''Dolomedes schauinslandi'' or the Rangatira spider is a large

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

of the family

Pisauridae Nursery web spiders (Pisauridae) is a family of Araneomorphae, araneomorph spiders first described by Eugène Simon in 1890. They resemble wolf spiders (Lycosidae) except for several key differences. Wolf spiders have two very prominent eyes in ad ...

. It is only found on South East Island (Rangatira), Houruakopara and

Mangere Island Mangere Island (Moriori: ''Maung’ Rē'') is part of the Chatham Islands archipelago, located about east of New Zealand's South Island and has an area of . The island lies off the west coast of Pitt Island, south-east of the main settlement in ...

s in the

Chatham Islands The Chatham Islands ( ) (Moriori: ''Rēkohu'', 'Misty Sun'; mi, Wharekauri) are an archipelago in the Pacific Ocean about east of New Zealand's South Island. They are administered as part of New Zealand. The archipelago consists of about te ...

, New Zealand. It is one of New Zealand's largest and rarest spiders.

Description

This large ''

Dolomedes ''Dolomedes'' is a genus of large spiders of the family Pisauridae. They are also known as fishing spiders, raft spiders, dock spiders or wharf spiders. Almost all ''Dolomedes'' species are semiaquatic, with the exception of the tree-dwelling ...

'' spider was first described by

Eugène Simon Eugène Louis Simon (; 30 April 1848 – 17 November 1924) was a French naturalist who worked particularly on insects and spiders, but also on birds and plants. He is by far the most prolific spider taxonomist in history, describing over 4, ...

in 1899 as "one of the biggest and most robust species of the genus ''Dolomedes''". This species demonstrates

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

, with male body lengths of and females of . Both males and females are substantially larger than other New Zealand ''Dolomedes'' species. The

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

and legs are red-brown with orange stripes on the centre and sides of the abdomen. They have bright eye shine and can be spotted at night from 20 metres away.

Ecology

''D. schauinslandi'' is active at night in forest and scrubland habitat, where it hunts for

wētā Wētā (also spelt weta) is the common name for a group of about 100 insect species in the families Anostostomatidae and Rhaphidophoridae endemic to New Zealand. They are giant flightless crickets, and some are among the heaviest insects in th ...

on the

forest floor The forest floor, also called detritus, duff and the O horizon, is one of the most distinctive features of a forest ecosystem. It mainly consists of shed vegetative parts, such as leaves, branches, bark, and stems, existing in various stage ...

or tree trunks. Its predators may include mice and

weka The weka, also known as the Māori hen or woodhen (''Gallirallus australis'') is a flightless bird species of the rail family. It is endemic to New Zealand. It is the only extant member of the genus ''Gallirallus''. Four subspecies are recognize ...

, which would explain its absence from

Pitt Island Pitt Island is the second largest island in the Chatham Islands, Chatham Archipelago, New Zealand. It is called ''Rangiauria'' in Māori language, Māori and ''Rangiaotea'' in ''Moriori language, Moriori.Government of New Zealand, Dept. of Cons ...

, where it was described as common in the original species description. Mating has not been observed, but females have been observed carrying egg sacs in their

chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated fangs, or similarly ...

in November and December and guarding their nursery from December to February, as would be expected for a

nursery web spider Nursery web spiders (Pisauridae) is a family of araneomorph spiders first described by Eugène Simon in 1890. They resemble wolf spiders (Lycosidae) except for several key differences. Wolf spiders have two very prominent eyes in addition to the o ...

Conservation

This species, the only ''Dolomedes'' known from the Chatham Islands, is classified as having a relict population status, due to it surviving in less than 10% of its previously known habitat. It was probably present on the main Chatham Island prior to human settlement, as it is found on mouse-free Houruakopara Island which is only 200 m offshore. The other two islands in its current range, Mangere and Rangatira, are now free of introduced mammals and have restricted access to maintain their predator-free status; Rangatira was farmed up to the 1960s, but cats, mice, and rats were never introduced there. The Rangatira spider was first described from specimens collected on Pitt Island, but despite substantial surveys it has not been seen there since the early 1900s. Mice, which are known spider predators, were accidentally introduced to Pitt some time before 1951, and may have driven ''D.'' ''schauinslandi'' extinct there. It is possible that this species could re-establish itself on Pitt Island, if there was suitable predator-free habitat (Pitt Island has mice but not rats); spiderlings lift their abdomens when exposed to a breeze in the lab, which is a behaviour associated with aerial travel by

ballooning Ballooning may refer to: * Hot air ballooning * Balloon (aeronautics) * Ballooning (spider) * Ballooning degeneration, a disease * Memory ballooning See also * Balloon (disambiguation) A balloon is a flexible container for (partially or fully) co ...

References

External links

* Rangatira spider discussed on RNZ ''Critter of the Week''
18 May 2018
{{Taxonbar, from=Q2042814 schauinslandi Spiders of New Zealand Endemic fauna of New Zealand Spiders described in 1899 Endemic spiders of New Zealand