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Oceania's most venomous spiders


Of the 35,000 species of spiders described worldwide (out of an estimated 170,000 species), only a handful are considered to be dangerous and only 27 are known to have caused human fatalities.

Though most people have a big fear of spiders, it seems that venomous spiders are not such a big threat to humans as many people believe.

First of all, studies have shown that most serious bites attributed to spiders were, in fact, due to other causes, notably other arthropods.
Secondly, antivenin against spider bite has become very effective and thus made the occurrence of death resulting from a spider's bite a very rare thing.
Lastly, spider venom, in general, is usually almost harmless to humans, since it evolved for capturing or killing small invertebrates and not big mammals like ourselves.

There are, however, a few exceptions, and bites from certain species can cause severe dermatological lesions and other symptoms which require urgent medical treatment and care.

On a worldwide basis, Australia and New Zealand appear to be home to more dangerous species of spiders than anywhere else. Indeed, a number of Australian spiders are highly venomous and some can, at least in theory, be deadly.

1. Widow Spiders, or Redback Spiders (Latrodectus)

- Redback Spider, Australian Redback Spider (Latrodectus hasselti)

Redback Spiders can be found everywhere in Australia, where they are very common, especially in the densely populated urban areas and in the warmer regions. An Australian beer is even named after this kind of popular species. Though this species is native to Australia, it has been imported to New Zealand and Southeast Asia.

Redbacks are often found near human habitations, notably in verandas, sheds, or storage yards, on industrial sites and even inside houses. They also hide in shelterd spots, holes, crevices, hollow logs, wood or junk piles.

The Redback Spider is related to the venomous Black Widow Spider and looks very similar. The only difference is that the Redback usually has a very distinctive red stripe (instead of an hourglass) on its back.

The female's body measures roughly 10 mm (4/10 inch). The male is tiny.

Redback webs are messy and very sticky and always seem to contain several egg sacks, white to creamy coloured oval blobs, 1 cm or bigger in size.

Redback Spiders feed mostly on insects, but will also catch prey as big as small lizards. They are known to steal wrapped prey from each other's webs.

The Redback's unique mating ritual almost always results in the death of the male. To attract Indeed, to attract the female's attention, the male displays himself as a prey by baring his abdomen. While he fertilizes the female, his partner is already busy squirting "digestive juices" onto his abdomen.

Only the bite of a female Redback Spider is toxic (the males are too small to bite anyway...).

The Redback hospitalizes almost 300 people every year. Yet, to be bitten, one must generally stick one's hand into its web, since it rarely leaves it. Besides, bites are ineffective because this species' fangs are tiny. Furthermore, this spider's venom is a very slow acting toxin, and most people don't show any reaction to it, except a bad itch.

The venom attacks the nervous system. And bites might cause a severe pain, accompanied by localized sweating at the bite site, and later on more sweating, muscle weakness, nausea, vomiting, headaches, and sometimes even paralysis.

A simple ice pack is the best first aid and often all that is required since many victims people don't develop any symptoms. However, when severe pain or other symptoms do develop, medical help should be sought. Nobody has died from a Redback Spider bite since antivenin has become available, in 1956.

Other Widow Spiders of Australia and Oceania are:

- Red Katipo (Latrodectus katipo): found in New Zealand.
- Brown Widow, Grey Widow, or Brown Button Spider (Latrodectus geometricus): a species of unclear origin, today found virtually worldwide, from Africa to the USA, South America and Australia.



2. Australian Funnel-Web Spiders

These 36 species of spiders belong to the family Hexathelidae and to 11 genera. They occur along the eastern coast of Australia in moist cool habitats.

Most Funnel-web spiders are ground or log dwellers. They live in silk lined burrows and crevices. Their hideouts can easily be identified by the characteristic trip lines radiating from the entrance of the burrow.

These spiders are large (24-32 mm body length) and considered aggressive, biting with little provocation. 6 species, in two genera (Atrax and Hadronyche) are known to cause severe envenomation, in 25% cases of bites, or a total of 64 cases in some 23 years.

Although Australian Funnel-web Spiders often bite without injecting venom, a bite from a large black spider, especially in the Sydney area, should be taken very seriously.

2.1 Atrax

- Sydney Funnel Web Spider (Atrax robustus)

This spider is mostly found within a radius of 160km from Sydney (hence its name), but can generally occur in New South Wales, from Newcastle to Nowra and West to Lithgow .

It is large (up to 45 mm in body length), black or dark brown, and has powerful fangs.

Adult male spiders leave the burrow permanently to seek a mate. Such wandering male spiders may enter houses, especially in summer and fall, and sometimes even find their way into clothing, and thus account for many bites. The male is the most dangerous (unlike most spider species).

It is one of the most venomous and dangerous species of spiders worldwide, and possibly the most dangerous of the Funnel-web Spiders.
The Sydney Funnel-web Spider bite with little provocation, arching back then lunging forward in a downward motion, penetrating its victim's flesh and releasing toxin. The onset of symptoms can occur within minutes.

Symptoms include pain, mouth numbness, salivation, nausea, vomiting, tingling feeling, abdominal pain, profuse sweating, drop in blood pressure, muscular twitching. Respiratory complications, pulmonary edema and cardiac arrest could lead to deaths.

The venom of the Sydney Funnel-web Spider (notably one of its toxins, Robustoxin, a unique presynaptic neurotoxin) in man, other primates) is lethal to man and other primates, but it doesn't affect other mammals, for example cats, dogs or mice, anywhere near as much. However, 83% of the people bitten never develop symptoms that would require the use of antivenin.

2.2 Hadronyche

These spiders occur along the coastal areas and highland forest regions of Australia, from Tasmania to Queensland.

The Atrax robustus antivenin apparently works in all Hadronyche species.

- Southern Tree Funnel-web Spider (Hadronyche cerberea)

Found in New South Wales. Unlike most species of Funnel-web Spiders, this species is a tree dweller. Severe envenomation occurs in 75% of bite cases.

- Northern Tree Funnel-web Spider (Hadronyche formidabilis)

This species is found in Queensland, New South Wales. Its burrow may be in the hollow of a tree trunk or limb, many meters above ground level. Venoms from this species is thought to be approximately equally toxic (both male and female) as male Atrax robustus. They have caused similar cases of envenomation in man (no definite fatalities), and therefore probably contain a robustoxin-like component. Severe envenomation occurs in 63% of bite cases.

- Toowoomba Funnel-web Spider (Hadronyche infensa)

Found in Queensland, New South Wales. Severe envenomation occurs in 14% of bite cases. This species' venom is reported to be at least as toxic (females and males) as male Atrax robustus venom, and therefore may contain a robustoxin-like component.

- Hadronyche versuta

Found in New South Wales. Severe envenomation occurs in 11% of bite cases. Versutoxin (from male and female Hadronyche versuta venom) is structurally very close to robustoxin and there is a strong antigenic cross-reaction between robustoxin and versutoxin.

Other species of Hadronyche spiders are:

- Hadronyche adelaidensis: found in South Australia
- Hadronyche anzses: found in Queensland
- Hadronyche eyrei: found in South Australia
- Hadronyche flindersi: found in South Australia
- Hadronyche hirsuta: found in New Guinea
- Hadronyche insularis: found in the Solomon Islands
- Hadronyche modesta: found in Victoria
- Hadronyche pulvinator: found in Tasmania
- Hadronyche valida: found in Queensland, New South Wales
- Hadronyche venenata: found in Tasmania

3. Mouse spiders (Missulena)

These mygalomorph or primitive spiders belong the family Actinopodidae. Eleven species have been described.(10)

These medium to large spiders measure 15 to 3.8 cm (1/2 to 1 and 1/2 inches) in body length. The male often has a bright red head and elongated fangs. The spiders are quite similar in appearance to other mygalomorph spiders, notably the funnel-webs, but distinguish themselves by their very broad heads.

The name "Mouse Spider" comes from the mistaken belief that this spider excavates a deep mouse-like burrow. In reality, like the trap-door spiders, the Mouse Spider does lives in burrows in the ground, (in banks of rivers, creeks and other waterways, or even in suburban gardens), but the burrows don't go deeper than 30cm. Burrows have a double or single trapdoor and an oval-shaped entrance.

Females remain in or near their burrows ( where they catch insects) throughout their life, and are rarely aggressive. Males wander in search of females in early winter, during the day time, and especially after the rain.

Although not particularly aggressive, the male Mouse Spider will assume a threatening posture if it feels threatened, and even bite if provoked. Its large hard fangs can cause a deep painful bite and a severe illness, and these spiders should be considered dangerous to humans, especially young children.

However, studies have shown that hardly 2.5% of bites result in serious envenomation. But since these spiders' toxins are very close to that of the Funnel-webs, and because they can easily be mistaken for one another, first aid and medical attention should be sought as soon as possible in the case of a bite.

- Eastern Mouse Spider (Missulena bradleyi)

Found in eastern Australia from Queensland to Victoria, and especially in New South Wales.
The toxin d-missulenatoxin-Mb1a was isolated from the venom of Missulena bradleyi, and was shown to be 88% homologous to the Sydney funnel-web spider's robustoxin.

- Redheaded Mouse Spider (Missulena occatoria)

Found across most of the mainland, except southern Victoria and northern Australia. The male of this species has a bright red cephalothorax. Unlike most Missulena females, the female of this species produces copious amounts of highly toxic venom, which is potentially as dangerous as that of the Sydney Funnel-web Spider.

Other species of Mouse Spiders are:

- Missulena dipsaca: found throughout Australia
- Missulena granulosa: found in Western Australia
- Missulena hoggi: found in Western Australia
- Missulena insignis: found throughout Australia
- Northern Mouse Spider (Missulena pruinosa): found in the Northern Territory, around Darwin, and in Western Australia.
- Missulena reflexa: found in South Australia
- Missulena rutraspina: found in Western Australia, South Australia, Victoria
- Missulena torbayensis: found in Western Australia

One species, Missulena tussulena, has been described outside Australia, in Chile.

4. White-Tailed Spider (Lampona)

White-tailed spiders are common in eastern and southern Australia, and have been introduced in New-Zealand.

These spiders belong to the family Lamponidae, a family containing around 60 species.

The whole body of these spiders is cylindrical (cylindrata) and colored mouse gray ("murinus" in latin), or reddish, with a distinctive white spot on their tail (hence their name), and orange-brown legs. Males measure up to 12 mm (1/2 inch) in body length and females up to 18 mm (3/4 inch).

The White-tailed Spider is nocturnal: during the day, it hides in a sac-like web; at night, it hunts (especially for other spiders) in and around houses under bark and logs, and likes to occupy clothing, shoes, and miscellaneous household textiles. Thus, many bites occur while victims are sleeping (30%) or during dressing (40%).

Bites by these spiders are quite common and have been accused of causing severe ulceration and tissue necrosis. But recent studies show that there is no evidence to support this.

The bite can cause an initial burning pain, in some cases severe, and in 44% of cases a persistent red mark, with associated itchiness and pain or lump for 5 to 12 days.

- Lampona cylindrata: found across southern Australia (south east Queensland, New South Wales, Victoria, South Australia, Tasmania, Western Australia) and New Zealand.

- Lampona murina: found in eastern Australia from north-east Queensland to Victoria (Queensland, New South Wales, Victoria) and New Zealand.

Sources:

http://www.entomon.net/venomous-most-deadly-spiders-kevlar-webs.htm
Venomous and Most Deadly Spiders

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Spider pictures

http://venomous-spiders.nanders.dk/
Venomous spiders - poisonous spiders

http://spiders.ucr.edu/dermatol.html
Bites and Stings of medically important venomous arthropods
Richard S. Vetter and P. Kirk Visscher
Department of Entomology, University of California
Published in the International Journal of Dermatology, volume 37, page 481-496, July 1998,

http://en.wikipedia.org/wiki/Latrodectus
Latrodectus

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Spiders of North-West Europe

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http://my.funtrivia.com/submitquiz.cfm?quiz=261121

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