WATEE-SPIDEBS AND WATER-WOKMS. 275 



they have been upon the surface of tte water for a day, 

 they should be removed. 



While huntmg for specimens for the aquarium, one frequently 

 notices some curious little spider-like creatures less than |in. 

 long. They are often called " Water-spiders." This, how- 

 ever, is not a correct name to give them, for though they 

 are members of the oi-der Acarina, of the class Arachnida, 

 the title "Water-spider" properly belongs to their larger 

 relatives the Argyronetse, which have just been described. 

 These HydrachnidsB, or "Water-mites," are pretty, active 

 little creatures of various colours, and very suitable for 

 small aquaria. Some of them are able to swim freely about 

 the water, while others spend their time crawling over its 

 bottom or the aquatic weeds. The Water-mites are not 

 found in any great number, only two or three being as a 

 rule taken at one time; but they are by no means rare. 

 The Hydrachnidae, when mature, possess eight legs, affixed 

 to a body which may be said to be without segments or 

 division of any kind. The female Hydrachna lays her eggs 

 upon the stem of a water-plant. The young Mites which 

 come from these eggs are very different in foi-mation from 

 their parents. They have six legs, and not eight, and what 

 appears to be a large head, but which is better described as 

 a large suctorial apparatus. By means of this apparatus the 

 larvae are able to cling to larger aquatic animals, upon which 

 they live as parasites. They are not seldom found attached 

 to the upper part of the abdomen (beneath the elytra) of 

 the water-beetle {Dytiscus marginalis) or -to the long caudal 

 filaments of the water-scoi-pions (Banatra linearis and Nepa 

 cinerea). After living for a certain time as parasites, the 

 larvae become pupae, and pass then through a period of 

 inactivity before they make their final change and emerge 

 as perfect eight-legged Mites. The colours of full-grown 

 Mites are various, but generally they ai-e of bright red, 

 marked with black or brown spots. A magnifying-glass is 

 necessary to see the markings plainly. Hydrachnidae should 

 be kept in small glass vessels, in which there is a healthy 

 aquatic plant. They ai-e very predaceous, and ought to be 



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