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 Jan., 1919 PARASITISM OF NESTLING BIRDS BY FLY LARVAE 37 tact that it is difficult for the fly larvae to keep from falling out of loosely con- structed nests. All of the 1844 larvae in Table II, excepting the seventy-one indicated by the starred foot-note, were those of Protocalliphora azurea. These seventy-one lar- vae were taken from a linnet nest which contained the skeletons of three young which had been overtaken by death just before they became full-fledged. Death had undoubtedly been caused by the larvae. When the latter were discovered, hey were in their pupal stage and were considerably smaller than the larvae of Prolocalliphora azurea. All of them, excepting about a dozen, had hatched. These unhatched pupae were guarded very carefully, but they all proved to be parasitized by Nasonia brevicornia. The death of six other nestlings, including the four which had died in 1913, could be traced with more or less certainty to the Muscid larvac, as in the case of the three linnets whose skeletons I found, and the two goldfinches used for experimenting. One of these nestlings, a nearly full-fledged California Lin- net, was discovered when it had been dead only a short time. A number of the Protocalliphora larvae had actually penetrated into its body. The nest in which this dead bird was found contained another nestling of the same brood. Though apparently rather weak, this nestling took wing when I approached the nest. Nearly all of the fly larvae found in this nest showed traces of fresh blood. It was not until after I had completed my investigations that my attention was called to two articles concerning blood-sucking fly larvae . As far as I am able to ascertain, these are the only two instances of blood-sucking fly larvae on record as far as North America is concerned. In the second of these two articles Coutant mentions four papers (those by Dufour, Du Buysson, Rouband, and Rodhain) concerning blood-sucking fly larvae in Africa, South America, and Europe, but neither the Harvard University Library' nor the Boston Public Library contain any of these four articles. iu 1908 Henshaw (loc. cit.) recorded the infestation of two sdccessive broods of Bluebirds (Sialia sialis) by the larvae of Protocalliphora chrysorrhea (Mei- gen), which had been reported to him by Mrs. Emma F. Everett, of Wellesley Hills, Massachusetts. These two cases of parasitism were decidedly fatal, seven out of the eight nestlings dying as a result. Henshaw closes with a note of warn- ing about the danger of this insect pest to our native birds. Seven years later Coutant (loc. cit.), while studying blood parasites of the Common Crow (Corvus brachyrhynchos) at the Biological Laboratory of Cornell University, came across some larvae of Protocalliphora azurea. Most of his de- ductions, based upon the study of these larvae, are well founded. His conclu- sion however (loc. cit., p. 139) that "the larvae prefer rather dry places to moist ones and are therefore not accustomed to living in decomposing or fecal mate- rial" and that (loc. cit., p. 143) "the larvae when ready to transform, apparent- ly leave the more occupied parts of the nest in the vicinity of their food-supply and scek a dry portion" of the nest, were not borne out by my observa- tions and experiments. In all cases the larvae preferred the moist faecal material and pupated in it. This discrepancy between Mr. Coutant's results and mine is ndoubtedly due to the fact that Mr. Coutant based his conclusions upon the study of a comparatively few larvae, and that even these few were not studied by him in their natural environment, the bird's nest. a. Henshaw, H. W, A Parasitic Fly Injurious to our No. tive Birds. The Auk, xxv, 1908, pp. 8788. b. Coutant, Albert F. The Habits, Life History, and Structure of a Blood-sucking Muscid ko. rvae (Protocallilhoa Auea). Journal of Po.rsitology, vol. I, 1915, pp. 135-150.