MYIASIS— TYPES OF INJURY, LIFE HISTORY, HABITS 191 



The life history of the common bot fly is about as follows : The eggs 

 are attached to the hairs of the host, mainly on the legs, but frequently 

 on other parts. These are ready to hatch in from nine to forty days. 

 The larvse are removed from the eggs by the biting and licking of the 

 host. They take up their abode in the stomach, remaining attached to the 

 mucous coatings of the pyloric end of this organ until fully grown sev- 

 eral months later. They then detach and pass out with the manure, 

 pupate near the surface of the ground and produce the so-called bot flies 

 three to six weeks later. The cycle is completed in about a year. The 

 life histories of the nose fly and throat bot are similar but differ especially 

 in the method of oviposition. The former deposits its eggs, which are 

 nearly black, on the very minute hairs around the lips. The young larvae 

 gain access to the mouth and develop as in the common bot fly, but before 

 passing out they usually catch hold of the mucous membrane of the 

 rectum and are often seen protruding from the anus a few days before 

 dropping. The annoyance produced by the oviposition of this fly is 

 very severe. The throat bot deposits its eggs mainly under the jaws and 

 the larvffi are often found in the duodenum and also attach in the stomach. 



In addition to the annoyance produced at the time eggs are deposited, 

 heavy infestations in the stomach interfere with digestion and cases are 

 recorded where the larvae caused death by stopping the pyloric opening. 

 The irritation of bots, which may be present in numbers exceeding 1,000, 

 must be detrimental to the host. The throat bot also attaches in the 

 pharynx in its early stages and is accredited with causing the death of 

 animals from this habit. 



Cases of dermal myiasis in man attributable to these species have 

 already been mentioned. European writers have also reported the occur- 

 rence of larvae of Gastrophilus in the eye of man. 



Passing to those forms which are more or less accidental, the Sar- 

 cophagidae demand first attention. Hasseman has reported a case in 

 which an entire family was infested with the larvae of Sarcophaga Jiaemor- 

 rhoidalis, the maggots being passed in considerable numbers during warm 

 weather. Numerous other similar instances have occurred and in prac- 

 tically every instance they are traceable to leaving foods exposed to flies 

 between meals. Since the Sarcophagids deposit living larvae on meats, 

 etc., th^y may be easily overlooked. 



Cases of intestinal myiasis due to Eristalis larvae are common in this 

 country. A good summary of these cases has been made by Hall & Muir. 

 It appears that they sometimes give rise to acute colicky pains but no 

 serious symptoms. As is well known, the rat-tail larvae are to be found 

 in decaying vegetation and in water, and the source of infestation must 

 be through the swallowing of uncooked and poorly cleaned food such as 

 watercress and lettuce, and the drinking of unclean water. The follow- 



