INSECTS AND DISEASE. 



343 



Finally, we must at least mention that in ants, bees, 

 wasps, and termites we find illustration of various grades of 

 social life, and marvellous exhibitions of instinctive skill as 

 well as some intelligence. 



INSECTS AND DISEASE. 



As carriers of disease-germs insects play a very im- 

 portant part. The role of flies as mechanical distributors 

 of anthrax, plague, and other bacterial diseases has been 

 clearly proved. Besides carrying bacilli upon their bodies 

 and leaving them on wounds or food, they also swallow 



Fir,. 169. Mosquito. 



germs, and subsequently deposit them in their excreta in 

 similar situations. Undoubtedly, however, the most serious 

 cases are those of the blood-sucking Diptera which act as 

 hosts as well as carriers of disease producing parasites. 

 The gnats or mosquitoes (Culicidas) are perhaps the most 

 important in this respect. Human malaria is conveyed by 

 at least twelve different species of mosquito, of which those 

 belonging to the genus Anopheles have the widest dis- 

 tribution. Anopheles maculipennis occurs all over Europe, 

 in many parts of Africa, North America, and India, 

 and in all these countries it carries malaria (see Fig. 161). 

 Proteosoma, the malaria parasite of birds, is carried by a 

 Culex, a related genus. The unknown parasite of yellow 



