102 



DIPTERA. 



of the wings. ,When flying in the early Spring, gnatsl 

 emit no sound. ''The warmer the weather, the greater 

 is their thirst for blood, the more forcible their flight, 

 the motion of the wings more rapid, and the sound 

 produced by that motion more intense." The two 

 most common house-inhabiting gnats are Culex 2npiens 

 (ciliaris) and C. annulatus. The genus Corethra is 



remarkable for the curi- 

 ous form and structure of 

 the larva. It is a long 

 worm-like creature as clear 

 as crystal ; the head is 

 furnished with tw^o de- 

 flexed hooks ; at the end 

 of the abdomen is a 

 fan of hairs ; unlike the 

 larva of Culex, the Corethra larva suspends itself in 

 a horizontal position in the water. There are two 



Pupa of Gxat {Corethra plumicornis). 



Larva of Gnat 'Corethra plumicornis), 



curious oblong vesicles of considerable size in the 

 thorax, and a pair of smaller ones towards the end of 

 the tail ; these organs are respiratory. The name of 

 Mosquito is sometimes applied to a SimtiUum, some- 

 times to a Culex. These insects are much more for- 

 midable pests in some countries than the species are 

 which are found in this country. Although the indi- 



