“May 26, 1949: Found freshly dead and 
full of adult maggots along the trail from 
the Food Pen to the North Alley Burrow. 
The presence of adult maggots and the 
indications that the rat died last night, 
must mean that flies laid eggs on an ex- 
tensive wound area, and finally as the 
maggots matured and invaded more of the 
rat, they killed it. In the evening when 
food was placed in the Food Pen other rats 
running out of the Food Pen to the North 
Alley Burrow ran over it stepping on it”. 
“May 27, 1949: Remains of this rat found 
on Path 4. The bones were stripped of all 
fresh flesh by other rats, even though plenty 
of food was present in the Food Pen. 
(3) Male 677: “May 26, 1949: This rat died 
shortly after it entered the gathering sack 
from an entry to Area IV Burrow, which 
was being excavated. Flies presumably 
had laid eggs in wounds which must have 
been on the left cheek and right shoulders. 
Maggots have eaten all muscular, and other 
tissue about scapulae, humerus, entire throat 
region, left cheek, and thoracic vertebrae 
between the scapulae. Fur shows no sign 
of having been groomed in a long time.” 
Under the conditions in which this colony ex- 
isted maggot infestation was certainly one of the 
prime mortality factors. This is probably not 
generally true for rats living eleswhere unless the 
conditions are such as to foster social strife and the 
resultant fighting. Those rats which receive ex- 
tensive wounds and are thus more subject to screw 
fly attack are those larger, rapidly maturing rats 
who contend unsuccessfully for high-social rank. 
Several hundred rats were examined from city 
blocks in Baltimore where garbage occurred 
widely distributed in open containers. None of 
these rats was extensively wounded, and few had 
over two to three small nicks on their bodies. 
Wherever availability of food or haborage is limited 
it is likely that the competition will be increased 
and that during the warmer months infestation 
by screw fly maggots will be an important mortal- 
ity factor. In his discussion of screw fly infestation 
of livestock Bishop (79) makes no mention of rats 
or other wild animals serving as reservoir hosts. 
Warbles (Cuterebra) represented another avenue 
of dipteran contribution toward ill health among 
rat .. Sites of infestation included: body (8 rats), 
forelegs (2 rats), genital or anal region (12 rats), 
head (1 rat). The sites of infestation frequently 
became infected following the emergence of the 
larvae. Among males one or both testes might 
become free of the scrotum and eventually lost, 
or the penis become free of its sheath and point 
posteriorly. 
d. The relationship of sex to health and mortality. 
The prior comments and other aspects of ill health 
and mortality are summarized in table 64. These 
will be discussed row by row. Rows A and B 
refer mainly to wounds received in combat. In 
table 56 are additional data regarding wounds 
received in combat. Both sets of data give evidence 
of the grater frequency and severity of wounds 
received by males (also see remarks on pp. 95 to 
96). Most of the body injuries were open 
wounds, although a few were purulent sealed 
nodules. 
Row C, Tail Injuries: Included here are the 
following categories: (a) enlarged knob or swollen 
along whole length: male (1), female (4); (b) part 
of tail missing: male (6), female (2); (c) tail verte- 
brae rigid as if fused: male (3), female (2). 
Row D, Foot Injuries: The general picture of con- 
ditions here is that a foot (never more than one on 
the same animal) becomes swollen, small purulent 
areas develop on the surface, the swelling may or 
may not subside, toes may drop off, and the foot 
may become stiff as if the bones had fused. Seven 
of the nine males were 300 or more days of age 
before an infected foot was observed. 
Row F, Bronchiectasis: Rats which were found to 
be sneezing, coughing, wheezing or otherwise 
seemed to have difficulty in breathing were placed 
in this category. The age distribution was under 
200 days (14), 200-300 days (2), over 300 days (5). 
Although there is no direct evidence for this, it is 
probable that colds are a very important debili- 
tating factor contributing to the mortality of those 
individuals who for other reasons are not in good 
health. Four of the individuals having colds were 
also emaciated and weak. 
Row G, III Health — General: Grouped here are such 
varied items as emaciation, arthritis, fly eggs in 
fur, and difficulty in reviving after anesthetization. 
The four rats which were especially arthritic had 
their vertebral columns permanently arched, and 
they walked with an awkward lumbering gait. 
Rows H and I, External Parasites: Each rat 
handled was usually examined for external para- 
sites by blowing the pelage forward. Only one 
flea was observed. Four of the five ticks were the 
240 
