CHAPTER VI 



DIPTEROUS LARV^ 



Flesh flies, blowflies, botflies. — The larvae of these flies produce a 

 form of parasitism to which the term myasis (also myiasis, and myiosis) 

 is applied. Various forms of myasis are recognized according to the 

 location of the larvae, as cutaneous, muscular, nasal, gastric, and intes- 

 tinal. With certain species, as those of the family CEstridae, or true 

 botflies, the lairval parasitism is obligate upon or within a living host 

 animal, while the larvae of the flesh and blowflies of the family Muscidae 

 may attack either living or dead, usually decomposing, tissue. 



Chrysomyia Macellaria 



Compsomyia macellaria; Cochliomyia macellaria, Screw worm fly.— 

 Muscidae (p. 37). Three-eighths to half an inch in length; color bluish 

 green with metallic reflections. There are three longitudinal black 

 stripes upon the thorax. The head is reddish or yellowish brown; 

 thorax and abdomen covered with stiff black hairs (Fig. 26). 



The eggs are about 1 mm. in length, white and cylindrical. They 

 are deposited in masses of three himdred to four hundred upon dead 

 and decaying flesh and upon wounds, sores, or within the nostrils or 

 other natural mucous openings of man and lower animals. Hatching 

 may occur in from one to twelve hours from the time the eggs are 

 deposited. 



The larvae are white, apodal, slender, and quite active. The head 

 and segments are provided with spines which facilitate their burrowing 

 into the living or putrefying flesh upon which they feed, a habit which 

 gives to the mature insect its common name of screw worm fly. Under 

 most favorable conditions the full larval growth is reached in three days, 

 at which time they may be half an inch or more in length. When mature 

 they leave the flesh upon which they have been feeding and bury them- 

 selves in the earth near by, in which location they enter upon pupation. 



The pupae are 6 to 9 mm. in length, somewhat barrel-shaped, and 

 dark brown in color. The pupal stage may last from six to twelve days. 



Occurrence and Effect. — The screw worm fly is widely distributed, 

 being found throughout North and South America. In the United 

 States it is especially abundant in the South, where it is responsible for 

 the most serious cases of human myasis occurring in this country. It 

 begins to attack in June, but has its greatest period of activity in the 



