16 MISC. PUBLICATION 6 31, U. S. DEPT. OF AGRICULTURE 



A discussion of the symptomatology and general pathogenesis of 

 enteric myiasis is given under the species involved, particularly 

 Fannia, Sarcophaga haemorrhoidalis, and Muscina stabulans. The 

 following symptoms seem to be fairly characteristic, according to 

 published case records. The patient suffers from general malaise and 

 weakness; his face is pale, and he has a complete loss of appetite. 

 Nausea and vomiting occur at the onset ; sometimes larvae are expelled 

 with the vomitus. Severe gastric pains may be present and may be 

 accompanied by bloating and tremulous motions in the area of the 

 stomach and upper intestine ; there may also be dizziness and violent 

 headaches. Sometimes, particularly in children, violent spasms and 

 epileptic fits may occur. The symptoms are those of an acute gastritis 

 or enteritis; they have been described as those of cholera morbis. 

 They disappear with the passing of the larvae. 



Infestation probably comes through the food, though sometimes 

 possibly through the drinking water, from soiled hands, direct deposi- 

 tion in the mouth, or other means. Larvae may be passed with the 

 feces, sometime in enormous numbers, or may be expelled in vomitus. 

 Many cases have been described in the literature. A particularly 

 obstinate one, involving unnamed species of three genera, is described 

 by Herms and Gilbert (57) ; others are cited at various places in the 

 text. 



ATTACKS BY BLOODSUCKING MAGGOTS 



Though not myiasis in the strict sense, bloodsucking by certain mag- 

 gots is mentioned as a related phenomenon. Several species of mus- 

 coid flies belonging to unrelated groups of genera parasitize nestling 

 birds in this manner, but only one species, the calliphorid Auchmero- 

 myia Juteola, attacks man and, unlike all the true myiasis producers, 

 is apparently specific to man. 



LIFE HISTORIES 



Though life histories of Diptera vary considerably, they conform 

 more or less to a given pattern. All flies have complete metamor- 

 phosis. The female usually produces eggs, though larvae in all stages 

 of development and, indeed, pupae are sometimes produced. The 

 larvae feed on a wide variety of substances ; they may be plant feed- 

 ers, scavengers, predators, parasites, or bloodsuckers. Some live in 

 water, some in a semiaquatic medium, some on land, some in decom- 

 posing plant or animal tissues, and some internally or externally on 

 the body of a host. The larval stage is the one actively involved in 

 myiasis. As a rule the larva passes through three developmental 

 stages, or instars, though variations from this number may occur. In 

 most Diptera the various larval instars of a given species bear a 

 general resemblance to one another. Conditions of pupation vary 

 with the species. The pupa in the higher flies is capsulelike in appear- 

 ance; in the lower flies the form varies considerably. Some species 

 may complete a generation within 2 weeks or less, while others require 

 a year or more. In temperate regions hibernation may take place in 

 any stage of the life cycle, but the stage that hibernates seems to be 

 rather definite for any given species. 



