INHABITANTS OF THE WATER-FILM 67 



waiting skater, the latter turns sharply towards it, and after 

 carefully polishing its beak makes an attack. On one occa- 

 sion an adult skater was seen to advance towards a struggling 

 fly, but before seizing its prey it very carefully cleaned and 

 brushed its beak with both its fore legs. Whilst so engaged in 

 preparation for the feast, a young and eager pond-skater turned 

 and saw the fly, and without more ado rushed forward and 

 captured it. Whether the adult realised the humour of the 

 situation it is difficult to say. 



The Gerridae seize their prey in a most interesting manner. 

 They place their front legs over the victim, and then elevating 

 their bodies, lift it well into their embrace. Now the beak 

 comes into action, and, as in the case of the gnat, a surgical 

 operation is rapidly performed, and the blood of the victim 

 extracted. 



Once having made a capture, Gerris is most unwilling, or 

 unable, to relinquish its hold, and will even leap as much as 

 an inch into the air, without dropping its victim. 



The ten British freshwater species are all very similar in 

 general appearance, but differ in size, and in the length of their 

 leg joints. Captured species often differ in the size of their 

 wings, because they are dimorphic that is to say, some of 

 the adults have two pairs of long wings, whilst others have 

 short wings ; but although the size may differ, one pair is always 

 leathery, whilst the other pair is membraneous. 



In summer pond-skaters congregate in large numbers, seem- 

 ingly socially inclined. On the approach of winter they hiber- 

 nate, and, in order to do so, wander some distance from their 

 usual habitat ; in fact it is recounted that a Gerris lacustris 

 was found sleeping under a fussbush in moss, half a mile from 

 the nearest pond. 



Although pond-skaters are very timid little beasts, yet they 

 are easily tamed, and, if looked after, will live and do well in 

 an aquarium. 



Velia currens, popularly known as the freshwater cricket, is 

 a more beautiful creature than the Gerris, but, similarly to the 

 latter, it lives on the water-film. Velia currens is a dark brown 

 insect, with two orange ridges along its back. Its movements 

 are noticeably different to those of Gerris, for whilst the latter, 

 as we have already seen, skates, Velia currens runs along the 

 water-film, and seems to find it difficult to make headway. In 

 certain localities are found minute black pond-skaters }% of 

 an inch in length. They are very interesting little creatures, 

 but unfortunately do not thrive in an aquarium. 



Mention must be made of Hydrometra stagnorum, which 



