258 ANIMAL LIFE 



The black-fly (Simulium) illustrates the first ; the 

 hovering fly (Eristalis) the second. 



Simulium is a minute insect about one-seventh of 

 an inch in length, and appears to be a relative of 

 Ceratopogon if not closely allied to it. It is found in 

 marshy places, flying about in great swarms in a slow 

 and heavy manner, the fore-feet being kept in continual 

 movement, and evidently employed as feelers. Though 

 perfectly innocuous in this country, Simulium is one 

 of the greatest scourges to which man or beast is 

 exposed in Lapland, Hungary, the United States, and 

 Australia. Horses, cattle, and buffalo are especially 

 affected by this midge. A characteristic difference 

 separates the sexes. In the male the head is much 

 enlarged in consequence of the much greater develop- 

 ment of the eyes, the upper facets of which are larger 

 than the lower ones. The eyes of the female remain 

 small and undifferentiated into dimorphic facets. The 

 males swarm high in the air, whilst the females remain 

 at lower levels. Both sexes occur in the late spring, 

 and again in August. 



Simulium lays its eggs in gelatinous masses on 

 water plants that border rapid streams. The larvae 

 occur in clusters on leaves and stones, and are of such 

 curious form and habit as not readily to be taken for 

 insects. In appearance they resemble minute black 

 leeches. The cylindrical body is fixed by a terminal 

 sucker, in order to resist the current, and is provided 

 at its free or head-end with a second sucker and a pair 

 of revolving fans. When alarmed, the two suckers 



