Redback spider

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Redback spider
Female redback spider
Male redback spider
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Araneae
Family: Theridiidae
Genus: Latrodectus
Species: L. hasseltii
Binomial name
Latrodectus hasseltii
Thorell, 1870

The redback spider (Latrodectus hasseltii)[1] is a dangerous spider endemic to Australia. It is a member of the genus Latrodectus, the widow spiders, which are found throughout the world. The female is easily recognisable by her black body with a prominent red stripe on the upper side (i.e. the back) of her abdomen. Females have a body length of about a centimetre, while the male is smaller, being only 3 to 4 mm long. The redback spider is one of few arachnids which usually display sexual cannibalism while mating.

Redbacks are one of the most dangerous species of spiders in Australia.[2] Its neurotoxic venom is toxic to humans, with bites causing severe pain, often for over 24 hours. An antivenom is commercially available, and since its introduction in 1956, no deaths directly due to redback bites have been formally recorded.[3]

Contents

Taxonomy [edit]

The Redback spider is a member of the spider genus Latrodectus, in the family Theridiidae. It is related to the best-known member of the group, the black widow spider (Latrodectus mactans), found in North America and other regions. The closest relative of the redback is the katipo (Latrodectus katipo), which is native to New Zealand.[4] The common name of "redback" is derived from its distinctive red stripe along the dorsal aspect of its abdomen. Other common names include jockey spider, Murra-ngura spider, Kapara spider and the Kanna-jeri spider.[5]

The species was named in honour of A.W.M. van Hasselt, a colleague of the author Tamerlan Thorell, who described it in 1870.[6][7]

Physical description [edit]

The distinctive red stripe of the Australian redback spider
A young Australian redback spider, showing the white banding typical of a juvenile

The female redback has a round body about the size of a large pea (1 cm long), with long, slender legs. The body is a deep black colour (occasionally brownish), often containing an obvious orange to red longitudinal stripe on the upper abdomen. The stripe is sometimes broken or looks like small red dots. On the underside of the abdomen is an "hourglass"-shaped red/orange spot. Juvenile spiders have additional white markings on the abdomen. The male redback is three to four millimetres long and is light brown in colour, with white markings on the upper side of the abdomen and a pale hourglass marking on the underside.[8]

Ecology and behaviour [edit]

Web [edit]

Redback spider sitting in its web
Redback spider hauling a lizard into lair

The redback web is a disorganised, irregular tangle of fine but strong silk. The rear portion of the web forms a funnel-like retreat area where the spider and egg sacs are found. This area has vertical, sticky catching threads that run to ground attachments.[8][9] The vertical strands serve two purposes, it snares prey and small insects and can be potentially lifted in the air like a bungee cord, and secondly acts as a trip wire to alert the spider to the presence of prey or threats.

Prey [edit]

Redbacks usually prey on insects, but can capture larger animals that become entangled in the web, including king crickets, trapdoor spiders, and small lizards.[10] Commonly, prey-stealing occurs where larger females take food items stored in other spiders' webs.[8]

Life cycle [edit]

Male spiders mature in 37 to 167 days (average is about 90 days). Females mature in 60 to 325 days (average is about four months). Males live for up to six or seven months, while female may live between two and three years. Even without food, spiders may survive for an average of 100 days,[10] and sometimes over 300 days.[11]

Redbacks can survive temperatures from below freezing point to 40°C. [11] Although in desert areas of the Northern Territory, they survive temperatures exceeding 50°C for up to 12 hours a day.

Parasitoid [edit]

Agenioideus nigricornis, a spider wasp, is a parasitoid of the redback.[12]

Reproduction [edit]

Female redback guarding egg sac, note the male at left (circled)

The redback spider is one of only two animals to date where the male has been found to actively assist the female in sexual cannibalism. In the process of mating, the much smaller male somersaults to place his abdomen over the female's mouthparts. In about two of three cases, the female fully consumes the male while mating continues. Males which are not eaten die of their injuries soon after mating.[13]

Sacrifice during mating is thought to confer two advantages to the males. The first is the eating process allows for a longer period of copulation and thus fertilisation of more eggs. The second is females which have eaten a male are more likely to reject subsequent males.[14] Although this prohibits the possibility of future mating for the males, this is not a serious disadvantage, because the spiders are sufficiently sparse that only 20% of males ever find a potential mate during their lifetimes.[15]

Some redback males have been observed using an alternative tactic that also ensures more of their genetic material is passed on. Juvenile female redbacks nearing their final moulting and adulthood have fully formed reproductive organs, but lack openings in the exoskeleton that allow access to the organs. Males will bite through the exoskeleton and deliver sperm to the organs without performing the somersault seen in males mating with adult females. The females then moult within a few days and deliver a normal clutch of eggs.[16]

Once the female has mated, she can store sperm and use it over a period of up to two years to lay several batches of eggs. A female spider may lay eggs every 25 to 30 days. A single female normally lays between 40 and 300 eggs in each sac, but can lay up to 5000 eggs. The eggs hatch 13 to 15 days after being laid. Young redback spiders leave the maternal web by being carried on the wind. The spider extends its abdomen high in the air and produces a droplet of silk. The liquid silk is drawn out into a long gossamer thread that, when long enough, carries the spider away. Eventually, the silken thread will adhere to an object where the young spider will establish its own web.[10]

Distribution [edit]

Its origins are uncertain, and it may have been spread by human activities. The species was known by 1850 in South Australia, only 14 years after European settlement there, but was not reported in early spider collections in other colonies.[11] Redback spiders are now found in all but the most inhospitable environments in Australia and its cities. The redback spider is commonly found in close proximity to human residences. Webs are usually built in dry, sheltered sites, such as among rocks, in logs, shrubs, old tyres, sheds, outhouses, children's toys or under rubbish or litter.[8]

Introductions [edit]

Media in Japan have reported the discovery of redback spiders in Osaka, Japan,[11] within a hundred kilometres of Kansai International Airport. They are thought to have arrived in Japan by "hitching" a ride on the outside of airliners, or carried in cargoes of wood chips.[17] In 2008, redback spiders were found in Fukuoka, Japan. Over 700 have been found near the container terminal in Hakata Bay, Fukuoka City.[citation needed] In September 2012, a woman was hospitalised after being bitten by one in the Higashi Ward of Fukuoka City.[18] Warning signs about redback spiders have been posted in parks around the city, as Japan has had no dangerous venomous spiders before now.[citation needed] This has led to confusion in Japan, since the native spider Latrodectus elegans is also commonly known as the redback spider.[citation needed]

Redback spiders are also found in small colonies in areas of New Zealand. They are frequently intercepted by quarantine authorities, often amongst steel or car shipments.[11] They are found around Central Otago (including Alexandra, Bannockburn and near Wanaka)[11] in the South Island and New Plymouth in the North Island.[19]

Colonies have also been established in greenhouses in Belgium, and isolated observations indicate a possible presence in New Guinea, the Philippines, and India.[11] Some redbacks were found in Preston, Lancashire, UK after a container of parts arrived from Australia; some may have escaped into the countryside before pest controllers could destroy them.[20]

Tourist guides in the UAE warn visitors of redback spiders.[21]

Toxicology [edit]

Venom is produced by glands in the cephalothorax, and expelled venom travels through paired ducts from the cephalothorax, exiting through the tip of the spider's hollow fangs. The venom of the redback spider is thought to be similar to other Latrodectus spiders, and contains a number of high-molecular-weight proteins, one of which, alpha-latrotoxin (a neurotoxin), is active in humans. In vertebrates, alpha-latrotoxin produces its effect through destabilization of cell membranes and degranulation of nerve terminals, resulting in the release of neurotransmitters; it causes uncontrolled release of acetylcholine, norepinephrine, and GABA. The release of these neurotransmitters leads to the clinical manifestations of envenomation.[22] At concentrations of 200 ng/ml, the venom also deforms human red blood cells, an effect common to the venom of bees, the blue-ringed octupus, and a range of snakes.[23]

Bites in humans [edit]

Redback spider bites rarely cause significant morbidity, and deaths are even more rare.[24] Throughout Australian history, only 14 deaths from redbacks have been recorded.[25][26] A significant proportion of bites will not result in envenomation or any symptoms developing. Hundreds[11] or even thousands of people are thought to be bitten each year across Australia, although only about 20% of bite victims require treatment.[27] Children, the elderly, or those with serious medical conditions are at much higher risk of severe side effects and death resulting from a bite. No deaths have been reported since the introduction of antivenom in 1956.[3]

In an Australian study of 750 emergency hospital admissions for spider bites where the spider was definitively identified, 56 were from redbacks. Of these, 37 had significant pain lasting over 24 hours, but only six were treated with the antivenom.[28]

The larger female spider is responsible for almost all cases of redback spider bites in humans. The smaller male spider was thought to be unable to envenomate a human, although male bites have been reported. The rarity of male bite reports is probably due to the male's smaller size and proportionally smaller fangs, rather than the male being incapable of biting or lacking venom of potency similar to the female's. Cases have shown the male bite usually only produces short-lived, mild pain.[24]

Most bites occur in the warmer months between December and April, in the afternoon or evening.[24][29] As the female redback is slow-moving, and rarely leaves its web, bites generally occur as a result of a person placing a hand or other body part too close to the web, such as when reaching into dark holes or wall cavities. Bites can also occur if a spider has hidden in clothes or shoes.[22]

Symptoms [edit]

Bites from redback spiders produce a syndrome known as latrodectism, with symptoms similar to bites from other Latrodectus spiders. The syndrome is generally characterised by extreme pain and severe swelling.[30] The bite may be painful from the start, but sometimes only feels like a pinprick or mild burning sensation. Within an hour, victims generally develop more severe local pain with local swelling and sometimes piloerection (goosebumps). Pain, swelling and redness spread proximally from the site. Systemic envenoming is heralded by swollen or tender regional lymph nodes; associated features include malaise, nausea, vomiting, abdominal or chest pain, generalised sweating, headache, fever, hypertension and tremor.[22][24] Rare complications include seizure, coma, pulmonary edema, respiratory failure or localised skin infection.[29] Severe pain can persist for over 24 hours after being bitten.[28]

Treatment [edit]

Medical advice is recommended after being bitten by a redback spider. Usually, this requires observation in or near a medical facility for six hours from time of the bite.[22] Treatment is based on the severity of the bite; patients with localised pain, swelling and redness usually do not require any specific treatment apart from applying ice and routine analgesics. In more severe bites, the definitive treatment consists of administering redback antivenom, which will usually relieve symptoms of systemic envenoming immediately.

Antivenom is indicated in anyone suffering symptoms consistent with Latrodectus envenoming. Particular indications for using antivenom are:

  • Pain and swelling spreading proximally from site
  • Chest pain
  • Abdominal pain
  • Unusual sweating

Currently, this antivenom is recommended to be given intramuscularly(IM) rather than intravenously(IV), although some have suggested IM antivenom is not as effective as IV antivenom,[24][31] because IM antivenom takes longer to reach the blood serum.[32] Adverse reactions to redback antivenom are rare.[33] Antivenom may be effective for up to 3 months after a bite,[34] but in the vast majority of cases, it is administered within 24 hours.[29] Doses are the same for both children and adults.

In popular culture [edit]

Slim Newton popularised redbacks in his song "Redback on the toilet seat", which won the Golden Guitar at the first Country Music Awards of Australia in 1973.[35][36]

The Angels' 2006 album Red Back Fever described sightings of hand sized red back spiders in outback Australia near Pine Gap

Matilda Bay Brewing Company produces a wheat beer called Redback, with the distinctive red stripe as the logo.

The South Australia cricket team is nicknamed the Southern Redbacks and known as the West End Redbacks due to its sponsorship agreement with South Australian brewer, West End.

See also [edit]

References [edit]

  1. ^ Vink CJ, Sirvid PJ, Malumbres-Olarte J, Griffiths JW, Paquin P, Paterson AM (2008). "Species status and conservation issues of New Zealand’s endemic Latrodectus spider species (Araneae : Theridiidae)". Invertebr Syst 22 (6): 589–604. doi:10.1071/IS08027. 
  2. ^ Dangerous Spiders, Australian Museum web site
  3. ^ a b Wiener S (2003). "Latrodectism: a prospective cohort study of bites by formally identified Redback spiders". Med J Aust 179 (8): 455; author 455–6. PMID 14558881. 
  4. ^ http://australianmuseum.net.au/Redback-Spider/
  5. ^ Platnick N, Merrett p, Brignoli PM, ed. (1990). Advances in spider taxonomy, 1981-1987. A supplement to Brignoli’s "a catalogue of the Araneae described between 1940-1981. Manchester University Press. ISBN 0-7190-2782-9. 
  6. ^ Australian Biological Resources Study. "Species bank: Latrodectus hasseltii". Retrieved 2007-01-27. 
  7. ^ Thorell, T. 1870. Araneae nonnullae Novae Hollandie, descriptae. Öfvers. Kongl. vet. Akad. Förh. 27: 367-389. [369]
  8. ^ a b c d Australian Museum. "Redback Spider Fact Sheet". Retrieved 2007-02-18. 
  9. ^ Queensland Museum. "Identifying the Redback". Retrieved 2007-02-18. 
  10. ^ a b c Queensland Museum. "Redback Habitat and Life Cycle". Retrieved 2007-02-18. 
  11. ^ a b c d e f g h Vink, C. J.; Derraik, J. G. B.; Phillips, C. B.; Sirvid, P. J. (2010). "The invasive Australian redback spider, Latrodectus hasseltii Thorell 1870 (Araneae: Theridiidae): Current and potential distributions, and likely impacts". Biological Invasions 13 (4): 1003. doi:10.1007/s10530-010-9885-6.  edit
  12. ^ Krogmann, Lars; Austin, Andrew D (2011). "Systematics of Australian Agenioideus Ashmead (Hymenoptera: Pompilidae) with the first record of a spider wasp parasitizing Latrodectus hasselti Thorell (redback spider).". Australian Journal of Entomology. doi:10.1111/j.1440-6055.2011.00850.x. 
  13. ^ Forster, L. M. (1992). "The Stereotyped Behavior of Sexual Cannibalism in Latrodectus-Hasselti Thorell (Araneae, Theridiidae), the Australian Redback Spider". Australian Journal of Zoology 40: 1. doi:10.1071/ZO9920001.  edit
  14. ^ Andrade, Maydianne C. B. (5 January 1996). "Sexual Selection for Male Sacrifice in the Australian Redback Spider" (PDF). Science 271 (5245): 70–2. Bibcode:1996Sci...271...70A. doi:10.1126/science.271.5245.70. Retrieved 2011-04-18. 
  15. ^ Andrade, M. C. B. (2003). "Risky mate search and male self-sacrifice in redback spiders". Behavioral Ecology 14 (4): 531. doi:10.1093/beheco/arg015.  edit
  16. ^ Biaggio, M.D., and M.C.B. Andrade (12–16 August 2006). "Breaking an entry: Male Redback spiders inseminate juvenile females by ripping through their exoskeleton". Animal Behaviour Society meeting.
  17. ^ Victoria Museum. "Redback Spider". Retrieved 2007-02-18. 
  18. ^ Fukuoka Now magazine. "Woman Bitten by Deadly Redback Spider". Retrieved 6 September 2012. 
  19. ^ Reed C, Newland S, Downs, J, Forbes V, Gilbert S (September 2002). MAF Biosecurity Pest Risk Assessment: Spiders Associated With Table Grapes From United States of America (State of California), Australia, Mexico and Chile (PDF). MAF Biosecurity. Retrieved 2007-02-18. 
  20. ^ Metro. "Deadly Australian spiders 'invading' the UK, one field at a time". Retrieved 2010-06-24. 
  21. ^ http://archive.gulfnews.com/nation/General/10318145.html
  22. ^ a b c d Meier J, White J, ed. (1995). Handbook of clinical toxicology of animal venoms and poisons. CRC Press. ISBN 0-8493-4489-1. 
  23. ^ Flachsenberger, W.; Leigh, C. M.; Mirtschin, P. J. (1995). "Sphero-echinocytosis of human red blood cells caused by snake, red-back spider, bee and blue-ringed octopus venoms and its inhibition by snake sera". Toxicon 33 (6): 791–797. doi:10.1016/0041-0101(95)00014-D. PMID 7676470.  edit
  24. ^ a b c d e Isbister G, Gray M (2003). "Latrodectism: a prospective cohort study of bites by formally identified Redback spiders". Med J Aust 179 (2): 88–91. PMID 12864719. 
  25. ^ http://www.avru.org/compendium/biogs/A000006b.htm Australian Venom Research Unit - Redback Spiders
  26. ^ Carol Booth (2009). "Along Came A Spider". Australian Geographic.  http://www.australiangeographic.com.au/journal/along-came-a-spider.htm
  27. ^ White J (1998). "Envenoming and antivenom use in Australia". Toxicon 36 (11): 1483–92. doi:10.1016/S0041-0101(98)00138-X. PMID 9792162. 
  28. ^ a b Isbister, G. K.; Gray, M. R. (2002). "A prospective study of 750 definite spider bites, with expert spider identification". QJM 95 (11): 723–731. doi:10.1093/qjmed/95.11.723. PMID 12391384.  edit
  29. ^ a b c Sutherland S, Trinca J (1978). "Survey of 2144 cases of Redback spider bites: Australia and New Zealand, 1963--1976". Med J Aust 2 (14): 620–3. PMID 732670. 
  30. ^ Redback Spider Facts
  31. ^ Isbister G (2002). "Failure of intramuscular antivenom in Redback spider envenoming". Emerg Med (Fremantle) 14 (4): 436–9. doi:10.1046/j.1442-2026.2002.00356.x. PMID 12534488. 
  32. ^ Isbister, G. K.; O'Leary, M.; Miller, M.; Brown, S. G. A.; Ramasamy, S.; James, R.; Schneider, J. S. (2008). "A comparison of serum antivenom concentrations after intravenous and intramuscular administration of redback (widow) spider antivenom". British Journal of Clinical Pharmacology 65 (1): 139–143. doi:10.1111/j.1365-2125.2007.03004.x. PMC 2291270. PMID 18171334.  edit
  33. ^ White J. "CSL antivenom handbook". Retrieved 2007-02-18. 
  34. ^ Banham N, Jelinek G, Finch P (1994). "Late treatment with antivenom in prolonged Redback spider envenomation". Med J Aust 161 (6): 379–81. PMID 8090117. 
  35. ^ "Slim Newton". countrymusic.com.au. 1998. 
  36. ^ "Bellbird Music". countrymusic.com.au. 2009. 

External links [edit]

Media related to Latrodectus hasselti at Wikimedia Commons Data related to Latrodectus hasselti at Wikispecies

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