Red-back spider
Encyclopedia
The Redback spider is a potentially dangerous spider
endemic to Australia
. It is a member of the genus Latrodectus, or widow family of 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 millimetres long. The Redback spider is one of few arachnids which display sexual cannibalism
while mating.
Redbacks are considered one of the most dangerous spiders in Australia. The Redback spider has a neurotoxic venom which is toxic to humans with bites causing severe pain. There is an antivenom for Redback bites which is commercially available.
. It is related to the best known member of the group, the black widow spider (Latrodectus mactans), found in North America
and other regions. Close relatives of the Redback are the katipo (Latrodectus katipo), which is native to New Zealand
. 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.
The species was named in honour of A.W.M. van Hasselt, a colleague of the author Tamerlan Thorell
, who described it in 1870.
The female Redback has a round body about the size of a large pea (1 centimetre 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 there 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 hour-glass marking on the underside.
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. The vertical strands serve two purposes, it snares prey and small insects 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.
s. Commonly prey stealing occurs where larger females take food items stored in other spiders' webs. Most commonly, ants stray into the web. Redback spiders are known for deadly poison and lightning speed.
. In the process of mating, the much smaller male somersaults to place his abdomen over the female's mouthparts. In about 2 out of 3 cases, the female consumes the male while mating continues. Males who are not eaten die soon after mating.
Males who sacrifice themselves during mating present two advantages over males who do not. The first is that males who are eaten are able to copulate for a longer period and thus fertilise more eggs. The second is that females who have eaten a male are more likely to reject subsequent males.
Some Redback males have been observed utilising an alternative tactic that also ensures that more of their genetic material is passed on. Juvenile female Redbacks who are 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.
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.
Its origins are uncertain, and it may have been spread by human activities during the 19th century. 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.
The wide distribution range of the related species Latrodectus geometricus
, the brown widow, includes Brisbane
, Australia.
, Japan within a hundred kilometres of Kansai International Airport
. It was speculated that they arrived in Japan by "hitching" a ride on the outside of airliners, or carried in cargoes of wood chips.
In 2008, Redback spiders were found in Fukuoka, Japan. Over 700 have been found near the container terminal in Hakata Bay, Fukuoka city. Warning signs about Redback spiders have been posted in parks around the city as Japan has had no dangerous venomous spiders before now. This has led to confusion in Japan since the native spider Latrodectus elegans is also commonly known as the redback spider.
Redback spiders are also found in small colonies in areas of New Zealand. These spiders were imported on Australian hardwood poles used for electric power and telephone. They are found around Central Otago
in the South Island and New Plymouth
in the North Island.
Tourist Guides in UAE warn visitors of Redback spiders.
Redback Spiders have been found in the UK after a container of parts from Australia
arrived in Preston, Lancashire
; some may have escaped into the countryside before pest controllers could destroy them.
(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 neuro-transmitters; it causes uncontrolled release of the neurotransmitters acetylcholine
, Norepinephrine
, and GABA
. The release of these neurotransmitters leads to the clinical manifestations of envenomation.
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 that the male bite usually only produces short-lived, mild pain.
Most bites occur in the warmer months between December and April and in the afternoon or evening. 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.
, with symptoms similar to bites from other Latrodectus spiders. The syndrome is generally characterised by extreme pain and severe swelling. 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
. Rare complications include seizure, coma, pulmonary edema, respiratory failure or localised skin infection. Severe pain can persist for over 24 hours after being bitten.
s. 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:
Currently it is recommended that this antivenom be given intramuscularly(IM) rather than intravenously(IV), although some have suggested that IM antivenom is not as effective as IV antivenom. Adverse reactions to Redback antivenom are rare. Antivenom may be effective for up to 3 months after a bite. Doses are the same for both children and adults.
Spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
endemic to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. It is a member of the genus Latrodectus, or widow family of 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 millimetres long. The Redback spider is one of few arachnids which display sexual cannibalism
Sexual cannibalism
Sexual cannibalism is a special case of cannibalism in which a female organism kills and consumes a male of the same species before, during, or after copulation. On rare occasions, these roles are reversed.-Prevalence:...
while mating.
Redbacks are considered one of the most dangerous spiders in Australia. The Redback spider has a neurotoxic venom which is toxic to humans with bites causing severe pain. There is an antivenom for Redback bites which is commercially available.
Taxonomy
The Redback spider is a member of the spider genus Latrodectus, in the family TheridiidaeTheridiidae
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world...
. It is related to the best known member of the group, the black widow spider (Latrodectus mactans), found in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and other regions. Close relatives of the Redback are the katipo (Latrodectus katipo), which is native to New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. 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.
The species was named in honour of A.W.M. van Hasselt, a colleague of the author Tamerlan Thorell
Tamerlan Thorell
Tord Tamerlan Teodor Thorell was a Swedish arachnologist.Thorell studied spiders with Giacomo Doria at the Museo Civico di Storia Naturale de Genoa...
, who described it in 1870.
Physical description
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
. The stripe is sometimes broken or looks like small red dots. On the underside of the abdomen there 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 hour-glass marking on the underside.
Web
Bungee cord
A bungee cord , also known as a shock cord, is an elastic cord composed of one or more elastic strands forming a core, usually covered in a woven cotton or polypropylene sheath...
, and secondly acts as a trip wire to alert the spider to the presence of prey.
Prey
Redbacks usually prey on insects but they can capture larger animals that become entangled in the web including king crickets, trapdoor spiders, and small lizardLizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s. Commonly prey stealing occurs where larger females take food items stored in other spiders' webs. Most commonly, ants stray into the web. Redback spiders are known for deadly poison and lightning speed.
Life cycle
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 6 or 7 months while female may live for between 2 and 3 years. Even without food spiders may survive for an average of 100 days.Reproduction
The Redback spider is one of only two animals to date where the male has been found to actively assist the female in sexual cannibalismSexual cannibalism
Sexual cannibalism is a special case of cannibalism in which a female organism kills and consumes a male of the same species before, during, or after copulation. On rare occasions, these roles are reversed.-Prevalence:...
. In the process of mating, the much smaller male somersaults to place his abdomen over the female's mouthparts. In about 2 out of 3 cases, the female consumes the male while mating continues. Males who are not eaten die soon after mating.
Males who sacrifice themselves during mating present two advantages over males who do not. The first is that males who are eaten are able to copulate for a longer period and thus fertilise more eggs. The second is that females who have eaten a male are more likely to reject subsequent males.
Some Redback males have been observed utilising an alternative tactic that also ensures that more of their genetic material is passed on. Juvenile female Redbacks who are 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.
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
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...
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.
Distribution
The wide distribution range of the related species Latrodectus geometricus
Latrodectus geometricus
The spider Latrodectus geometricus, commonly known as the brown widow, grey widow, or geometric button spider, is one of the widow spiders in the genus Latrodectus. As such, it is a "cousin" to the more famous Latrodectus mactans...
, the brown widow, includes Brisbane
Brisbane
Brisbane is the capital and most populous city in the Australian state of Queensland and the third most populous city in Australia. Brisbane's metropolitan area has a population of over 2 million, and the South East Queensland urban conurbation, centred around Brisbane, encompasses a population of...
, Australia.
Introductions
Media in Japan have reported the discovery of Redback spiders in OsakaOsaka
is a city in the Kansai region of Japan's main island of Honshu, a designated city under the Local Autonomy Law, the capital city of Osaka Prefecture and also the biggest part of Keihanshin area, which is represented by three major cities of Japan, Kyoto, Osaka and Kobe...
, Japan within a hundred kilometres of Kansai International Airport
Kansai International Airport
is an international airport located on an artificial island in the middle of Osaka Bay, southwest of Ōsaka Station, located within three municipalities, including Izumisano , Sennan , and Tajiri , in Osaka Prefecture, Japan. The airport is off the Honshu shore. The airport serves as an...
. It was speculated that they arrived in Japan by "hitching" a ride on the outside of airliners, or carried in cargoes of wood chips.
In 2008, Redback spiders were found in Fukuoka, Japan. Over 700 have been found near the container terminal in Hakata Bay, Fukuoka city. Warning signs about Redback spiders have been posted in parks around the city as Japan has had no dangerous venomous spiders before now. This has led to confusion in Japan since the native spider Latrodectus elegans is also commonly known as the redback spider.
Redback spiders are also found in small colonies in areas of New Zealand. These spiders were imported on Australian hardwood poles used for electric power and telephone. They are found around Central Otago
Otago
Otago is a region of New Zealand in the south of the South Island. The region covers an area of approximately making it the country's second largest region. The population of Otago is...
in the South Island and New Plymouth
New Plymouth
New Plymouth is the major city of the Taranaki Region on the west coast of the North Island of New Zealand. It is named after Plymouth, Devon, England, from where the first English settlers migrated....
in the North Island.
Tourist Guides in UAE warn visitors of Redback spiders.
Redback Spiders have been found in the UK after a container of parts from Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
arrived in Preston, Lancashire
Lancashire
Lancashire is a non-metropolitan county of historic origin in the North West of England. It takes its name from the city of Lancaster, and is sometimes known as the County of Lancaster. Although Lancaster is still considered to be the county town, Lancashire County Council is based in Preston...
; some may have escaped into the countryside before pest controllers could destroy them.
Toxicology
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-latrotoxinAlpha-latrotoxin
α-Latrotoxin can naturally be found in widow spiders of the genus Latrodectus. The most famous of those spiders are the black widows, Latrodectus mactans. The venom of widow spiders contains several protein toxins, called latrotoxins, which selectively target against either vertebrates, insects...
(a neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
), 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 neuro-transmitters; it causes uncontrolled release of the neurotransmitters acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
, Norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
, and GABA
Gamma-aminobutyric acid
γ-Aminobutyric acid is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system...
. The release of these neurotransmitters leads to the clinical manifestations of envenomation.
Bites in humans
Redback spider bites rarely cause significant morbidity, and deaths are even more rare. Throughout Australian history, only 14 deaths from redbacks have been recorded. A significant proportion of bites will not result in envenomation or any symptoms developing. It is believed that thousands of people are bitten each year across Australia, although only about 20% of bite victims require treatment. Children and 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.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 that the male bite usually only produces short-lived, mild pain.
Most bites occur in the warmer months between December and April and in the afternoon or evening. 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.
Symptoms
Bites from Redback spiders produce a syndrome known as latrodectismLatrodectism
Latrodectism is the clinical syndrome caused by the neurotoxic venom , that can be injected by the bite of any spider that is a member of the spider genus Latrodectus, in the family Theridiidae....
, with symptoms similar to bites from other Latrodectus spiders. The syndrome is generally characterised by extreme pain and severe swelling. 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
Malaise
Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...
, nausea, vomiting, abdominal or chest pain, generalised sweating, headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
, fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
and tremor
Tremor
A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving to-and-fro movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, face, head, vocal folds, trunk, and legs. Most tremors occur in the...
. Rare complications include seizure, coma, pulmonary edema, respiratory failure or localised skin infection. Severe pain can persist for over 24 hours after being bitten.
Treatment
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. 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 analgesicAnalgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
s. 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 it is recommended that this antivenom be given intramuscularly(IM) rather than intravenously(IV), although some have suggested that IM antivenom is not as effective as IV antivenom. Adverse reactions to Redback antivenom are rare. Antivenom may be effective for up to 3 months after a bite. Doses are the same for both children and adults.
External links
- Australian Museum
- Rochedale State School
- Queensland Museum
- University of Toronto
- Description, distribution, pictures (Australian Government: Department of the Environment and Heritage)
- Spinnenkenners vrezen dat er toch dodelijke Redbacks in Bree overleven (Belgian Redbacks in Bree, in Dutch)