226 



LAKES AND RIVERS, 



growth of the barren stems of the Equisetum comes 

 also in summer. On the banks of the Ouse I once 

 saw a wild duck's nest in this month. 



April is still more conspicuous for the variety of its 

 fauna and flora. The water-net enables us to capture 

 a multitude of insects; among the most abundant 

 are the water-scorpion (Nepa dnerea). This insect 

 is of a gray-black colour, red underneath. Its 

 front legs have great prehen- 

 sile power, and with them it 

 seizes its insect prey, which it 

 sucks with its strong rostrum 

 or beak. The rostrum con- 

 tains three joints and four 

 pointed bristles; two have a 

 sharp blade, and have teeth 

 towards their base. Of the 

 others, one is like a thin 

 needle, the other is provided 

 with hairs directed backwards 

 and forwards. The apparatus 



may be compared with that of a surgeon's cupping 

 instrument, and its bite is painful to man. 



One of the most remarkable of the inhabitants of 

 these ditches is undoubtedly the water diving-spider 

 (Argyoneta aquatica), which weaves a curious bell- 

 shaped net beneath the water, to which it carries its 

 prey. It fills this bell with air, which causes it to 

 assume a silvery appearance. The air is carried 

 down entangled in the hairs of the spider, suggests 

 the method by which diving-bells among men were 

 formerly supplied with air. 



WATER-SCORPION. 



