Jan., 1919 PARASITISM OF NESTLING BIRDS BY FLY LARVAE 35 
eral others which were being prepared for dissection were placed in a fixing fluid 
for six hours, then washed in a 50 percent alcohol solution and placed in one of 
80 percent. They were still alive two days later and it was necessary to resort 
to a stronger fixing fluid (Gilson’s) to prepare them for dissection. Other lar- 
vae were placed in a very strong insect powder, but they remained alive in it for 
two or three days. 
As soon as the larvae pupated, the pupae were placed beneath inverted 
tumblers. After the flies emerged from the pupae they were kept in a large, 
narrow-mesh cage and carefully studied. It may be of interest to state that the 
flies (about 1500), practically without exception, emerged from the pupae be- 
tween seven o’clock in the morning and two o’clock in the afternoon. Upon 
emerging they were of a slightly lighter hue than the adult of our Common 
House-fly (Musca domestica), their wings being shriveled up, but after about an 
hour or so these straightened out and the young flies assumed the dark blue, me- 
tallic lustre of adult Protocalliphora azurea. 
Various kinds of food were placed before these flies, such as milk, crushed 
fruit, cheese, and meat in various forms. The flies readily ate the milk and 
fruit, especially if the latter was placed on the cage wire instead of the cage 
floor, but they were rather indifferent to the meat and the cheese. Although 
some of the flies were kept in the cage for six or seven weeks, none of them, to 
my knowledge, deposited eggs or maggots. 
One day I noticed a number of very small, bee-like insects, since identified 
as Nasonia brevicorms by Professor Brues of Harvard University, flitting about 
in one of the inverted tumblers. I wondered where they had come from, but 
thinking that they had perhaps got into the tumbler accidentally, I let them es- 
cape. To my surprise I found some twenty or thirty more of them under the 
same tumbler the following day. Upon investigation, I found one or two small 
holes of about the size made by an ordinary stick-pin in several ‘of the pupae. I 
could easily tell by the weight of the latter that they were empty. This gave me 
a clue. I opened a number of the pupae and there found these little insects, more 
commonly known as Chalcid Flies, in several stages of development: as white, in- 
active maggots; as creamy, pink-eyed larvae, already showing their insect form; 
and as full-grown insects which came swarming out as soon as the fly pupae were 
opened. I counted the Chalcid Fly larvae from a dozen pupae and found them 
to vary in number from about fifteen to twenty-five per Muscid pupa. In all 
these cases the embryo fly had been completely devoured. 
Some forty or fifty of these Chalcid Flies were then transferred to an in- 
verted aquarium jar below which a hundred Muscid pupae were placed. The 
Chaleid Flies seemed to be perfectly at home among these pupae, crawling about 
among them as do bumble-bees among their honey-combs. Within a few weeks 
bundreds upon hundreds of young Chalcid Flies emerged from the Muscid pu- 
pae; less than a dozen Protocalliphora hatched, the remaining ones having been 
parasitized by the Nasonia. 
In some of the infested birds’ nests, I had noticed a number of small grubs, 
similar in size and form to those found in almonds. As in the case of the Chal- 
cid Flies and the larvae of the Protocalliphora, I paid no attention to them at the 
beginning, but when they occurred repeatedly, I began to suspect that they 
might have some relation to one or both of the other insects. I therefore col- 
lected some fifty or sixty of these grubs and placed them among a large number 
of Muscid pupae, many of which were parasitized by Chalcid Fhles, and watched 
