FAMILY LIFE 207 



insects to hear the high-pitched hum of the females and to 

 direct their flight toward them. 



Few insects display more remarkable habits in courtship 

 than some predaceous two-winged flies of the family 

 Empidae, which have been studied by M. Howlett (1907) 

 and A. H. Hamm (1908-9). Empis borealts, a fairly large 

 species with russet brown wings, is common about mid- 

 summer in our hill-districts, and a number of females may 

 often be seen in " dancing " flight over the water of a 

 stream. A male with an insect such as a stonefly or a 

 mayfly captured as prey and carried in his legs, approaches, 

 and after flying up and down beneath one of the females 

 secures her and flies to some convenient plant-shoot. When 

 observed there, it is seen that the prey has been transferred 

 to the female by whom it is sucked during the process of 

 pairing. " The male," writes Howlett, '' usually hung by 

 the front pair of legs to a twig, or blade of grass, supporting 

 thus the whole weight of himself and partner ; the middle 

 legs clasped the thorax of the female, while the hind pair of 

 feet supported the prey in position beneath her proboscis, 

 the apical part of the femora meanwhile firmly compressing 

 her upturned abdomen. The hind legs of the female hung 

 idle while with the two front pairs she manipulated her 

 prey, kneading it as one who sucks an orange dry, and every 

 now and then turning it about to insert her beak in a fresh 

 spot." The males were never observed to suck the prey 

 which they caught nor did the females appear to catch any 

 insects for themselves. Hamm describes the methods of 

 capture practised by Empis tessellata : " the male sits in 

 wait upon a leaf or grass stem, darting upon any fly coming 

 near enough. If successful he immediately proceeds to 

 hang by the tarsal claw of one of the anterior legs to the 

 edge of a leaf or twig, the other five legs being tightly clasped 

 round the struggling victim. He then proceeds to feel 

 with the tip of the proboscis over the thorax of the fly, 

 finally reaching and immediately piercing the junction 

 between head and thorax. The proboscis was withdrawn 

 after a few seconds^ the victim being apparently paralysed 



