Marvels of the Universe 



65 



THE WATER SPIDER 



BY R. I. POCOCK, F.R.S. 



Most people regard the di\ang-bell as exclusively a product of human invention. That is a mistake, 

 for, thousands of j-ears before man discovered this method of breathing and keeping dry under 

 water, there lived a species of spider which had solved precisely the same difficulty ; and this spider, 

 probably in \irtue of his clever invention, has survived to this day in our ponds and ditches. He 

 is commonly known as the Water-Spider, and technically by a Latin name which means the 

 " aquatic silver-swimmer." It is the appearance of this spider under water that has earned him 

 this name, for the hairs which cover the hinder-part of his body are long and hooked at the 

 end, and have the power of entangling the air when exposed to that element, so that the 

 animal, partially enveloped in a bubble, looks like a ball of quicksilver as it swims beneath the 

 surface. 



The bell, which the spider makes for its home, is a thimble-shaped case of silk, anchored by 

 threads to water-weeds, with the orifice turned downwards. To empty this bell of the water which 

 fills it, the spider disentangles the bubble of air inside the aperture and this, rising to the top of 

 the bell, displaces a certain amount of water. Another bubble is then fetched from the surface and 

 liberated in the same way ; and the operation is repeated until the bell is filled with air. This 

 provides a water-tight air chamber, and exhausted oxygen is made good by the same process of 

 bubble liberation. 



In this beU two batches of eggs are laid, one in the early summer and one in the autumn. The 

 summer eggs hatch quickly and the young soon start making diminutive bells on their own account ; 

 but after depositing the autumn batch, the mother closes up the mouth of the bell and passes the 

 winter in a dormant state with them, waiting for the warmth of spring to hatch them. At the 

 time of courtship, the male spins a bell alongside that of the female and makes a silk passage from 

 one to the other, so that he can pass into her bell without getting wet. Water-Spiders feed upon 

 aquatic insects and upon flies or gnats which alight on the surface of the water. 



Ptiolo by] 



THE HOVER-FLY. 



[/. J. Ward, 1:E.S. 

 5 



