158 SPIDERS 



in A.ferox is almost double that of A. similis. A. similis 'tires' very 

 rapidly when forced to run at full speed without stopping and is 

 almost always overcome in fights between evenly matched indi- 

 viduals of the two species. Both species can run for long periods 

 when supplied with oxygen and it is suggested that the greater 

 stamina oi A.ferox depends upon a proportionately larger respira- 

 tory surface acquired at the expense of greater dependence upon 

 environmental humidity (Cloudsley-Thompson, 1957). 



In Britain, and in fact in the whole of the northern hemisphere, 

 there is only one spider that is truly aquatic. This is the well-known 

 Argyroneta aquatica, one of our largest species and somewhat ex- 

 ceptional in that the male is bigger than its mate. It swims under 

 water clothed in a bubble of air that shines like quicksilver, and 

 constructs a retreat in the form of a diving bell of silk filled with air 

 which is carried down in bubbles from the surface. There are, 

 however, several other species which live, like fishermen, by and 

 on the water. Although most wolf spiders frequent dry and stony 

 places and are particularly numerous in spring and early summer, 

 the members of the genus Pirata are semi-aquatic, living at the 

 margins of rivers and ponds, and are able to run on the surface of 

 the water. P. piscatorius spins a silken tube in moss at the water's 

 edge and will run beneath the water if it is alarmed. As the incom- 

 ing tide creeps over the mud flats, Lycosa purbeckensis, an inhabi- 

 tant of salt marshes, touches the water 'like a bather feeling the 

 temperature with his toe before taking the plunge', and then 

 deliberately walks down the stem of a sedge or other halophytic 

 plant, taking with it a bubble of air caught by means of the hairs on 

 its body (Bristowe, 1923). Various Theridiidae, such as Oedo- 

 thorax fuscus and species of Desis ( Agelenidae) from the shores of 

 the Indian ocean, also live under semi-marine conditions. 



To escape capture, the large Dolomedes fimbriatus (Pisauridae) 

 will run down a plant stem beneath the surface of the water. This 

 species, which lives in swamps and ditches, is sometimes called the 

 'raft-spider' on account of a popular fallacy that it makes a raft of 

 fallen leaves on which to float downstream. Some of its foreign 

 relations catch tadpoles and even small fishes to eat. No obvious 

 features indicate that the Pisauridae are spiders of the water, but 

 they can run on the surface with a grace almost equalling that of a 



