20 INSECTS AND HUMAN WELFARE 



malarial mosquitoes, as an expectation of relief from the 

 great personal discomfort of myriad mosquito bites exerts a 

 stronger appeal to the average person than the much more 

 important health problem of malaria. In the public mind, 

 the latter is unfortunately not usually regarded as so im- 

 mediately personal, as the fever and the bite are not co- 

 incident . 



At some time during the insect season, usually in the 

 spring, many districts are visited by swarms of small hump- 

 backed flies which viciously bite man and animals alike. On 

 account of their dark color these have been called black flies. 

 They pass their developmental stages almost entirely in 

 swiftly moving brooks and streams, where the larvae and 

 pupae are attached to stones and other objects in the water. 

 Wherever there are suitable streams in which they can breed, 

 these pests appear abundantly, and may be occasionally 

 present far from streams, where they would not be expected. 

 They are not known to be concerned in the transmission of 

 any disease. 



Minute flies, somewhat like mosquitoes, which are vicious 

 bloodsuckers, often appear in great abundance, particularly 

 in the cooler parts of the United States. These insects belong 

 to several genera, developing from aquatic larvse inhabiting 

 fresh water and also brackish water along the seacoast. 

 They are generally crepuscular, biting most abundantly at 

 dusk, and are persistent at that time, causing a stinging sen- 

 sation out of all proportion to their almost microscopic size. 

 None of our species are known to be disease carriers. 



The regions surrounding the Mediterranean Sea are the 

 centers of distribution for a very interesting, but not danger- 

 ous insect-borne disease known as phlebotomus fever. In 

 this case the carriers are minute gnat-like flies of the family 

 Psychodidae known as Phlebotomus. These insects are semi- 

 aquatic in the larval condition, occurring in damp situations, 

 drains, cellars, etc., where they feed on plant matter. The 

 adult is a vicious biter in spite of the fact that it is scarcely 

 over one millimeter in length. It rarely bites except at night, 



