Oestridce, or Bot-flies 
113 
Gastrophilus equi is the most widespread and common of the horse 
bot-flies. Portschinsky reports it as commonly causing subcutan¬ 
eous myasis of man in Russia. 
Hypoderma bovis ( = Oestrus bovis), and Hypoderma lineata are 
the so-called warble-flies of cattle. The latter species is the more 
common in North America but Dr. C. G. Hewitt has recently shown 
that H. bovis also occurs. Though warbles are very common in 
cattle in this country, the adult flies are very rarely seen. They 
are about half an inch in length, very hairy, dark, and closely resemble 
common honey-bees. 
They deposit their eggs on the hairs of cattle and the animals in 
licking themselves take in the young larvae. These pass out through 
the walls of the oesophagus and migrate through the tissues of the 
animal, to finally settle down in the subcutaneous tissue of the back. 
The possibility of their entering directly through the skin, especially 
in case of infestation of man, is not absolutely precluded, although 
it is doubtful. 
For both species of Hypoderma there are numerous cases on 
record of their occurrence in man. Hamilton (1893) saw a boy, 
six years of age, who had been suffering for some months from the 
glands on one side of his neck being swollen and from a fetid ulcera¬ 
tion around the back teeth of the lower jaw of the same side. Three 
months’ treatment was of no avail and the end seemed near; one day 
a white object, which was seen to move, was observed in the ulcer 
at the root of the tongue, and on being extracted was recognized as a 
full grown larva of Hypoderma. It was of usual tawny color, about 
half an inch long when contracted, about one third that thickness, 
and quite lively. The case resulted fatally. The boy had been on a 
dairy farm the previous fall, where probably the egg (or larva) was 
in some way taken into his mouth, and the larva found between the 
base of the tongue and the jaw suitable tissue in which to develop. 
Topsent (1901) reports a case of “creeping myasis” caused by 
H. lineata in the skin of the neck and shoulders of a girl eight years 
of age. The larva travelled a distance of nearly six and a half inches. 
The little patient suffered excruciating pain in the place occupied by 
the larva. 
Hypoderma diana infests deer, and has been known to occur in 
man. 
Oestris ovis, the sheep bot-fly, or head maggot, is widely distrib¬ 
uted in all parts of the world. In mid-summer the flies deposit 
