Great raft spider

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Great raft spider
D.plantarius on water surface.jpg
An adult female great raft spider on the surface of a water pool
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Pisauridae
Genus: Dolomedes
Species:
D. plantarius
Binomial name
Dolomedes plantarius
Recorded range of Dolomedes plantarius.png
Countries with a recorded population of D. plantarius
Synonyms

Araneus plantarius
Aranea viridata
Dolomedes riparius

Contents

The great raft spider or fen raft spider (Dolomedes plantarius) is a European species of spider in the family Pisauridae. Like other Dolomedes spiders, it is semiaquatic, hunting its prey on the surface of water. It occurs mainly in neutral to alkaline, unpolluted water of fens and grazing marsh.

Taxonomy

The species was first described by arachnologist Carl Alexander Clerck in 1757 as Araneus plantarius. Its genus was reclassified by Pierre André Latreille in 1804 to Dolomedes . [3] The species has also been described under the name Aranea viridata by Müller and as Dolomedes riparius by Hahn. [4] The species is currently recognised as Dolomedes plantarius and has two widely recognised common names: the great raft spider and the fen raft spider. [5]

Morphology

D. plantarius is a large species within its range. Adult females can have bodies of slightly over 20mm in length with a span of 70mm including their legs. It is typically black or brown in colouration with white or cream stripes along the sides of the body. [6] It is very similar in appearance to the closely related raft spider Dolomedes fimbriatus with which it is often misidentified.

Ecology and behaviour

Habitat

The great raft spider, as with most other Dolomedes species, is a semi-aquatic spider. It inhabits lowland fen and grazing marsh areas and is dependent on the presence of standing or slow moving neutral to alkaline water. Within these areas it can be found on the margins of pools or ditches. Emergent vegetation is highly important for use as perches for hunting and basking and to support nursery webs. As a warmth loving species they avoid areas where water surfaces are shaded. [5]

Diet and feeding

Great raft spiders are predatory and hunt from perches at the water's edge. They primarily feed on aquatic invertebrates such as pond skaters, dragonfly larvae and smaller aquatic spiders, as well as small fish. They will also feed on drowning terrestrial invertebrates and have been known to catch small vertebrates such as sticklebacks and tadpoles. [6] To hunt aquatic prey they have developed a sensory system of chaetae, a covering of sensory hairs on its legs. These are used to detect the vibrations made as prey hits the surface or moves through the water. It will typically position itself with the back legs on a plant stem and the front legs on the water surface to be able to detect any prey. When prey is found the spider is able to run across the surface of the water to reach it by use of surface tension. They are also known to hunt underwater by running down the stems of plants to reach prey, this can also be used to avoid capture by predators. [6]

Life cycle and reproduction

A female great raft spider with egg sac D.plantarius female with eggs.jpg
A female great raft spider with egg sac

Water is essential to the whole life cycle of the great raft spider. The spiders will live for two and a half years. As juveniles they will hibernate over the winter and will mature into adults during their final spring. In the UK, adults will usually have two breeding attempts between July and September.

The chaetae sensory system is used to help find a mate and courtship is carried out on the water. The male will slowly and carefully approach the female while tapping the water surface with its legs. When they are close they perform a slow bobbing of the body. If accepted the mating is brief and over in seconds. [6]

The female will lay several hundred eggs in a silk sac, about 10mm across, which they carry under their bodies for around three weeks. During this time she will periodically dip the sac into water to prevent the eggs from drying out. She will also locate a suitable nest site amongst the emergent vegetation, this will usually be between 10 and 100 cm above the water. Shortly prior to hatching she will construct a tent-like nursery web within which she can guard the young until they disperse into the surroundings, usually five to nine days after hatching.

If a second brood is attempted later in the summer these are usually smaller and less likely to be successful. Courtship and mating usually takes place early in the season and adult males will die shortly after with most dead by late July. Females will survive until the end of the summer. [7]

Distribution

A male great raft spider in Latvia Dolomedes plantarius spider.jpg
A male great raft spider in Latvia

Populations of the great raft spider are found throughout Europe and Russia, [2] in Austria, Belarus, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Georgia (country), Germany, Hungary, Italy, Latvia, Lithuania, Norway, the Netherlands, Poland, Romania, Serbia, Slovakia, Sweden, Switzerland and the United Kingdom. [1] [8] [9]

In 1956 an outlying population was discovered for the first time in the United Kingdom at Redgrave and Lopham Fen by arachnologist Eric Duffey. A further two populations have since been identified at the Pevensey Levels in East Sussex by Peter Kirby in 1988 and near Swansea, South Wales, by Mike Clark in 2003. [10] [11] The species was also recorded in the 1960s at Sound Heath in Cheshire. [12] The lack of historical record makes it very difficult to estimate the extent of its decline or explain the widely separated current distribution in the UK.

Conservation

Cladium reed beds at Redgrave and Lopham Fen typical of D. plantarius habitat Redgrave and South Lopham Fen.jpg
Cladium reed beds at Redgrave and Lopham Fen typical of D. plantarius habitat

Although the species is widely distributed in Europe, under-recording and confusion over identification make assessment of its status difficult. Populations are known to have declined substantially throughout its range particularly in western and central areas but remaining populations are believed to be well established in Scandinavia and the Baltic States. [13] These reductions in population are primarily due to the degradation and loss of habitat. The great raft spider is listed as a vulnerable species on the IUCN Red List. [1]

United Kingdom

The great raft spider has only been identified at twelve sites in the UK. [14] Due to this extreme rarity it is listed as vulnerable, and was listed as endangered prior to discovery of the third site and reassessment of its status following changes to assessment criteria. It is classified as Nationally Rare. It is protected under Schedule 5 of the Wildlife and Countryside Act 1981 in England and Wales, and the Nature Conservation (Scotland) Act 2004 in Scotland, and was provided a Species Action Plan in 1999. [13] Revised targets were published in 2006 with reports on targets published in 2002, 2005 and 2008. [15] When the UK Biodiversity Action Plan was succeeded by the UK Post-2010 Biodiversity Framework, the great raft spider was listed as a 'species of principal importance' under Section 41 of the Natural Environment and Rural Communities Act 2006. Principal threats to the species in the UK are identified as water abstraction, inappropriate ditch management, deterioration in water quality and the loss of suitable wetland habitat.

Original targets aimed to: Increase the range of the population by ten-fold and to increase the population density to a mean maximum of around 15 individuals per pool at Redgrave and Lopham Fen. To maintain the density and range of the fen raft spider on the Pevensey Levels and to introduce populations to two suitable new sites by 2010. [13] In 2006, these were revised to: Increase the range of the spider to 13 Ha of habitat occupied 3 years in 5 by 2010 and to 65 Ha by 2020 at Redgrave & Lopham Fen. To prevent an overall decrease in range at Pevensey Levels at any time from levels recorded in 1990 and to increase sites with sustainable populations by 6 by 2010 and 12 by 2020. [15]

The spider was first identified in the UK in 1956, at Redgrave and Lopham Fen. Following their discovery, a number of new pools were dug to encourage population expansion. However, water extraction from the nearby borehole and a series of droughts in the 1980s reduced the population to only two isolated areas on the reserve. Throughout this period irrigation of the pools inhabited by the spider enabled the continuation of the population. The removal of the borehole in 1999 was expected to trigger an increase in population as water levels returned to normal. However, a study carried out in 2006 showed that no noticeable change had occurred. The population of the fen raft spider at the site remains small and restricted in distribution, but stable. Recommendations for future management of the population include increasing the depths of turf pool, creating more pool habitats and greater, more focused use of water management in the reserve. [16]

A second population, which had previously been believed to be the similar Dolomedes fimbriatus , was identified in 1988 at the Pevensey Levels in East Sussex. A 1992 survey estimated the population at over 3000 adult females in summer. This population is considered stable and conservation efforts at the site have focused on maintaining this level. [15] A population has been found at a small artificial pond site which derived from Pevensey material. A review of the Pevensey population since its last count has been recommended. [17]

The spider was first found in South Wales in 2003 in the disused Tennant Canal at Pant-y-Sais Fen. [18] Surveying found a stable population as well as identifying further occurrences at the nearby Crymlyn Bog and in connecting wetlands [11] but the full range of the spider is not fully known. This due to the difficulty of surveying work in wetland terrain and problems with identification. The habitat at the site is considered good enough for the population not to be declining. [19]

Reintroduction

In October 2010 the first introduction of a great raft spider population into a new site in the UK was carried out in a joint project by Natural England and Suffolk Wildlife Trust and supported by a grant from the BBC Wildlife Fund. [20] The project saw around 3000 spiderlings bred and reared by Dr. Helen Smith and the John Innes Centre, 1600 of which were released into suitable dykes at the Suffolk Wildlife Trust Castle Marshes nature reserve. The site is part of the Suffolk Broads and lies 50 kilometres (31 mi) downstream, from Redgrave and Lopham fen, between Lowestoft and Beccles. Work was carried out to improve the ditch network at the site to prepare for the reintroduction and provide optimal habitat for the new spider population. [21] [22]

Castle Marshes nature reserve, the site of the first great raft spider reintroduction in the UK Castle marshes nature reserve.jpg
Castle Marshes nature reserve, the site of the first great raft spider reintroduction in the UK

The spiderlings were bred from adults from both the Redgrave and Lopham fen and Pevensey Levels subpopulations. This was to increase the genetic variability of the new population and increase its chances of survival. Each spiderling was hand reared in separate test tubes and fed with fruit flies. If the new population successfully establishes itself it will be one of only four great raft spider populations in the UK. Another population of spiders was also introduced at the same time to Redgrave and Lopham fen to support the small population already present. [10] [23]

As of 2024, the spiders are reportedly making a comeback, particularly in East Anglia. [24]

Norway

In July 2013, a wildlife enthusiast found a suspected specimen in Rakkestad, Østfold County in Norway. Several experts have confirmed the descriptions as belonging to the great raft spider. This would make it the first confirmed sighting of the species within Norway. [25]

Related Research Articles

<span class="mw-page-title-main">National nature reserves in England</span>

National nature reserves in England are designated by Natural England as key places for wildlife and natural features in England. They were established to protect the most significant areas of habitat and of geological formations. NNRs are managed on behalf of the nation, many by Natural England itself, but also by non-governmental organisations, including the members of The Wildlife Trusts partnership, the National Trust, and the Royal Society for the Protection of Birds.

National nature reserves in Suffolk, England are established by Natural England and managed by them or by non-governmental organisations such as the Royal Society for the Protection of Birds, the National Trust or the Suffolk Wildlife Trust.

<span class="mw-page-title-main">Redgrave and Lopham Fens</span> Nature reserve in Norfolk and Suffolk, England

Redgrave and Lopham Fens is a 127 hectare biological Site of Special Scientific Interest between Thelnetham in Suffolk and Diss in Norfolk. England. It is a national nature reserve, a Ramsar internationally important wetland site, a Nature Conservation Review site, Grade I, and part of the Waveney and Little Ouse Valley Fens Special Area of Conservation. It is managed by the Suffolk Wildlife Trust.

<span class="mw-page-title-main">Nursery web spider</span> Family of spiders

Nursery web spiders (Pisauridae) are a family of araneomorph spiders first described by Eugène Simon in 1890. Females of the family are known for building special nursery webs. When their eggs are about to hatch, a female spider builds a tent-like web, places her egg sac inside, and stands guard outside, hence the family's common name. Like wolf spiders, however, nursery web spiders are roaming hunters that do not use webs for catching prey.

<span class="mw-page-title-main">Suffolk Wildlife Trust</span>

Suffolk Wildlife Trust (SWT) describes itself as the county's "nature charity – the only organisation dedicated wholly to safeguarding Suffolk's wildlife and countryside." It is a registered charity, and its headquarters is at Brooke House in Ashbocking, near Ipswich. It was founded in 1961, and is one of 46 wildlife trusts covering the Great Britain and Northern Ireland. As of March 2017, it has 13,200 members, and it manages 3,120 hectares of land in 60 nature reserves, most of which are open to the public. It had an income of £3.9 million in the year to 31 March 2017.

<i>Dolomedes</i> Genus of spiders

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 D. albineus of the southeastern United States. Many species have a striking pale stripe down each side of the body.

<span class="mw-page-title-main">Raft spider</span> Species of spider

The raft spider, scientific name Dolomedes fimbriatus, is a large semi-aquatic spider of the family Pisauridae found throughout north-western and central Europe. It is one of only two species of the genus Dolomedes found in Europe, the other being the slightly larger Dolomedesplantarius which is endangered in the UK.

<span class="mw-page-title-main">Crymlyn Bog</span> Site of Special Scientific Interest in Wales

Crymlyn Bog is a nature reserve and a designated Site of Special Scientific Interest of international significance, near Swansea, south Wales.

<span class="mw-page-title-main">Kauaʻi cave wolf spider</span> Species of spider

The Kauaʻi cave wolf spider, also known to local residents as the blind spider, is only known to occur in a few caves in a lava flow with an area of 10.5 km2 (4.1 sq mi) in the Kōloa–Poʻipū region of Kauaʻi, Hawaiian Islands, and only six populations are known to exist. While their nearest surface-dwelling relatives have large eyes, this species has completely lost its eyes. They reach a body length around 20 mm (0.8 in), and are reddish brown and completely harmless to people. Unlike most wolf spiders, it produces only 15 to 30 eggs per clutch. The female carries the egg sac in her mouthparts until the spiderlings hatch.

<i>Dolomedes minor</i> Species of spider

Dolomedes minor is a spider in the family Pisauridae that is endemic to New Zealand, where it is known as the nursery web spider.

Grazing marsh is a British Isles term for flat, marshy grassland in polders. It consists of large grass fields separated by fresh or brackish ditches, and is often important for its wildlife.

The Little Ouse Headwaters Project (LOHP) was set up in 2002 by local residents to promote conservation and enjoyment of the fenland habitats bordering the upper reaches of the River Little Ouse, which lies on the Norfolk-Suffolk border. The site lies between Blo' Norton in Norfolk and Thelnetham in Suffolk. It includes a number of areas including Hinderclay Fen, Blo' Norton Fen, Betty's Fen, The Frith, Blo' Norton Lowes, Blo' Norton Little Fen and Parker's Piece. The area also include parts of the Blo' Norton and Thelnetham Fen Site of Special Scientific Interest (SSSI).

<i>Dolomedes aquaticus</i> Species of spider

Dolomedes aquaticus is a species of fishing spider that lives and hunts along the gravel banks of unforested New Zealand rivers. It prefer open riverbanks where it typically lives under rocks, usually less than 5 metres away from the river. Its colouring allows it to camouflage against river stones. Normally nocturnal, it will sit and wait for prey after dark, and can survive for short periods under the water.

<span class="mw-page-title-main">Sound Heath</span> Area of common land in Sound, Cheshire, England, UK

Sound Heath, also known as Sound Common, is an area of common land in Sound, near Nantwich in Cheshire, England, which includes heathland, grassland, scrub, woodland and wetland habitats. The majority of the area is designated a Site of Special Scientific Interest and a Local Nature Reserve.

<span class="mw-page-title-main">Six-spotted fishing spider</span> Species of spider

The six-spotted fishing spider is an arachnid from the nursery web spider family Pisauridae. This species is from the genus Dolomedes, or the fishing spiders. Found in wetland habitats throughout North America, these spiders are usually seen scampering along the surface of ponds and other bodies of water. They are also referred to as dock spiders because they can sometimes be witnessed quickly vanishing through the cracks of boat docks. D. triton gets its scientific name from the Greek mythological god Triton, who is the messenger of the big sea and the son of Poseidon.

<i>Pisaurina mira</i> Species of spider

Pisaurina mira, also known as the American nursery web spider, due to the web it raises young in, is a species of spider in the family Pisauridae. They are often mistaken for wolf spiders (Lycosidae) due to their physical resemblance. P. mira is distinguished by its unique eye arrangement of two rows. 

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Barnby Broad and Marshes is a Site of Special Scientific Interest (SSSI) in the Waveney district of the English county of Suffolk. The site is 189.6 hectares in size. It is in the parishes of North Cove and Barnby, located between Beccles and Lowestoft in the north of the county. The site is bordered on its southern edge by the East Suffolk railway line and to the north by the River Waveney. It is a Special Area of Conservation, a Special Protection Area under the EC Birds Directive, and a Ramsar internationally important wetland site. There are two Suffolk Wildlife Trust nature reserves in the site, Castle Marshes and North Cove.

<span class="mw-page-title-main">Blo' Norton and Thelnetham Fens</span>

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<i>Dolomedes schauinslandi</i> Species of spider

Dolomedes schauinslandi or the Rangatira spider is a large spider of the family Pisauridae. It is only found on South East Island (Rangatira), Houruakopara and Mangere Islands in the Chatham Islands, New Zealand. It is one of New Zealand's largest and rarest spiders.

References

  1. 1 2 3 World Conservation Monitoring Centre (1996). "Dolomedes plantarius". IUCN Red List of Threatened Species . 1996: e.T6790A12806270. doi: 10.2305/IUCN.UK.1996.RLTS.T6790A12806270.en . Retrieved 17 November 2021.
  2. 1 2 "Taxon details Dolomedes plantarius (Clerck, 1757)". World Spider Catalog. Natural History Museum Bern. Retrieved 2017-09-13.
  3. ↑ "Dolomedes plantarius". Fauna Europaea. Archived from the original on June 22, 2011. Retrieved 2010-01-16.
  4. ↑ "The World Spider Catalog, Version 10.5 - FAM. PISAURIDAE". American Museum of Natural History . Retrieved 2010-01-16.
  5. 1 2 "Fen raft spider (Dolomedes plantarius)". Arkive. Archived from the original on 2009-12-28. Retrieved 2010-01-16.
  6. 1 2 3 4 "Biology of D.plantarius (Clerk)". dolomedes.org.uk. Archived from the original on 2010-01-22. Retrieved 2010-01-16.
  7. ↑ "The fen raft spider". Suffolk Wildlife Trust. Archived from the original on 2006-05-24. Retrieved 2010-01-16.
  8. ↑ "European distribution of D.plantarius (Clerk)". dolomedes.org.uk. Archived from the original on 2010-01-23. Retrieved 2010-01-16.
  9. ↑ Naumova, Maria. (2018). Review of the Distribution of the Genus Dolomedes Latreille, 1804 (Araneae: Pisauridae) on the Balkan Peninsula, with New Records from Bulgaria. Acta Zoologica Bulgarica. 70. 479-486.
  10. 1 2 "Return to the Fens for one of the UK's rarest spiders". Natural England. Archived from the original on 2012-02-12. Retrieved 2010-11-15.
  11. 1 2 "D. plantarius populations in the UK". dolomedes.org.uk. Archived from the original on 2010-01-23. Retrieved 2010-01-16.
  12. ↑ Latham FA, ed. Acton, p. 127 (The Local History Group; 1995) ( ISBN   0 9522284 1 6)
  13. 1 2 3 "Species Action Plan Fen Raft Spider (Dolomedes plantarius)". Joint Nature Conservation Committee. Archived from the original on 2007-10-28. Retrieved 2010-01-16.
  14. ↑ "Giant spiders the size of rats making a comeback in UK". The Independent. 18 August 2024.
  15. 1 2 3 "Targets - 'Dolomedes plantarius (Fen Raft Spider)". Biodiversity Action Reporting System. Retrieved 2010-01-16.
  16. ↑ "2006 Summary Report for Redgrave and Lopham Fen" (PDF). Fen Raft Spider Recovery Project. Retrieved 2009-01-07.
  17. ↑ "Status - Dolomedes plantarius (Fen Raft Spider)". Biodiversity Action Reporting System. Retrieved 2010-01-16.
  18. ↑ "Fish-eating spider invades Wales". BBC News. 2003-08-14. Retrieved 2010-01-16.
  19. ↑ "Trends - Dolomedes plantarius (Fen Raft Spider)". Biodiversity Action Reporting System. Archived from the original on 2010-11-09. Retrieved 2010-01-16.
  20. ↑ "Spiderlings to descend on Suffolk broads". BBC News. 2010-10-21. Retrieved 2010-11-15.
  21. ↑ "Over a thousand rare spiders released on Suffolk Broads". Suffolk Wildlife Trust. Archived from the original on 2011-07-28. Retrieved 2010-11-15.
  22. ↑ Rare spiders set up home on nature reserve by Lowestoft- with help of Redgrave and Lopham Fen Archived 2014-02-22 at the Wayback Machine , Eastern Daily Press, 2012-07-09. Retrieved 2013-01-25.
  23. ↑ Aburawa, Arwa (2010-10-22). "Hand-reared endangered spiders released into the wild". The Guardian . London. Retrieved 2010-11-15.
  24. ↑ "Giant spiders the size of rats making a comeback in UK". The Independent. 2024-08-18. Retrieved 2024-08-18.
  25. ↑ "Rare spider found in Norway / News / The Foreigner — Norwegian News in English". Archived from the original on 2014-02-22. Retrieved 2013-09-24.
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