220 
G. J. Snowball. 
In an imstable environment of a restricted nature, of which cow dung 
is an example, two main factors operate to influence the type of population 
present at any particular time. Firstly, the external climatic conditions 
change the nature of the environment, thus making it less suitable for the 
species which occupies it first. Secondly, the animals themselves, principally 
by interspecific competition, to a lesser extent by altering the physical and 
chemical nature of their environment, tend to bring about an alteration in 
the type of population. Ultimately a stage is reached at which a primary 
species is displaced by one more adapted to the changed conditions. The 
process continues until the environment is destroyed. This termination of 
the succession by destruction of the environment, which is characteristic of 
the animal ecology, serves to balance, in the broad cycle of energy of nature, 
the synthetic tendencies of plant successions in which a stable association is 
finally attained (Chapman, 1931). 
The phenomenon of succession has received most attention from plant 
ecologists. The most clear cut examples of succession in animal ecology are 
found in certain restricted environments. The work of Graham (1925) on 
the succession of animals in a felled tree trunk may be cited here. He con- 
cluded that there was a definite succession of organisms as the chemical and 
physical characters of the wood changed during the process of decay and dis- 
integration. Fuller (1934) found this statement to be equally true of the 
population of a carcass. 
In the case of cow dung, the succession is not clear cut and only detailed 
study would reveal the causes of some apparent anomalies. The nature of 
the succession will be discussed after the insects concerned have been dealt 
with. 
4. THE CHANGES IN COW DUNG AFTER DROPPING. 
The initial nature of a cow dung varies considerably with the diet of the 
animal. The dung of a grass-fed cow differs from that of one fed on dried 
feed in its green colour, soft texture, and the subsequent course of its dis- 
integration. The process of decay can be arbitrarily divided into five stages, 
of which the first three differ markedly from the last two. A characteristic 
insect population occupies the first three stages and a different one succeeds it 
in the last two. Certain distinctions can in many cases be dravn between the 
populations of Stages 1, 2, and 3, but equally often they are almost identical. 
Following is the typical course of changes in dvmg from a grass-fed cow : — ■ 
Stage. 
When dropped, the dung is green or more rarely tan in colour, semiliquid, 
and with a noticeable odour. Cow dung is characteristically a cold ” dvmg 
and liigh temperatures due to fermentation are unusual, especially in isolated 
cakes, although the temperature of the dung during the day may be high 
owing to exposure to the sun (Davidson, 1937). The slight degree of fer- 
mentation undoubtedly influences the insect population since certain insects, 
e.g., tlie house fly, are specifically attracted to fermentable materials either 
by high temperatures or products of such decomposition. 
The first obvious change in the cow dung is the formation of a thin 
blackish skin over the exposed surface of the soft mass. By evaporation 
of moisture, this skin ultimately becomes a thick, firm crust pierced by many 
cracks which expose the softer interior. The superficial skin is the result of 
an oxidation process dependent on free access of atmospheric oxygen, since 
it does not form on artificially covered cakes or those which for any reason 
are kept exceedingly moist. 
