Katipo

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Katipo spider
Female Katipo spider
Conservation status
Endangered
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Arachnida Order: Araneae Family: Theridiidae Genus: Latrodectus Species: L. katipo
Binomial name
Latrodectus katipo Powell, 1870

The katipo or red katipo (Latrodectus katipo) is a endangered, venomous spider native to New Zealand. It is a widow spider and is related to the black katipo, the Australian redback spider, and the North American black widow spiders. Katipo is a Māori name and means "night-stinger". It is a small to medium-sized spider with the female having a distinctive black body with a white bordered red stripe on its back. The male is much smaller than the female and quite different in apperance being white with black stripes and red diamond shaped markings. Katipo have a narrow habitat being only found living in sand dunes close to the seashore. They range throughout most of coastal New Zealand but are not found at the northern or southern most portions of the country. Spinning a irregular tangled web amongst dune plants or other debris they feed mainly on ground dwelling insects.

The spider mates in August or September and the female produces five or six egg sacs in November or December. The spiderlings hatch during January and February and disperse into surrounding plants. Due to loss of habitat and colonisation of their natural habitat by other exotic spiders the katipo is being faced with extintion.

A bite from the katipo is poisonous to humans producing a toxic syndrome known as latrodectism. Symptoms include extreme pain and potentially systemic effects such as hypertension, seizure, or coma. Bites are rare and deaths have not been reported since the 18th century. An antivenom is available in New Zealand for the treatment of envenoming. The katipo is particularly notable in New Zealand as the nation is almost entirely devoid of dangerous native wildlife. This unique status has led to the spider becoming well-known,^[1] despite sightings being very rare.^[2]

Contents 1 Taxonomy 2 Description 3 Habitat 4 Range 5 Behavior 5.1 Diet 5.2 Reproduction 6 Predators 7 Population decline 8 Toxicology 8.1 Symptoms 8.2 Treatment 9 Footnotes

[edit] Taxonomy

The katipo was formally described as Latrodectus katipo by L Powell in 1870.^[3] Latrodectus spiders have a worldwide distribution and belong to the family Theridiidae. This family of spiders has a large number of species both in New Zealand and worldwide and are commonly known as tangle-web spiders, cobweb spiders or comb-footed spiders.^[4] The genus Latrodectus contains all the commonly known widow spiders including the North American black widow spider (Latrodectus mactans), the brown widow (Latrodectus geometricus) and the European black widow (Latrodectus tredecimguttatus). The katipo's closest relatives are the New Zealand native black katipo (Latrodectus atritus) and the Australian redback spider (Latrodectus hasselti). The katipo and black katipo are so closely related to the redback that they were at one stage thought to be a subspecies. It was proposed that the katipo be named Latrodectus hasselti hasselti and the black katipo Latrodectus hasselti atritus. Further research has shown that the katipo is distinct from the redback and it remains its own species.^[5]

The common name, katipo, is a Māori name and means night stinger; it is derived from two words, kakati (to sting), and po (the night).^[6] This name was apparently given to the spider due to the Māori belief that the spiders bite at night.^[7] Other common names include red katipo and New Zealand’s redback.^[8]

[edit] Description

The katipo is a small to medium-sized spider.^[9] The mature female has a body size of about 8 mm with a leg span of up to 32 mm. It has a large black globular abdomen, about the size of a garden pea, with slender legs and a white-bordered orange or red stripe on its back that runs from the uppermost surface of the abdomen back to the spinnerets. The dark velvet-black abdomen is described as satin or silky in appearance, rather than being shiny. The underside of the abdomen is black and has a red patch or partial red hourglass-shaped marking. It has mainly black legs with the extremities changing to brown.^{[1][10][11][12][13][14]}

Adult males and juveniles are quite different in apperance to the female. They are smaller in size, being about one sixth the size of an adult female. Juveniles have a brown carapace, with a predominantly white abdomen which has a series of red-orange diamonds running along the dorsal region bordered on either side by irregular black lines. Males retain this colouration into adulthood.^{[10][13][15][16]} Due to its much smaller size Urquhart (1886) believed the male of the katipo to be a separate species and named it Theridion melanozantha.^[17] This was not rectified until 1933 when it was correctly identified as the male Latrodectus katipo.^[5]

[edit] Habitat

The katipo has a highly specialised habitat and is strictly found near the seashore living amongst sand dunes. They generally reside on the landward side of dunes closest to the coast where they are most sheltered from storms and sand movement. They can, in some situations, be associated with dunes several kilometres from the sea when these dunes extend inland for long distances.^[4]

Webs are typically established in low-growing dune plants and other vegetation such as New Zealand’s native pingao (Desmoschoenus spiralis) or the introduced marram grass (Ammophila arenaria).^[8] They may also build their webs under driftwood, stones, or other debris such as empty tin cans or bottles.^[9][16] Webs are almost always constructed over open sand and near the ground so as to catch crawling insects for its food.^[11] Spiders inhabiting dune grasses construct their webs in open spaces between the grass tufts, or when the spider inhabaits areas of shrubery, the web is on the underside of the plant overhanging open sand.^[13] It has been found that these patches of open sand are required for katipo to build their webs as plants that envelop sand dunes in dense cover, such as exotic plants like kikuyu or buffalo grass, create an environment unsuitable for web construction.^[13] The katipo therefore prefers to spin its web amongst pingao plants as this plants growth pattern leaves patches of sand between each plant. The wind can then blow insects and other prey through these gaps and into the web. Marram grass has been extensively planted in New Zealand to help stabilise sand dunes and has largely replaced pingao in many areas. Because marram grass grows in a very tight formation only leaving small gaps between tuffs, this makes it difficult for the katipo to construct a suitable web for capturing prey.^[11][8]

Similarly to other theridiid spiders, the actual web is a disorganised, irregular tangle of fine textured silk. It is hammock shaped and is made up of opaque yellowish-white silk.^[12] The web consists of a broad base with many supporting threads above and below, including a number of sticky guy lines anchored to debris in the sand. A cone shaped retreat is built in the lower part of the web,^[11] although the katipo can normally be found near the main body of the web.^[8] The plants within which it builds its web provide support and shelter for the nest.^[11]

[edit] Range

The katipo is native to, and only, found in New Zealand.^[8] In the North Island it is found along the West Coast from Wellington to north of Wanganui, New Plymouth and Waitara. It is rare or extinct in the north of the North Island. On the east coast of the North Island it occurs irregularly, however it is abundant on Great Barrier Island. In the South Island it is found in coastal regions south to Dunedin on the east coast and south to Greymouth on the west coast.^[4][15] This southern limit is due to the katipo needing temperatures higher than about 17 degrees celsius to be maintained during the development of their eggs, explaining why they are not found in the southern areas of New Zealand where it is typically colder than this.^[11]

[edit] Behavior

[edit] Diet

The katipo typically catches wandering ground invertebrates such as beetles (e.g. Cecyropa modesta) or Amphipods (e.g. Talorchestia quoyana), but it may occasionally catch moths, flies, and other spiders.^[8][11][18] Katipo can catch insects much larger than themselves. These larger insects often become entangled in the web and in the ensuing struggle the webs ground anchor line breaks. Due to the silks elasticity this causes the prey to become suspended a few centimetres off the ground. The katipo then moves to the prey and spins silk over it, after the insect is firmly immobilised she bites it several times, usually at the joints, before spinning more silk to strengthen the web then administering a last long bite which ultimately kills the insect. The spider then moves the prey up into the web until it is ready to eat. If food is readily available then it is common to see five or six insects hanging in the web waiting to be ingested. The males hunting behaviour is very similar to the females although due to its smaller size may not be as vigorous.^[11]

[edit] Reproduction

The male wanders as an adult and in August or September goes looking for the females' webs to mate. The male will enter the famles web and vibrate the silk as he approaches her. The female is usually aggresive at first and will chase the male from the web. The Courtship process consists of the male bobbing, plucking and tweaking the web along with periods of cautious approach and being chased by the female. Eventually she becomes docile and allows him to approach, the male will then approach the female as she hangs quietly upside down in the web. The male moves onto her ventral abdomen, tapping her rapidly until she moves to align his abdomen above hers. He then inserts his palps one at a time, leaving the female between each insertion. Copulation occurs over 10 to 30 minutes.^[11] After mating the male retreats to groom, which is performed by running his palps and legs through his fangs and wiping them over his body. The male is not eaten by the female unlike some other widow spiders.^[11]

The females lay their eggs in November or December.^[8] The eggs are round, about the size of a mustard seed, and are transparent purply red. They are held together in a cream coloured, round ball shaped egg sac which is about 12 millimetres in diameter. The female constructs five or six egg sacs over the next three to four weeks. Each egg sac contains about 70 to 90 fertilised eggs. The egg sacs are hung in the centre of the spiders web and the female spins more silk over them.^[8][11] Over time the exterior of the egg sac may become covered with sand.^[6] After six weeks of incubation, during January and February, the spiderlings hatch.^[8] The young spiders then disperse from the web. At present little is known about the dispersal mechanism the spiderlings use to move away from the nest. In one study, observing spiders over 24 hours, 28% used a ballooning method which is where the young spiders use heat currents to carry themselves away from the nest suspended by a single web strand. While the majority, 61%, used a bridging method where the spiderling uses its silk to move to nearby plants, and 11% still remained in the nest. The young spiderlings reach full maturity the following spring.^[8]

The close relationship between the katipo and redback is shown when mating, The male redback is able to succesfully mate with a female katipo producing hybrid offspring. However, the male katipo can not mate with the female redback as the male katipo is heavier than the male redback and when it approachs the web it triggers a predatory response in the female leading to the katipo being eaten before mating occurs.^[8] In areas where their habitats overlap, the black katipo does not interbreed with the katipo. Laboratory studies have confirmed the katipo and black katipo do not generally interbreed and if they do, the resulting eggs are infertile.^[11]

[edit] Predators

The katipo has only one known direct predator. A small, undescribed native wasp from the family Ichneumonidae has been observed feeding on katipo eggs.^[4]

[edit] Population decline

The katipo is an endangered species and recently has become threatened with extinction.^[8] It is estimated that there are only a few thousand katipo left in about 50 areas in the North Island and eight in the South Island.^[19] A number of reasons have contributed to its numbers being in decline; the major factors appear to be loss of habitat and declining quality of the remaining habitat.^[4] Human interference with their natural habitat has been occurring for over a century following European settlemen. Coastal dune modification resulting from agriculture, forestry, or urban development along with recreational activites like the use of beach buggies, off road vehicles, beach horse riding and driftwood collection have destroyed or changed areas in which katipo live.^[4][13][20] The introduction of many aggressive exotic plants also contributes to restricting suitable habitats.^[13]

Additionally foreign spiders have colonised areas where suitable habitat remains. The major coloniser is the South African spider Steatoda capensis. It was first reported in the 1990s and may have displaced the katipo along the west coast of the North Island from Wellington to Wanganui.^[2][8] Although both the katipo and S. capensis have been found sharing the same dune systems or even co-existing under the same piece of driftwood suggesting that the two species can co-exist in similar habitats. It is possible that the displacement of the katipo by S. capensis is due to its ability to recolonise areas from which the katipo had been displaced after storms or other dune modifications. Furthermore S. capensis breeds year-round, produces more offspring and lives in a greater range of habitats which leads to greater pressure on the katipo.^[4] S. capensis shares many of the katipo's features, it is of similar size, shape, general colouration, it lacks the red stripe on its back, but may have some red, orange or yellow on its abdomen,^[13] as well as the general location where katipos are found. Due to these similarities it is commonly known in New Zealand as the ‘false katipo’.^[1]

[edit] Toxicology

Main article: Latrodectism

The katipo has medically significant venom in humans although bites are rare.^[16] The incidence of bites is low as they are a shy, non aggressive spider. Additionally their narrow habit, diminishing population, and human awareness of where they live means interaction between humans and the spider is typically minimal. The katipo will only bite as a last resort; if molested the katipo will usually fold up into a ball and drop to the ground or move to the nearest cover. If the threat continues the spider may throw out silk against the interference. When restrained in any way or held against skin, such as when tangled up in clothing, the spider will then bite defensively. However, if the female is with an egg sac it will remain close by it and sometime move offensively to bite any threat.^[7]

Bites from Katipo spiders produce a syndrome known as latrodectism. Most bites are caused by female spiders; the male katipo was considered too small to cause systemic envenoming in humans.^[7] However, bites from male redback spiders have been reported suggesting male Latrodectus spiders can bite and cause envenoming in humans. Although it has been found that bites by male spiders are much rarer than bites by females, perhaps due to their smaller jaws rather than lacking venom of similar potency to females or being unable to administer an effective bite.^[21] Māori legends recall many deaths and there were reports of severe katipo bites in 19th or early 20th century records, however, the only two reported fatalities were recorded in the 18th century.^[7] No other fatalities from spider bites have ever been reported in New Zealand.^[22]

[edit] Symptoms

The clinical features of latrodectism are similar for all species of Latrodectus spiders and is generally characterised by extreme pain.^[7][21] Initially the bite may be painful but sometimes only feels like a pin prick or mild burning sensation. Within an hour victims generally develop more severe local pain with local sweating and sometimes piloerection (goosebumps). Pain, swelling and redness spread proximally from the site. Less commonly 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.^[21][23] Rare complications include seizure, coma, pulmonary edema, respiratory failure or localised skin infection.^[24] The duration of effects can range from a few hours to days, with severe pain persisting for over 24 hours after being bitten in some cases.^[25][26]

[edit] Treatment

Treatment consists of observation in a medical facility for six hours from time of the bite.^[23] 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. Redback antivenom has shown cross neutralisation with katipo venom^[27] and it is used to treat envenoming from Latrodectus katipo in New Zealand.^[28] It is available from most major New Zealand hospitals.^[9] Antivenom will usually give relief to symptoms of systemic envenoming and is indicated in anyone suffering symptoms consistent with Latrodectus envenoming. Unlike some other antivenoms it is not limited to patients with signs of severe, systemic envenoming.^[28] Particular indications for using antivenom are local then generalised pain, sweating or hypertension.^[29] However, good evidence to support the effectiveness of widow spider antivenoms is lacking and studies have cast some doubt on antivenoms efficacy in latrodectism.^[21] Pain relief agents such as parenteral opiates may be required as adjunct agents.^[26]

[edit] Footnotes