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 Jan., 1919 PARASITISM O1; NESTLING BIRDS BY FLY LARVAE 31 The pale mouths and ultimate death of the nestlings were no longer a mys- tery. They had been gradually bled to death by the maggots. I regretted the unhappy fate of the young songsters and avenged them as best I could by killing the maggots, thinking that this form of parasitism was no doubt generally known to zo51ogists. The surviving nestling soon recuperated and later became a great pet of the family. Intermingled with the lower part of this infested nest there was a mass of a sticky, dark brown substance reminding one of clotted blood. Evidently this material either was the faeces of the maggots or coagulated blood which had trickled from the wounds made by the maggots, but as I could find no trace of wounds on the birds, I concluded it to be the former. About two weeks later I found the nest of a Willow Goldfinch containing four young ones, some of which showed the same symptoms as the Green-backed Goldfinches which had died. Suspecting that this nest also might be infested by maggots, I transferred the four nestlings to another nest and closely exam- ined their own nest. I found the same state of affairs as in the previous infested nest, with the exception that some of the maggots had already pupated. These pupae were of a light brown color and somewhat smaller than the maggots, being about 1.0 cm. in length and 0.5 cm. in width. Both maggots and pupae were de- stroyed as in the first case. The swelling of the eyelids soon disappeared and I had no difficulty in rearing this brood of goldfinches; but one of the young birds turned o{t to be entirely blind so that it had to be killed. Two others were blind in one eye, whereas the fourth was normal. Two of these birds lived in cap- tivity for several years. Later in the summer I met Dr. C. A. Kofoid, head of the ZoSlogical Depart- ment of the University of California, and told him about the maggots and the pupae. He regretted that I had destroyed them and suggested that I look into this matter more closely the followng summer. It was impossible for me to do this, however, until the summer of 1917. The period of investigation which I am now about to discuss, extended from the latter part of June, 1917, unti about the middle of September. The work was carried out under the supervision of Professor W. W. Cort, of the Department of Zoology of the University of California, to whom I am indebted for a number of important suggestions. My first task was to see whether or not I could find any maggots. Since both infested nests had been those of goldfinches, I tried to locate as many of these nests as possible. Incidentally I also kept an eye on nests of other birds which I chanted to run across. My efforts were quickly rewarded. The first nest examined, that of a Nuttall Sparrow (Zonotrichia leucophrys nuttalli), con- tained thirty-six full-grown maggots like those encountered in the summer of 1913, and thereafter I found them in about two out of every three nests. To my surprise none of the young birds from these infested nests showed any eye trouble; nor did they, in the first few instances, seem to have fared any the worse in other respects from the presence of the maggots. Equally surpris- ing was the fact that no red appeared in any of the maggots taken from the first few nests, but merely the dark brown substance in the posterior part of the in- testine. Ninety of the most vigorous maggots, selected from 154 full-grown indi- viduals taken from the nest of a California Linnet, whose five full-fledged young showed no noticeable pernicious effects from this large number of creeping ver- min, were placed in a Green-backed Goldfinch nest containing three ymmg which were about four or five days old, and developments observed from day to day.