182 SANITARY ENTOMOLOGY 



SUBDERMAL MIGRATOKY SPECIES 



The species concerned in this form of myiasis are truly parasitic. 

 In the cases of man they can not be considered as especially dangerous, 

 but in animals they assume first rank as destructive parasites. 



The type of myiasis produced by these larva; is described under 

 various names in medical literature but especially mentioned as creeping 

 disease. This is owing to the movement of the larva; in the subcutaneous 

 tissues. In the United States we have little concern for cases of myiasis 

 in man produced by this group of flies as they are comparatively infre- 

 quent. The species concerned are Hypoderma, probably mostly lineata 

 DeVillers and Gastropliilus, probably mostly mtestinalis DeGeer (plates 

 X, XII). Unfortunately the larvffi concerned usually have not been 

 preserved, and in a very few cases have any larvae from man been reared 

 to maturity'. 



The sanitary entomologist is not particularly concerned with the 

 Oestrids infesting cattle, but on account of their importance to the 

 veterinary entomologist they are here briefly discussed (see plates XI, 

 XIII). There are two species in this country, H. lineata De Villers and 

 H. hovis DeGeer. The former is the predominant form in the United 

 States, especially in the southern three-fourths of the country, while the 

 latter is more restricted to the northern tier of States, New England and 

 Canada. The adults are known as heel flies and oviposit on the hairs, prin- 

 cipally on the legs of cattle. These eggs hatch in three or four days and 

 the larvffi penetrate the skin at the point of attachment or in some 

 instances may be taken in by licking. After several months spent in the 

 body of the animal they appear during the late fall and winter months 

 under the hide along the back, forming subcutaneous tumors. When full 

 grown these grubs emerge from the host, drop to the ground and after 

 about twenty-five to thirty-five days spent in the pupal stage produce 

 flies which are ready to attack cattle the first warm days during spring. 



Several cases have recently come under the observation of Mr. E. W. 

 Laake and the writer of the occurrence of this species in the backs of 

 horses. These are responsible for the production of lesions which prac- 

 tically render the use of the infested animals as saddle horses impossible 

 for a few weeks. 



There are a number of records of the occurrence of the young larvae 

 of these flies in man, especially children. Attention is usually first called 

 to them on account of pain, soreness or itching in the region of the 

 shoulders or face. The irritation is sometimes rather acute and its 

 location moves with the burrowing of the larvas. Before becoming mature 

 the grubs appear near the surface under the skin or beneath the mucous 

 membranes of the mouth and can there be extracted with ease. 



