Katipo

The katipo (Latrodectus katipo) is an endangered species of spider native to New Zealand. It is a member of the genus Latrodectus, along with the Australian redback spider (L. hasseltii), and the North American black widow spiders. The species is venomous to humans, capable of delivering a comparatively dangerous spider bite. Katipo is a Māori name and means "night-stinger". It is a small to medium-sized spider with the female having a round black or brown pea-sized body. Red katipo females, found in the South Island and the lower half of the North Island, are always black, and have a distinctive red stripe bordered in white on their bodies. In black katipo females, found in the upper half of the North Island, this stripe is absent, pale, yellow, or replaced with cream-coloured blotches. The two forms were previously thought to be separate species, but 2008 research determined they were the same species with different colouration. The male is much smaller than the female and quite different in appearance, 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 southernmost regions. Spinning an irregular tangled web amongst dune plants or other debris, they feed mainly on ground dwelling insects.

After mating in August or September, 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 the loss of habitat and colonisation of their natural habitat by other exotic spiders, the katipo is being faced with extinction.

A bite from the katipo produces 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 19th century. An antivenom is available in New Zealand for treatment. 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,^[2] despite sightings being very rare.^[3]

Taxonomy

Although the 'kātĕpo' was reported to the Linnean Society as early as 1855,^[4] the katipo was formally described as Latrodectus katipo by L. Powell in 1870.^[5] Spiders of the genus Latrodectus have a worldwide distribution and include all of the commonly known widow spiders, namely the North American black widow spider (Latrodectus mactans), the brown widow (Latrodectus geometricus) and the European black widow (Latrodectus tredecimguttatus). The katipo's closest relative is the Australian redback spider (Latrodectus hasseltii)^[6][7] Latrodectus katipo and L. atritus (black katipo) were previously thought to be two separate species,^[8][9] however, research has shown that there is only one species, L. katipo, and colour variation in that species is clinal over latitude and correlates significantly with mean annual temperature.^[7] The 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 hasseltii katipo. Further research has shown that the katipo is distinct from the redback, having slight structural differences and striking differences in habitat preference, and it remains its own species.^[7][8][9] The katipo's family Theridiidae 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.^[10]

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).^[11] This name was apparently given to the spider due to the Māori belief that the spiders bite at night.^[12] Other common names include red katipo, black katipo and New Zealand's redback.^[13]

Description

The katipo is a small to medium-sized spider.^[14] The mature female has a body size of about 8 millimetres (0.31 in) with a leg span of up to 32 millimetres (1.3 in). The red katipo female, found in the South Island and the lower North Island, 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.^{[2][9][15][16][17][18][19]} The black katipo female, found in the upper North Island, does not have a red stripe on the top of her body, and the abdominal colouration is usually lighter, but is otherwise very similar in appearance to the red katipo. The hourglass pattern on the underside of the abdomen may also be less distinct, losing the middle section, and may even be absent.^[2] Variations also exist whose abdomen, cephalothorax, or entire body is brown, sometimes with a dull red or yellow stripe, or cream-coloured spots on its upper side.^[2]

Adult males and juveniles are quite different in appearance 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 coloration into adulthood.^{[9][17][20][21]} Due to its much smaller size, Urquhart (1886) believed the male to be a separate species and named it Theridion melanozantha.^[22] This was not rectified until 1933 when it was correctly identified as the male Latrodectus katipo.^[23]

Habitat

The katipo is restricted to a highly specialised habitat and is only found near the seashore living among 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 sometimes be associated with dunes several kilometres from the sea when these dunes extend inland for long distances.^[10]

Webs are typically established in low-growing dune plants and other vegetation such as the native Pingao (Desmoschoenus spiralis) or the introduced marram grass (Ammophila arenaria).^[13] They may also build their webs under driftwood, stones, or other debris such as empty tin cans or bottles.^[14][21] Webs are almost always constructed over open sand and near the ground so as to catch crawling insects for food.^[15] Spiders inhabiting dune grasses construct their webs in open spaces between the grass tufts, while spiders inhabiting areas of shrubbery do so on the underside of a plant overhanging open sand.^[17] It has been found that these patches of open sand are necessary 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.^[17] 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.^[13][15]

Like other theridiid spiders, the web is a disorganised, irregular tangle of fine textured silk. It is hammock-shaped and is made up of opaque yellowish-white silk.^[16] 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,^[15] although the katipo can normally be found near the main body of the web.^[13] The plants it builds its web in provide support and shelter for the nest.^[15]

Range

The katipo is endemic to New Zealand.^[13] In the North Island it is found along the West Coast from Wellington to North Cape. 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.^[10][20] This southern limit is due to the katipo needing temperatures higher than about 17 °C (63 °F) to be maintained during the development of their eggs - in the southern areas of New Zealand it is typically colder than this.^[15]

The red katipo is found south of approximately 39°15′ S (the western tip of Taranaki on the west coast, and just north of Waipatiki Beach in Hawke's Bay on the east coast). The black katipo is found north of approximately 38° S (Aotea Harbour, just north of Kāwhia on the west coast, and Waipiro Bay and just south of the Bay of Plenty on the east coast). Both forms are found in the area in-between these latitudes.^[7]

Behavior

Diet

The katipo typically catches wandering ground invertebrates such as beetles (e.g. Cecyropa modesta) or amphipods (e.g. Bellorchestia quoyana), but it may occasionally catch moths, flies, and other spiders.^[13][15][24] Katipo can catch insects much larger than themselves. These larger insects often become entangled in the web and in the ensuing struggle, the web's 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, turns so that the spinnerets are facing the insect and spins silk over it. Like most theridiids, the tarsi of the hind legs have a row of strong curved bristles which are arranged as a comb. The katipo uses these to scoop sticky silk from her spinnerets and throws it over the insect with a series of rapid movements.^[9] After the insect is firmly immobilised, she bites it several times, usually at the joints, before spinning more silk to strengthen the web, and 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 male's hunting behaviour is similar to the female's, although may not be as vigorous due to its smaller size.^[15]

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 female's web and vibrate the silk as he approaches her. The female is usually aggressive 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, when 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.^[15] 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.^[15]

The females lay their eggs in November or December.^[13] The eggs are round, about the size of a mustard seed, and are a transparent, purply red. They are held together in a cream-coloured, round, ball shaped egg sac which is about 12 millimetres (0.47 in) 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.^[13][15] Over time the exterior of the egg sac may become covered with sand.^[11] After six weeks of incubation, during January and February, the spiderlings hatch.^[13] The young spiders then disperse from the web. At present, little is known about the dispersal mechanism that 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.^[13]

The close relationship between the katipo and redback is shown when mating, The male redback is able to successfully 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 approaches the web it triggers a predatory response in the female leading to the katipo being eaten before mating occurs.^[13] There is evidence of interbreeding between katipo and redbacks in the wild.^[7]

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.^[10]

Population decline

The katipo is an endangered species and has recently become threatened with extinction.^[13] 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.^[25] A number of reasons have contributed to its decline; the major factors appear to be loss of habitat and declining quality of the remaining habitat.^[10] Human interference with their natural habitat has been occurring for over a century following European settlement. Coastal dune modification resulting from agriculture, forestry, or urban development along with recreational activities like the use of beach buggies, off road vehicles, beach horse riding and driftwood collection have destroyed or changed areas where katipo lives.^[10][17][26] The introduction of many invasive exotic plants has also contributed to the decline of suitable habitat.^[17]

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.^[3][13] 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.^[10] S. capensis also belongs to the family Theridiidae and shares many of the katipo's features. It is of similar size, shape, general coloration, it lacks the red stripe on its back, but may have some red, orange or yellow on its abdomen,^[17] 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’.^[2]

In June 2010 the katipo was given full protection under the Wildlife Act to assist conservation efforts. Previously, it had no protection under the Act.^[27]

Toxicology

The katipo has medically significant venom in humans, although bites are rare.^[21] The incidence of bites is low as it is a shy, non-aggressive spider. Their narrow range, diminishing population, and human awareness of where they live means interaction between humans and the spider is minimal.^[19] The katipo will only bite as a last resort; if molested, the spider will usually fold up into a ball and drop to the ground or retreat 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 if 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 sometimes move offensively to bite any threat.^[12]

Bites from Katipo spiders produce a syndrome known as latrodectism.^[19] The venoms of all Latrodectus spiders are thought to contain similar components with the neurotoxin α-latrotoxin the main agent responsible.^[28][29] Most bites are caused by female spiders; the male katipo was considered too small to cause systemic envenoming in humans.^[12] However, bites from male redback spiders have been reported suggesting male Latrodectus spiders can cause envenoming in humans. Although bites by male spiders are much rarer than those 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.^[30] Māori legends recall many deaths, the last of which appears to have been a Māori girl who - according to the missionary Thomas Chapman - died in approximately 1849.^[31] While there were reports of severe katipo bites in 19th or early 20th century records,^[12] no other fatalities from spider bites have since been reported in New Zealand.^[32] The most recently reported katipo bite as of 2012 was to a Canadian tourist in 2010.^[33] A fatality was reported in the Evening Post, Volume LXII, Issue 75, 25 September 1901, Page 5. "AUCKLAND, This Day. Mr. George Twidle, aged 47, son of Mr. George Twidle of Pukekohe, was bitten by a katipo spider on. September 16. His arm swelled, and he suffered great pain till Saturday last, when he died. He leaves a widow and several children." ^[34]

Symptoms

The clinical features of latrodectism are similar for all species of Latrodectus spiders and is generally characterised by extreme pain.^[12][30] 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.^[30][35] Rare complications include seizure, coma, pulmonary edema, respiratory failure or localised skin infection.^[36] 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.^[37][38]

Treatment

Treatment is based on the severity of the bite; the majority of cases do not require medical care and patients with localised pain, swelling and redness usually only require local application of ice and routine analgesics. Hospital assessment is recommended if simple analgesia does not resolve local pain or clinical features of systemic envenoming occur.^[39][40] In more severe bites, Redback antivenom can be given.^[19] Redback antivenom can also cross-neutralise katipo venom,^[41] and it is used to treat envenoming from Latrodectus katipo in New Zealand.^[19][29] It is available from most major New Zealand hospitals.^[14] Antivenom will usually relieve 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.^[29] Particular indications for using antivenom are local then generalised pain, sweating or hypertension.^[42] However, good evidence to support the effectiveness of widow spider antivenoms is lacking and studies have cast some doubt on antivenoms efficacy in latrodectism.^[30][43] Pain relief agents, such as parenteral opiates, or benzodiazepines may be required as adjunct agents.^[19][38]

References

External links

• Data related to Latrodectus katipo at Wikispecies
• Media related to Latrodectus katipo at Wikimedia Commons
• Photos of male katipo, and different forms of female black katipo by Bryce McQuillan on flickr
• Katipo spider on the website of the Museum of New Zealand Te Papa Tongarewa