KILOGRAMS POPULATION 
1947 1948 1949,. 
Figure 146. — Growth of the population in biomass and 
number of individuals. 
thus it might be assumed that hunger was a factor. 
At this time, however, there were two other rats 
lying on the ground that had died from unknown 
causes. These two rats were not eaten by other 
rats until several days after the previously men- 
tioned overt incident of cannibalism. During the 
early months of this study, dead rats were ignored 
by their surviving companions, and left to be 
decomposed by bacterial and maggot action. 
This led to doubt concerning those statements 
which attributed a role to the act of cannibalism 
in the transmission of disease. Accompanying 
the increase in population density, however, there 
was an increase in social tension and in the fre- 
quency of cannibalism. Ten rats whose identity 
was known were eaten by other rats. Usually the 
dead rats were dragged into harborage boxes or 
burrows, the skin turned wrong side out and the 
flesh stripped from the bones. Other similar acts 
of cannibalism must have been overlooked, since 
burrows were rarely excavated by the investigator. 
Dead rats, which were partially decomposed by 
bacteria or maggots, were sometimes eaten by 
their companions. 
c. The relationship of flies to health and mortality. 
Fly larvae occasionally contributed to both mor- 
bidity and mortality. Unfortunately identification 
was not made of the species involved. Warbles 
most likely were of the genus Cuterebra. Larvae 
of the genus Chrysomya were identified from carcasses. 
This genus is known to be involved in cases of 
accidental myiasis in man and domestic animals. 
However, it was not known whether it was involved 
in the observed cases of myiasis of rats. Callitroga 
americana, the common screworm of domestic 
animals, is involved in myiasis of a semiobligate 
type but other genera have been observed in acci- 
dental myiasis. The following are the relationships 
of flies to rats in the colony: 
Rats removed from traps occasionally had masses 
of fly eggs deposited in their fur. These were 
usually the soft pelaged juvenile rats, although 
rarely adults were involved. The eggs were always 
combed from the fur before release. That flies lay 
eggs on free-ranging juveniles is evinced by the 
following field observation: 
“6-19-48: A young rat was seen to be wander- 
ing about the open pen. It entered harborage 
Box 21 which was then opened and the rat caught. 
It was a male about 34 days old that had not pre- 
viously been captured. Fly eggs were scattered 
through its fur. It was rather weak.” This rat 
was never caught again. 
The most significant effect of screw flies upon rats 
is when they lay their eggs in the extensive purulent 
wounds exhibited by some of the males. During 
fights males may receive a single gash or several 
smaller nicks in a single location. These frequently 
become infected and developed into extensive 
shallow festering wounds which may last for weeks 
or even months before healing. The lumbar 
sacral region is the most common site for these in- 
fections, usually just above the base of the tail, 
although occasionally they occur on the shoulders. 
During the colder months the flies are not a factor, 
but with the advent of warm weather open wounds 
predispose the rats to death by myiasis. The follow- 
ing three field notes describe the maggot-rat 
relationship: 
(1) Male 99“April 13, 1949: Two large infected 
wounds; one above base of tail (20 x 20 mm.), 
the other extends from left hip around anus. 
These are all wounds that have not healed”. 
May 28, 1949: “I noticed large green flies 
buzzing about the top of harborage Box 29, 
which was lying on the ground. On turning 
it over I found a rat that was a walking mass 
of maggots. He ran actively under a nearby 
board and finally escaped into tile 4 burrow.” 
“May 29, 1949: Rat in Passage 4 burrow 
tail protruding out, and green flies buzzing 
about. I tried to catch it by the tail but it 
ran further down the burrow.” 
This rat was not found in this burrow on June 1, 
1949, or elsewhere in the pen the following and 
terminal week of this study. If a rat is not found 
within a day or two after death by myiasis only the 
bones and a few patches of skin may be left solely 
as a result of the maggots’ consumption of tissues. 
(2) Male 69 “February 15, 1949: 22 body 
nicks”. It was not recorded again until: 
239 
