1919] Plath: Bloodsucking Fly Larvae in Birds' Nests 193 



As I had found it rather difficult to observe nestlings of wild birds 

 closely in the open, I decided to use a brood of tame canaries for 

 further experiments. I succeeded in securing a female bird with two 

 nestlings about a week old. but both young died within a few days, 

 probably because they had taken cold while being transferred to ray 

 room. For these I substituted four, nearly full fledged, green-backed 

 goldfinches (Astragal in us psaltria hesperophilus Oberholser). 



A few days later forty of the most active larvae were selected from 

 some two hundred. None contained any fresh blood and many of them 

 were only half grown. These forty larvae were placed on the young 

 birds in the early part of the afternoon and developments observed 

 from time to time until about 8:30 p.m. At first the nestlings showed 

 some uneasiness by shaking themselves, but this only lasted for a 

 minute or two, after which they again came to complete rest. There 

 was nothing further unusual in their behavior during the next six 

 or seven hours. 



At 3 a.m. the next morning one of the nestlings was found at the 

 bottom of the cage and the others, including the mother bird, were 

 sitting on the rim of the nest and not huddled closely together in the 

 center. Two of the fly larvae were crawling about at the bottom of 

 the cage and had evidently been dragged down by the nestling, 

 because it would have been impossible for them to get out of the 

 nest-box in any other way. They were only half grown and were 

 gorged with fresh blood. Thereupon the four remaining birds were 

 carefully examined. About four or five of the larvae were clinging 

 to the feet and lower parts of the body of each one of the nestlings. 

 None were found on the mother bird. Most of the larvae released 

 their hold while the birds were being examined, but some of them 

 had to be forcibly detached. These, like those found at the bottom 

 of the cage, were not full grown and were filled with fresh blood. No 

 marks, visible to the naked eye, could be seen where the larvae had 

 pierced the skin of the birds, nor were any traces of blood noticeable 

 on the nestlings. The four nestlings were then transferred to another 

 nest and their own carefully examined. From the latter sixty-eight 

 larvae were taken, showing that it had contained twenty-eight before 

 the forty were added. More than half of the sixty-eight larvae showed 

 fresh traces of blood, the smaller ones being most gorged. The soft 

 cotton lining of the nest-box was then removed and examined, but no 

 additional larvae were found. Thereupon the box was refilled with 

 cotton and the nestlings put back. The latter now appeared completely 



