604 ‘Coin PInG 
Not long afterward it came out again with the prey still in its possession. 
There may be more enemies among the insects, but no others were observed. 
The writer once found a water mite, Limnochares, attached to the cheek 
of an adult fly, as an external parasite. 
DISPERSAL 
Ephydra subopaca may be dispersed, perhaps for a long distance, 
during the pupal stage. As already mentioned, it is impossible for the 
adult to make a long journey on the wing. Since the larva, although able 
to crawl in soft mud, has no means of locomotion elsewhere after the 
moisture in the mud is all gone, there is no chance for it to travel from 
one place to another. As soon as the prepupal period is at hand, the 
perching habit enables the animal to secure stable foothold. Then there 
comes the possibility of migration, because wherever the supporting 
object is shifted, the pupa will go with it. Dispersal is facilitated by 
three characteristics of the pupal stage— one held in common by ail 
insects, and two particularly pertaining to this species: first, during the 
pupal stage, the animal does not require food; second, the pupa always 
has a very firm hold on its support, so that there is no danger of its being 
shaken off; third, the thick and hard puparium enables the animal to 
stay outside of water for some time, and also serves, as already mentioned, 
for protection from injury during its journey. 
Many times the writer, in lifting a fragment of wood from the pools, 
found hundreds of pupae, both mature and young, scatterd along the edges 
of the stick. These could never be removed by shaking or jerking. Several § 
times an enormous number of pupae were found firmly attached to a piece § 
of cord which had been thrown into a shallow pool. Whether in water 
or in the soft mud area, or exposed to the air, these pupae are able to 
attain maturity if no extremely unfavorable conditions occur. Attached 
to such supports, they may be brought from one place to another by 
train or other carrier, and thus dispersal of the pupae may be accomplished. 
Aldrich (1912) lists the localities where this species has been found 
as follows: Massachusetts, Woods Hole (Melander); Connecticut (Loew) ; 
New York, Ithaca, at salt pools (Johannsen); New Jersey, several locali- 
ties (Smith catalog); Illinois, Gallatin County, at salt pools (Packard); 
Utah, Box Elder Lake, in salt water, Garfield in brackish seepage, Promon- 
tary Point in brackish spring; Idaho, Market Lake, m overflow from 
