jump up ^ Why Black Widow Spider Venom Is So Potent. By Jennifer Viegas, Discovery News January 6, 2015 Jump up ^ Bettini, S ( 1964 ). `` Epidemiology of latrodectism ''. Toxicon. 2 ( 2 ) : 93 -- 102. PMID 14301291. doi : 10.1016 / 0041 - 0101 ( 64 ) 90009 - 1. ^ Jump up to : Isbister, Geoffrey K. ; Page, Colin B. ; Buckley, Nicholas A. ; Fatovich, Daniel M. ; Pascu, Ovidiu ; MacDonald, Stephen P.J. ; Calver, Leonie A. ; Brown, Simon G.A. ( 2014 ). `` Randomized Controlled Trial of Intravenous Antivenom Versus Placebo for Latrodectism : The Second Redback Antivenom Evaluation ( RAVE - II ) Study ''. Annals of Emergency Medicine. 64 : 620 -- 8. e2. PMID 24999282. doi : 10.1016 / j. annemergmed. 2014.06. 006. ( Subscription required ( help ) ). Further reading Insects and Spiders. New York : St. Remy Media Inc. / Discovery Books. 2000. p. 35. Freeman, Scott ( 2003 ). Biological Science. Prentice - Hall. Hillyard, Paul ( 1994 ). The Book of Spiders. New York : Random House, Inc. pp. 47 -- 50. Hillyard, Paul ( 1994 ). The Book of the Spiders. New York : Avon Books. pp. 22 -- 35. Martin, Louise ( 1988 ). Black Widow Spiders. Rourke Enterprises, Inc. pp. 18 -- 20. Preston - Malfham, Ken ( 1998 ). Spiders. Edison, New Jersey : Chartwell Books. p. 40. `` Arthropod ''. Microsoft Encarta Online Encyclopedia. 2004. Abalos, J.W. ( 1962 ). `` The egg - sac in the Identification of Species of Latrodectus ( Black - Widow Spiders ) '' ( PDF ). Retrieved September 26, 2013. Levi, H.W. ; McCrone, J.D. ( 1964 ). `` North American Widow Spiders of the Latrodectus curacaviensis Group ''. External links Media related to Latrodectus at Wikimedia Commons Data related to Latrodectus at Wikispecies Tree of Life : Latrodectus Black Widow Spider : Large format photographs and information Description of crossing experiments between various Latrodectus species widow spider parasitoids on the UF / IFAS Featured Creatures Web site Taxon identifiers Wd : Q385932 ADW : Latrodectus BugGuide : 1999 GBIF : 2157920 iNaturalist : 47370 ITIS : 848644 NCBI : 6923 WSC : urn : lsid : nmbe.ch : spidersp : 007816 World Spider Catalog : 00702 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Latrodectus&oldid=804408983 '' Categories : Latrodectus Spider genera Venomous spiders Cosmopolitan spiders Hidden categories : Pages containing links to subscription - only content All articles with unsourced statements Articles with unsourced statements from January 2016 Articles with ' species ' microformats All articles with failed verification Articles with failed verification from June 2017 Articles containing potentially dated statements from July 2017 All articles containing potentially dated statements Talk Contents About Wikipedia Wikispecies Afrikaans Български Brezhoneg Català Cebuano Deutsch Español Esperanto Euskara فارسی Français Gaeilge 한국어 Hrvatski Italiano עברית ಕನ್ನಡ Magyar Македонски Nederlands Norsk ਪੰਜਾਬੀ Polski Português Română Русский Simple English Sranantongo Suomi Svenska ไทย Tiếng Việt Winaray Edit links This page was last edited on 8 October 2017, at 20 : 42. 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Question: where is the red marking on a black widow
Answer: the abdomen