A CONSIDKHATIOX OF TIJE IXSFOT POFULATIOX AsROCTATKD 
WITH Cow DUXO AT (-RAAVEHY, W.A. 
241 
Fourth Stage, 
Except for occasional specimens, usually Staphylinicis, the population of 
adult beetles is low apart from Aphodius amhiguus. Larvae and pupae of 
Staphylinids, Cercyons, eggs and larvae of Aphodiines are present in the peri- 
pheral regions. The Psychodids have disappeared. Larvae of Sciara sp. 
hatch out in tliis stage. Most of the Brachycerous Dipteran larvae have 
pupated. Mites and Collembola still remain in some numbers. 
Fifth Stage. 
The population is essentially similar to that of the previous stage, progres- 
sively diminishing in size as the dung becomes drier. Ultimately, in the 
final stages, the Aphodiine larvae have undergone metamorphosis and vanished. 
The dung no longer contains insects and serves only to shelter a few, the 
presence of which under it is purely fortuitous. 
The following minor successions compose the main one : — 
1. The succession of visitors to inhabitants, which arises out of the 
alteration of the dmig, due more to oxidation and other chemical 
changes at its surface than to any activities of the insects. 
2. The succession among the adult Coleoptera. The majority of the 
early invaders move out in the third stage and are succeeded by 
Aphodius amhiguus in the early fourth, which is replaced in 
turn only by the casual shclterers of the fifth. The cause of 
the emigration in the third stage is not always clear. High 
population densities may cause a rapid change in the quality 
of the dung which becomes unsuitable for the adults and con- 
sequently they leave. There are, however, many instances 
in which the insects abandon the dung v’hile it still offers abund- 
ant food and space. Competition may cause the emigration of 
surplus individuals. This would lessen its intensity and there 
would be no reason for any more to leave. The exodus of 
all beetles from a dung of this type may be due to the tendencies 
found among gregarious insects to keep close together and to 
imitate each other’s movements, which are believed to be re- 
sponsible for such phenomena as the swarming of locusts (Uvarov, 
1928). It is an open question whether the gregariousness 
of dang beetles is real or due to purely chance associations 
resulting from largo numbers of individuals responding to the 
same stimulus. In any case, the migration of dung beetles is 
a gradual jorocess not comparable with any form of swarming. 
3. The succession among the larval stages. Larvae appear in cow 
dung in the following order : — 
1st Stage — Sepsid, Drosophilid, Borborid (?), Miiscid. 
2nd Stage — Psychodid. 
3rd Stage — Hydrophilid, Staphylinid. 
4th Stage — Aphodiine, Sciarid. 
In carrion the succession is assisted by the predaceous activities of the 
secondary blowfly maggots which actually attack or drive off those of the 
primaries. In the cow dung i)opulation none of the larvae of importance in the 
succession arc predatory on the others except those of Staphylinids, which do 
not appear in sufficient numbers to influence the total, Aphodiine larvae 
succeed those of Cercyon only because their physiology is better adapted to 
existence in fourth stage dung. The effect of competition is therefore to 
regulate the number of individuals found in any stage and plays little part 
in replacing one species by another. 
