FLIES AS TRANSMITTERS OF WORM PARASITES. 
localities. The percentage infection of house flies captured in stables 
by us was 7.6. Under experimental conditions, using horsedung known . 
to be infected, 82 per cent. of the emerging flies harbored Habronemu, 
the number of parasites in each infected fly varying from 1 to 41. In 
addition to these Eidsvold records, we found that 27 out of 66 M. domes- 
tica bred from horsedung from a livery stable in Brisbane were infected 
(i.e., 41 per cent.)—23 with H. muscw alone, 3 with H. megastoma 
only, and 1 with both species. 
The low percentage (2.2) of infection amongst captured M. fergusoni 
was almost certainly due mainly to the fact that this fly prefers cow- 
dung to horsedung for larviposition, hence few larve were likely to 
become infected with Habronema. On the other hand, when the species 
was bred from horse manure, it became readily infected (95 per cent.). 
The number of worms found in parasitized captured flies ranged from 1 
to 18, with an average of 4; whereas in bred infected insects the number 
varied from 18 to 91, being frequently between 40 and 70. As already 
stated, this species breeds normally in cowdung in preference to horse- 
dung; so also does M. vetustissima, which gave similar results in regard 
to infection, being 5 per cent. in captured flies, and 100 per cent. in 
bred flies. In the latter case, infestation was often extremely heavy, in 
one batch of 22 the numbers ranging from 39 to 97, with an average of 
71 worms, both species being represented. In regard to M. terrwregine 
and M. hilli, both were very scarce in the district, but when bred out 
from infected horsedung in Hidsvold and Brisbane respectively, both 
became readily infected with both parasites. ; 
It was found that flies of various species, when heavily infested 
experimentally, died off rapidly, being sickly during captivity. No 
doubt a similar circumstance occurs under natural conditions, so that, 
in all probability, it is only when flies are bred in lightly infected 
material that they are able to survive for any length of time as infected 
insects. This is probably a partial explanation of the low percentage of 
parasitized captured flies. One must not overlook the possibility of the 
larvee originally present having all escaped from an infected fly before 
‘the latter was captured. : 
It was observed that native species of Musca became much more 
heavily infested with Habronema than the house fly did when placed 
under similar conditions. This remark applied to both M. vetustissima 
and M. fergusoni, the only two tested for the purpose. Eggs of the 
house fly and M. vetustissima, laid on the same day, were placed to- 
gether in a jar containing horsedung known to be infected with Habro- 
nema, fresh material being added when necessary, always from the 
same source. M. vetustissima emerged some days before M. domestica, 
owing to its shorter larval periods, and on examination all (22) were 
found to be parasitized, the number of. worms counted ranging from 39 
to 97, with an average of 71. In the case of the house fly, 46 were 
collected, 36 («.e., 78 per cent.) being infected, the parasites ranging in 
number from 1 to 20, with an average of 4.4. 
Habronema microstoma. 
Both Hill and Bull have already shown that the stable fly (Stomoxys 
calcitrans) is apparently the normal transmitter of Habronema micro- 
stoma, and does not become parasitized by either of the other species. 
371 
