A COXSIDEKATIOX OF THE INSECT POPULATION ASSOCIATED 
WITH Cow Dung at Crawley^ W.A. 
221 
2nd Stage. 
The colour changes from tan or green to a light brown shade. The whole 
cake becomes firmer as a result of evaporation of moisture. The odour is 
still noticeable even when the surface remains unbroken. 
3rd Stage. 
The dung becomes blacker and firmer in texture. The fibres of the* 
undigested food can be distinguished, because evaporation of moisture has 
concentrated the suspension of which they form the discontinuous phase. 
The odour is usually not noticeable unless the surface of the dung is disturbed. 
4:th Stage. 
Evaporation of moisture has proceeded to the extent that undigested 
food fibres interlock to form a matrix firm enough for the whole cake to be 
held by the edge without breaking. The internal colour is a dull rusty brown. 
The surface layers of the dung are completely dry and of a bleached brown 
or even white colour due to the precipitation of salts. 
^th Stage. 
The entire dung becomes of the same nature as the upper portions of a 
fourth stage dung. It is firm, bleached brown, in some cases almost white,, 
dry, hard, and noticeably light for its volume. In the later part of this stage 
no insects except casual shelterers are present. 
A number of variations from the above cycle are possible. All parts 
of a dung cake do not necessarily pass through the same stage at the same 
time. For instance, dungs which have the upper layers in the fourth, and 
lower portions in the second or third stage, are common. Further, the changes' 
in colour, texture, and moisture do not always proceed at the same rate.- 
Dungs sometimes preserve the initial green colour although in other respects- 
they could be classed as in the fourth stage. Such peculiarities are due to- 
some unusual feature in the history of the cake, such as freedom from invasion, 
by insects or conditions which artificially preserve the moisture content. 
An important departure from the cycle outlined above is the omission, 
of either the second or the third stage. The colour of a dung may pass straight 
from green to black, i.e., direct from first to third, or from light brown to dark 
brown, i.e., from second to fourth. In such cases, the population of the- 
omitted stage is found in the early part of the third or late jmrt of the second 
according to whether the second or third has been rt'duced. 
In the field, large numbers of dungs disintegrate before they reach the 
fifth stage, an occurrence very frec|uent during tlie height of the summer.. 
The time taken to pass through the \-arious stages of decomposition* 
varies greatly with climatic conditions, so that, exceiit witliin wide limits,, 
the absolute age of the dung has little significance. High temperatures' 
speed up the process of disintegration by accelerating the cliemical and physi- 
cal processes within the dung and by stimulating the contained insects. Rain 
has the reverse effect, and the stages of a dung ex 2 iosed to rain may be indefin- 
itely prolonged. 
