606 Cura PING 
1916, larvae and pupae were found in almost every pool, because the adults 
started to breed early, while in 1917, in the first twenty days, only one or 
two were found. For such contrast the difference in temperature is 
considered the most probable cause. 
As far as the number in all stages is concerned, the summer of 1917 
outstripped the preceding year, in spite of the delay in appearance of 
the adults. After the adults had appeared, they soon started to breed. 
High humidity facilitated the hatching of the eggs and the development 
of the larval and pupal stages, thus bringing forth great numbers of 
adults. The immature stages were produced in corresponding abundance. 
There is every reason to believe that the great number of this species 
found in the summer of 1917 was due to the frequent rains that were so 
characteristic of that season in this locality. During the previous year 
the amount of rainfall was considerably less, and this species was corre- 
spondingly more scarce. 
COMMUNAL LIFE 
Being able to live in great fluctuation of density and salinity, Ephydra 
subopaca has a decided advantage over other insects in the salt pools. 
Here competition or the struggle for existence between this species and 
all others is by no means keen. Besides Hphydra subopaca, the per- 
manent members of the same community consist of five insects, four of 
which are coinhabitants, while the other is more or less an intruder 
and an enemy to the adult flies of the species. This latter is the common 
water strider, Gerris marginatus, mentioned in the preceding pages. 
This insect is, however, very rare. Among the other four the most abundant 
and common form is the larva of a mosquito, Aedes curriet Coq. This 
larva 1s numerous In some pools and sometimes it outnumbers the species 
of Ephydra, but it is not able to endure high salinity. Consequently, the 
larvae have never been found in pools D, E, I, and II, the salinity and 
density of which are high (page 365). 
Rat-tailed maggots are found in most of the pools. They are able to 
endure a salinity as high as that of pool D, and in this respect they can 
compete with the larvae of Ephydra; but the number is far inferior, 
and only now and then one or two are found, so there never could be very 
much competition for food and shelter between the two species. A few 
larvae of Culicoides and a great number of Chironomus are also found 
