570 Animal Biology 



flies live on pollen and nectar of flowers, while the larvae eat plant 

 materials and other insects. The larvae of the ox-warble flies cause over 

 $100,000,000 damage annually by ruining the hides of cattle by boring 

 through the skin. The adult black flics are well-known pests because of 

 their blood-sucking habits. Every hunter, fisherman, and out-of-door 

 man has certainly been sufficiently annoyed to remember them well. 

 Mosquitoes (Fig. 303) of the genus Aedes transmit the virus of yellow 

 fever. Those of the genus Anopheles transmit the protozoa which cause 

 human malaria (Fig. 176). Only the females of these two species are 

 capable of carrying the germs because they suck blood, while the male 





Fig. 304. — Dog and cat flea {Ctenocephalus canis) of the order Siphonaptera. 

 a. Egg; h, larva in cocoon; c, pupa; d, adult; e, mouth parts of adult from side; 

 f, antenna; g, labium (lower lip) from below {h, c, and d, much enlarged; a, e, 

 f, and g, more enlarged). (From Howard: House Fleas, U. S. Department of 

 Agriculture; courtesy of Department of Entomology and Plant Quarantine.) 



probably feeds on the nectar of flowers. The females suck up the disease 

 germs from the blood of the patient ill with the disease. The germs 

 undergo part of their life cycle in the body of the insect and at the 

 proper time are injected into a susceptible person bitten by the germ- 

 carrying mosquito. The Hessian fly (one of the so-called gall gnats) 

 produces over $10,000,000 loss annually to the wheat crop in the United 

 States. The gall gnats deposit eggs in plant tissues. The eggs hatch into 

 larvae which irritate the plant so that the latter produces abnormal, 

 swollen enlargements known as galls (Fig. 271). Different types of galls 



