40 MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



seems, with few exceptions, to be attracted only to the young of the 

 species, whether human or animal. The usual areas of infestation are 

 the neck, chest, shoulders, and arms, although sometimes the eyelids, 

 cheeks, palms, and navel are attacked. 



Even an attempted, unsuccessful penetration by the larvae may 

 cause noticeable irritation of the skin. When the larva has become 

 established, small, abscesslike lesions, each measuring 6-20 mm. in 

 diameter, appear. Closer examination will reveal, however, that the 

 apparent pus is in reality the posterior end of the larva, which is 

 constantly being extruded and withdrawn during the feeding opera- 

 tions. The lesions are suggestive of impetigo, and some cases have 

 been incorrectly diagnosed as that malady. In most cases studied by 

 Walker and Ford in Canada, 12 to 14 lessions were present, although 

 the number may reach as high as 40. Usually each larva penetrates 

 the skin independently, although as many as 5 larvae have been taken 

 from a single lesion. 



This disease may be diagnosed by the charateristic lesions, a slight 

 elevation in temperature, irritability, dehydration, and loss of ap- 

 petite. Secondary bacterial infection may occur. No fatal cases are 

 known to have occurred in man, though such are frequent in young 

 mink on fur farms. 



Since the lesions are usually open, the larvae may be removed with- 

 out an incision by gently applying pressure; antiseptic precautions 

 should, of course, be employed. Prevention consists in not permitting 

 small children to sleep out of doors in infested areas during the sum- 

 mer months. Screening may not always afford adequate protection, 

 since larvae may be dropped through screens or deposited where they 

 may be able to crawl into the screened area. Cleanliness is no safe- 

 guard against infestation, since these flies, unlike most members of 

 this and related families, are not attracted by fetid odors. 



Status as a Parasite. — In spite of the statement of Patton and the 

 earlier opinions of Walker to the contrary, this is probably a specific 

 myiasis producer. Patton's contention that the parasitic habit was 

 abnormal to this species was based on the small size of the spines of 

 the larval skin, these being usually better developed in parasites than 

 in saprophytes. However, Walker (157) seems to have reversed his 

 early opinion on the grounds that the habit of penetrating healthy 

 skin is not normal for a carrion feeder; the larvae have never been 

 recorded from carrion, except in laboratory experiments ; and gravid 

 females, according to laboratory experiments, are attracted, not to 

 carrion, but to living young animals, and will not larviposit on carrion 

 except as a very last resort. 



In addition to man, the young of domestic and wild animals, es- 

 pecially mink, are parasitized. 



Literature. — For immature stages, Walker (158) ; for habits, Ford 

 (40) ; for pathogenesis, Walker (157) and Ford (40) ; and for a 

 detailed account of parasitism in man and animals, Kingscote (69). 



WOHLFAHRTIA OPACA (Coquillett) 



Synonyms. — Paraphyto opaca Coquillett; Wohlfahrtia meigeni of American 

 authors, not of Schiner. 



Recognition Characters. — Adult : The second antennal segment is orange in 

 color and subequal to the third in length ; the palpi are likewise orange. There 

 are no presutural acrosticals. The abdomen is colored as in W. magnified, except 



