Dolomedes Sumatranus

''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.

They hunt by waiting at the edge of a pool or stream, then when they detect the ripples from prey, they run across the surface to subdue it using their foremost legs, which are tipped with small claws; like other spiders they then inject venom with their hollow jaws to kill and digest the prey. They mainly eat insects, but some larger species are able to catch small fish. They can also climb beneath the water, when they become encased in a silvery film of air. "''Dolomedes''" is derived from the Greek word "δολομήδης" which means wily, deceitful.

There are over a hundred species of ''Dolomedes'' throughout the world; examples include ''Dolomedes aquaticus'', a forest-stream species of New Zealand, the raft spider (''D. fimbriatus''), which lives in bogs in Europe, and the great raft spider (''D. plantarius''), which lives in fens, also in Europe. Many species are large, some with females up to long with a leg span of .

Aquatic adaptations

''Dolomedes'' spiders are covered all over in short, velvety hairs which are hydrophobic. This allows them to use surface tension to stand or run on the water, like water striders. They can also climb beneath the water, and then air becomes trapped in the body hairs and forms a thin film over the whole surface of the body and legs, giving them the appearance of fine polished silver. Like other spiders, ''Dolomedes'' breathe with book lungs beneath their abdomens, and these open into the air film, allowing the spiders to breathe while submerged. The trapped air makes them very buoyant and even if they do not hold onto a rock or a plant stem they float to the surface where they pop onto the surface film, completely dry.

Identification

If any of this species are seen without context, one may confuse them with the family Lycosidae, otherwise known as Wolf Spiders. Though one could easily identify them, as this genus owns 2 rows of eyes, with 2 larger eyes at the top, which is unique to this genus inside the Pisauridae family. If this isn't sufficient, one can further differentiate them thanks to their aquatic adaptations.

Hunting behavior

Rather than hunting on land or by waiting in a web, these spiders hunt on the surface of the water itself, preying on mayflies, other aquatic insects, and even small fish. For fishing spiders, the water surface serves the same function as a web does for other spiders. They extend their legs onto the surface, feeling for vibrations given off by prey.

''Dolomedes'' are nocturnal hunters, feeding when birds, their main predators, are sleeping. The method they use to fish for insects is to hold on to the shore with their back legs while the rest of their body lies on the water, with legs stretched out. ''Dolomedes'' species tend to be robust with thickset legs that allow them to tackle prey larger than themselves. They stretch out their front legs and wait, as if listening. Their front legs feel the vibrations carried on the water, just as other spiders feel the vibrations in a web. They are able to tell what is causing the vibrations that the water is carrying - to distinguish the drawn-out, erratic vibrations of a struggling insect from the one-off vibrations caused by falling leaves or the background noise of the wind or the flow of the water around rocks and other obstacles. As well as identifying the source of the vibrations, the spiders are also able to discern the distance to and direction of the source. To this end they have a range of vibration-detecting organs, including very sensitive hairs (trichobothria) on their legs and feet. Their eyes play a secondary role - experiments on related species show that touch is the main sense these spiders use to catch their prey. Their eyes are of little use for nocturnal hunting. These vibration detectors also serve to warn the spider of predators such as trout.

As soon as the vibrations reveal that there is a floundering insect within range, some fishing spiders may take direct action - they run at pace across the surface of the water and grab the insect before it extracts itself from the water and flies to safety. Some fishing spiders use silk draglines to prevent themselves from speeding past the prey.

Fishing spiders' main prey is aquatic insects, but they are opportunistic feeders and will eat anything suitable that happens within range. ''Dolomedes'' in North America have been observed catching and eating small goldfish.Greenwood, Michelle, 2008. Aquatic Assassins: The Secret Life of Fishing Spiders. ''New Zealand Geographic'', 91.
online summary
).

Predators

The main predators of fishing spiders are birds and snakes. Dragonflies have also been observed catching young spiders. Species parasitic on the spiders include a wasp of the Pompilidae family, commonly called the Spider Wasp, that stings the spider to paralyze it before carrying it off and laying an egg in its abdomen. The larvae of the wasp hatch and proceed to eat the spider from the inside out. One escape technique the spiders use is to disappear beneath the surface tension of the water. However, some wasps, such as ''Anoplius depressipes'', are able to be underwater for a few minutes to sting the spider and drag it out of the water.

Breeding

The males outnumber the females 3:1 suggesting a male-biased sex ratio. Mating in one North American species (''D. tenebrosus'') always results in the obligate death of the male, with no obvious involvement from the female."Spontaneous male death and monogyny in the dark fishing spider", Steven K. Schwartz, William E. Wagner Jr and Eileen A. Hebets. Biol. Lett. 23 August 2013 vol. 9 no. 4 20130113. http://rsbl.royalsocietypublishing.org/content/9/4/20130113.long

Species

, the World Spider Catalog accepted the following 101 species:

*''Dolomedes actaeon'' Pocock, 1903 – Cameroon
*'' Dolomedes albicomus'' L. Koch, 1867 – Australia (Queensland, New South Wales)
*''Dolomedes albicoxus'' Bertkau, 1880 – Brazil
*''Dolomedes albineus'' Hentz, 1845 – USA
*''Dolomedes alexandri'' Raven & Hebron, 2018 – Australia (Capital Territory, Victoria)
*'' Dolomedes angolensis'' (Roewer, 1955) – Angola
*'' Dolomedes angustivirgatus'' Kishida, 1936 – China, Korea, Japan
*'' Dolomedes angustus'' (Thorell, 1899) – Cameroon
*'' Dolomedes annulatus'' Simon, 1877 – Philippines
*''Dolomedes aquaticus'' Goyen, 1888 – New Zealand
*'' Dolomedes batesi'' Pocock, 1903 – Cameroon
*''Dolomedes bistylus'' Roewer, 1955 – Congo
*'' Dolomedes boiei'' (Doleschall, 1859) – Sri Lanka, Indonesia (Java)
*'' Dolomedes briangreenei'' Raven & Hebron, 2018 – Australia (New South Wales, Queensland)
*''Dolomedes bukhkaloi'' Marusik, 1988 – Russia
*'' Dolomedes chevronus'' Yin, 2012 – China
*'' Dolomedes chinesus'' Chamberlin, 1924 – China
*''Dolomedes chroesus'' Strand, 1911 – Indonesia (Aru Is., New Guinea)
*'' Dolomedes costatus'' Zhang, Zhu & Song, 2004 – China
*'' Dolomedes crosbyi'' Lessert, 1928 – Congo
*'' Dolomedes dondalei'' Vink & Dupérré, 2010 – New Zealand
*''Dolomedes elegans'' Taczanowski, 1874 – French Guiana
*''Dolomedes facetus'' L. Koch, 1876 – Australia, New Guinea, Samoa
*'' Dolomedes fageli'' Roewer, 1955 – Congo
*''Dolomedes femoralis'' Hasselt, 1882 – Indonesia (Sumatra)
*'' Dolomedes fernandensis'' Simon, 1910 – Equatorial Guinea (Bioko)
*''Dolomedes fimbriatus'' (Clerck, 1757) (type species) – Palearctic
*'' Dolomedes flaminius'' L. Koch, 1867 – Australia (Queensland), New Caledonia
*''Dolomedes fontus'' Tanikawa & Miyashita, 2008 – Japan
*'' Dolomedes furcatus'' Roewer, 1955 – Mozambique
*''Dolomedes fuscipes'' Roewer, 1955 – Cameroon
*''Dolomedes fuscus'' Franganillo, 1931 – Cuba
*'' Dolomedes gertschi'' Carico, 1973 – USA
*''Dolomedes gracilipes'' Lessert, 1928 – Congo
*''Dolomedes guamuhaya'' Alayón, 2003 – Cuba
*''Dolomedes holti'' Carico, 1973 – Mexico
*''Dolomedes horishanus'' Kishida, 1936 – Taiwan, Japan
*'' Dolomedes instabilis'' L. Koch, 1876 – Australia, Papua New Guinea
*'' Dolomedes intermedius'' Giebel, 1863 – Colombia
*''Dolomedes japonicus'' Bösenberg & Strand, 1906 – China, Korea, Japan
*''Dolomedes kalanoro'' Silva & Griswold, 2013 – Madagascar
*'' Dolomedes karijini'' Raven & Hebron, 2018 – Australia (Western Australia)
*'' Dolomedes karschi'' Strand, 1913 – Sri Lanka
*'' Dolomedes lafoensis'' Berland, 1924 – New Caledonia
*''Dolomedes laticeps'' Pocock, 1898 – Solomon Is.
*''Dolomedes lesserti'' Roewer, 1955 – Mozambique
*''Dolomedes lizturnerae'' Raven & Hebron, 2018 – Australia (Tasmania)
*''Dolomedes machadoi'' Roewer, 1955 – West Africa
*''Dolomedes macrops'' Simon, 1906 – Sudan
*''Dolomedes mankorlod'' Raven & Hebron, 2018 – Australia (Northern Territory)
*'' Dolomedes mendigoetmopasi'' Barrion, 1995 – Philippines
*''Dolomedes minahassae'' Merian, 1911 – Indonesia (Sulawesi)
*''Dolomedes minor'' L. Koch, 1876 – New Zealand
*'' Dolomedes mizhoanus'' Kishida, 1936 – China, Laos, Malaysia, Taiwan
*''Dolomedes naja'' Berland, 1938 – Vanuatu
*''Dolomedes neocaledonicus'' Berland, 1924 – New Caledonia
*'' Dolomedes nigrimaculatus'' Song & Chen, 1991 – China, Korea
*''Dolomedes noukhaiva'' Walckenaer, 1847 – Marquesas Is.
*'' Dolomedes ohsuditia'' Kishida, 1936 – Japan
*''Dolomedes okefinokensis'' Bishop, 1924 – USA
*''Dolomedes orion'' Tanikawa, 2003 – Japan
*''Dolomedes palmatus'' Zhang, Zhu & Song, 2005 – China
*''Dolomedes palpiger'' Pocock, 1903 – Cameroon
*''Dolomedes paroculus'' Simon, 1901 – Malaysia
*'' Dolomedes pedder'' Raven & Hebron, 2018 – Australia (Tasmania)
*'' Dolomedes pegasus'' Tanikawa, 2012 – Japan
*''Dolomedes petalinus'' Yin, 2012 – China
*''Dolomedes plantarius'' (Clerck, 1757) – Europe, Russia (Europe to South Siberia), Kazakhstan
*'' Dolomedes pullatus'' Nicolet, 1849 – Chile
*'' Dolomedes raptor'' Bösenberg & Strand, 1906 – Russia, China, Korea, Japan
*''Dolomedes raptoroides'' Zhang, Zhu & Song, 2004 – China
*'' Dolomedes saganus'' Bösenberg & Strand, 1906 – China, Taiwan, Japan
*''Dolomedes schauinslandi'' Simon, 1899 – New Zealand
*''Dolomedes scriptus'' Hentz, 1845 – USA, Canada
*''Dolomedes senilis'' Simon, 1880 – Russia, China, Japan
*''Dolomedes signatus'' Walckenaer, 1837 – Mariana Is.
*'' Dolomedes silvicola'' Tanikawa & Miyashita, 2008 – China, Japan
*'' Dolomedes smithi'' Lessert, 1916 – East Africa
*'' Dolomedes spathularis'' Hasselt, 1882 – Indonesia (Sumatra)
*''Dolomedes stilatus'' Karsch, 1878 – Australia
*''Dolomedes straeleni'' Roewer, 1955 – Congo
*''Dolomedes striatus'' Giebel, 1869 – USA, Canada
*'' Dolomedes sulfureus'' L. Koch, 1878 – Russia, China, Korea, Japan
*'' Dolomedes sumatranus'' Strand, 1906 – Indonesia (Sumatra)
*''Dolomedes tadzhikistanicus'' Andreeva, 1976 – Tajikistan
*''Dolomedes tenebrosus'' Hentz, 1844 – USA, Canada
*'' Dolomedes titan'' Berland, 1924 – New Caledonia, Vanuatu
*''Dolomedes toldo'' Alayón, 2003 – Cuba
*'' Dolomedes transfuga'' Pocock, 1900 – Congo
*''Dolomedes triton'' (Walckenaer, 1837) – North America, Cuba
*''Dolomedes upembensis'' (Roewer, 1955) – Congo
*''Dolomedes vatovae'' Caporiacco, 1940 – Ethiopia
*''Dolomedes venmani'' Raven & Hebron, 2018 – Australia (New South Wales, Queensland)
*'' Dolomedes vicque'' Raven & Hebron, 2018 – Australia (Victoria, New South Wales, Queensland)
*'' Dolomedes vittatus'' Walckenaer, 1837 – USA
*'' Dolomedes wetarius'' Strand, 1911 – Indonesia
*'' Dolomedes wollastoni'' Hogg, 1915 – New Guinea
*''Dolomedes wollemi'' Raven & Hebron, 2018 – Australia (New South Wales)
*'' Dolomedes yawatai'' Ono, 2002 – Japan (Ryukyu Is.)
*''Dolomedes zatsun'' Tanikawa, 2003 – Japan
*''Dolomedes zhangjiajiensis'' Yin, 2012 – China

Distribution

The approximately 100 species of ''Dolomedes'' have a worldwide distribution. The largest number of species are found in Asia, with particularly high species diversity in South-east Asia, from China and Japan to New Guinea. The second largest number of species occur in tropical Africa. South America has only four species.

North America

Nine species of ''Dolomedes'' exist in North America. The six-spotted fishing spider ('' D. triton'') lives primarily in small lakes and ponds. This spider consumes mostly water striders (pond skaters), but like all ''Dolomedes'', it is an opportunistic ambush hunter that will eat anything that it can capture. Other species include the bog-dwelling '' D. striatus'', and four species living by streams: '' D. scriptus'', '' D. vittatus'', '' D. gertschi'' and '' D. holti''. Two North American species, '' D. tenebrosus'' and '' D. okefinokensis'', exhibit female giganticism and/or male dwarfism, with their males being less than half the size of the females. The ninth species is the arboreal '' D. albineus''.

Europe

Two ''Dolomedes'' species occur in Europe (excluding Russia). The Palearctic raft spider (''D. fimbriatus'') is widespread on the surface of bog pools and in boggy grassland. The great raft spider (''D. plantarius'') lives in fens, and is listed as endangered in Great Britain and is globally vulnerable.

New Zealand

Four endemic species of ''Dolomedes'' occur in New Zealand, three on the mainland and one on the Chatham Islands. Two are widespread: '' D. aquaticus'' of open riverbanks and lakeshores, and '' D. dondalei'' or New Zealand forest fishing spider (once referred to as ''Dolomedes'' III), which specialises in forested riverbanks. The largest New Zealand species, '' D. schauinslandi'' or the Rangatira spider, occurs on rodent-free islands in the Chathams where running water is rare. The fourth and most common species, '' D. minor'', is found in scrubland, grassland, and wetlands. It mostly hunts on the ground, but is still capable of catching aquatic prey. Known as the nursery web spider, it makes white nursery webs on shrubs.

References

Further reading

*Carico, James Edwin (1973): The Nearctic spiders of the genus ''Dolomedes'' (Araneae: Pisauridae). ''Bulletin of the Museum of Comparative Zoology (Harvard)'' 144 (7): 435-488.

External links

Fishing spider ''Dolomedes tenebrosus''(free for noncommercial use)


*Jeffrey K. Barnes

Arthropod Museum Notes, University of Arkansas.
*Richard Ford

Digitalwildlife.co.uk. image and short description

{{Taxonbar, from=Q2068864

Araneomorphae genera
Cosmopolitan spiders