314 ARTICULATA : INSECTA. 



Gnats or Musquitoes, lay their eggs in the water, and their 

 larvae may be seen in summer in all stagnant pools, where 

 they are popularly known as " wrigglers/' Tliey rest 

 with their head downward, and the hind extremity, which 

 contains the respiratory organs, is at such times at the 

 surface of the water. They are very active, and move 

 with a wriggling motion through the water, but come to 

 the surface from time to time to secure air through their 

 respiratory organs. At the end of their larval state they 

 shed their skin, but still remain in the water, and move 

 by means of their hind-body ; but now they assume a dif- 

 ferent attitude, and the respiration is carried on through 

 two tubes situated on the thorax. At the end of the pupa 

 state, which lasts only a few days, the skin splits upon the 

 back, between the breathing-tubes, and the winged insect 

 or imago appeal's, and after resting awhile on its empty 

 pupa-case as it floats upon the water, it flies away in search 

 of a victim whom it may pierce for blood. These kinds 

 of dipters discharge a poisonous fluid into the wounds 

 which they inflict, and this is the cause of the irritation 

 which follows their attacks. 



The larvae of some species of the Diptera, as the Hes- 

 sian Fly (Fig. 410) and the Wheat-fly (Cecidomyia tritici, 

 Kirby), are very injurious to the farmer, sometimes de- 

 stroying whole wheat-fields. ' 



Several species of the Diptera are very injurious or an- 

 noying to cattle and horses. One of these is known as the 

 Black Horse-fly (Tdbanus atratus, Fabricius), another as 

 the Orange-belted Horse-fly (T. cinctus, Fabr.), and an- 

 other the Lined Horse-fly (T. Urieola, Fabr.). All of these 

 have the eyes very large, covering nearly the whole head, 

 and they have a proboscis inclosing six sharp lancets in 

 the female, and four in the male. 



