''Dolomedes aquaticus'' is a

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

that lives and hunts along the gravel banks of unforested

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

rivers. It prefers open riverbanks where it lives under rocks, usually less than 5 metres from the river. Its colouring allows it to blend in with river stones. Normally nocturnal, it sits and waits for its prey after dark, and can survive for short periods under the water.

Taxonomy

''Dolomedes aquaticus'' was described in 1887 by Peter Goyen.

Description

Females have a total body length of 13–26 mm, males being smaller at 11–18 mm. The fourth leg is longest, about 36 mm in females and 33 mm in males. The

cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

is chocolate brown, with a supra-marginal band of yellow extending from the posterior slope to the anterior angle of the pars cephalica: falces, maxillæ, labium, and sternum chocolate-brown; legs and palpi, brown; abdomen above greenish-brown with two longitudinal rows of brown-margined yellow spots, at the sides greyish, and below dusky-brown with four more or less continuous longitudinal whitish stripes converging towards the anus. At the base of the dorsal surface there is a short median spathulate band of paler hue than the rest of that surface, and on each side of this band a short grey fleck. The cephalothorax and abdomen are densely covered with grey, yellow, and brown pubescence.

Habitat/Distribution

''Dolomedes aquaticus'' occurs on open, stony riverbeds and also rocky lake shorelines. ''D. aquaticus'' has been observed to be at its highest abundance when there was intermediate disturbance along the river banks. ''D. aquaticus'' can be found throughout the

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

of New Zealand and in the lower half of the

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-largest ...

of New Zealand.It has been suggested that ''D. aquaticus'' is not present in the upper half of the North Island due to the lack of

braided rivers A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment lo ...

in this region.

Behaviour

''Dolomedes aquaticus'' is found on plants, stones, or pieces of wood at or near the surface of the water. It can swim and run very rapidly on the surface of the water. When teased it makes for the nearest object, down which it runs to the bottom of the water, where it remains till all danger has gone. While incubating, the female goes some distance from the water, and lives under a large stone or a piece of wood. Here she remains till the young are hatched. During incubation she shows considerable aversion to water. The cocoon is globular, and is carried under the sternum, to which it is firmly held by the palpi and strands of web from the spinners.

References

* Simon Pollard
Spiders and other arachnids
''Te Ara - the Encyclopedia of New Zealand'', updated 21-Sep-2007. {{Taxonbar, from=Q2661102 aquaticus Spiders of New Zealand Spiders described in 1887