254 INSECT WATER TRESPASSERS. 



As if to carry out the curious similitudes in art and 

 nature which have been indicated when mentioning 

 the resemblance of the water boatman to a keeled, and 

 the water beetle to a keel-less boat, the Whirlwig bears 

 an equally striking resemblance to the Welsh coracle, 

 its swimming legs also resembling paddles instead of 

 oars. 



The wings of the Whirlwig are large, and the 

 insect can use them with wonderful readiness, by 

 jumping out of the water by a violent jerk of the four 

 swimming legs, and instantly taking to wing. So 

 quickly is this done, that although the Whirlwigs are 

 continually darting into the air, they escape detection, 

 being mistaken for ordinary flies. The water boat- 

 man, by the way, can perform a similar feat, and when 

 it takes to wing, it produces a loud, deep, humming 

 sound like that of the hornet. It has quite a startling 

 effect if the insect should happen to pass close to the 

 ear. 



The peculiar eyes of the Whirlwig have often been 

 described. Generally, the compound eyes of the in- 

 sects are restricted to two clusters ; but in the Whirl- 

 wig they are again divided, so as to form four 

 clusters. Two of these occupy the usual position, and 

 are above the surface of the water when the insect 

 swims. The other pair are set almost on the under- 

 side of the head, and are, in consequence, always sub- 

 merged. 



Perhaps we may understand the position of the 

 eyes better by an illustration. The profile of the 

 Whirlwig's head bears a close resemblance to that of 

 a fish say a perch. If we then suppose that the 



