Dolomedes is a genus of large spiders of the family Dolomedidae. 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; then injecting venom with their hollow chelicerae 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 which means wily, deceitful.LSJ: δολομήδης
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 .Animal Diversity Web: Dolomedes triton
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 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. They can be differentiated from wolf spiders by their smaller posterior median eyes, and eye arrangement of eight eyes in two rows as opposed to three rows. If this is insufficient, 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.University of Arkansas Museum Arthropod Museum web page: dark fishing spider (Dolomedes tenebrosus). 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 in New Zealand is aquatic insects,Greenwood, Michelle, 2008. "Aquatic Assassins: The Secret Life of Fishing Spiders". New Zealand Geographic, 91. (online summary ) but they are opportunistic feeders and will eat anything suitable that happens within range. There are reports in Australia of Dolomedes, including a Dolomedes facetus, eating goldfish and a report in the United States of a Dolomedes consuming an immature smallmouth bass, but more common prey may be Gambusia species, sticklebacks, Elassoma and other small fish depending on locale.
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