446 Observations on Habits and Parasites of Common Flies 
occasion was as low as 23° F. During November when the larvae 
devoured great quantities of food the mean daily minimum temperature 
in this “tin” was 32-4° F., the mean maximum 44-1° F. 
As it was thought that the conditions in the “ tins ” might be 
abnormal the earth in an open air cage was examined. On Jan. 14, 
1916, an artichoke root was pulled up with some earth attached to it. 
18 blow-fly pupae and 19 larvae were found in this earth, showing 
that in regard to the presence of larval and pupal forms the conditions 
in the “ tins ” and in the earth were similar. 
In order to determine how far down into the earth larvae make 
their way before pupating, a small area of the earth in the cage to the 
depth of 6 inches was carefully dug up and examined. Slices an 
inch in depth commencing from the surface were studied. In the 
upper inch (27 cubic inches examined) 24 pupae and 9 larvae were 
found, in the second inch (18 cubic inches) 5 pupae and 5 larvae, and 
in the third inch (18 cubic inches) only 2 larvae. Below this no larvae or 
pupae were found. Both the pupae and larvae were lying in definite, 
smooth-walled moulds, each cavity being considerably larger than the 
pupa or larva. On being disturbed the larvae crawled rapidly. The 
thirty-five larvae and forty-seven pupae obtained from the earth in 
the cage were placed in muslin-covered jars and kept in a warm room 
in which the maximum temperature reached 52° F All the larvae 
soon turned into pupae and blow-flies (46 males and 33 females) 
emerged between Feb. 14-24. Of the remaining 3 pupae two were 
decomposing and one contained a braconid parasite. 
Also some of the larvae in “ Tin II ” were separated from the pupae 
on December 31, 1915, and kept in a jar in the tin. In this tin blow¬ 
flies began to emerge from the winter pupae on March 19, and from the 
jar containing the separated larvae on April 2. 
In the winter of 1914-15 very few larvae were noticed amongst 
the numerous pupae in the experimental “ tins” and cages. In that year 
the mean monthly temperature recorded by a thermometer exposed on 
the grass gradually declined in the autumn, being 38-3° F. in October, 
32-2° F. in November, and 30-0° F. in December, giving time for most of 
the larvae developing from eggs laid in September and October to 
pupate. In the autumn of 1915 on the contrary a prolonged period 
of cold weather occurred in November, the mean grass temperature 
dropping from 35-8° F. in October to 25-3° F. in November. This spell 
of cold weather probably checked the development of many of the 
late larvae. In the “tins” many of the larvae pupated under pieces 
