EASTERN HOUSE WREN 135 



Nests of the house wren have been found by Mason (1936) to be 

 infested by the larvae of the blood-sucking fly Protocalliphora splen- 

 dida sialia. These larvae have been found to be very destructive to the 

 young of such box-nesting species as the bluebird and tree swallow. 

 The nests of the wren are less favorable for the parasites, but even so 

 they have proved to be an important factor in the mortality of nestling 

 wrens. This has been found to be especially serious when the infesta- 

 tions are accompanied by other unfavorable conditions such as bad 

 weather, and lack of food which tend to lower the resistance of the 

 young. These flies are not known to be carriers of diseases, but, when 

 present in sufficient numbers in a bird's nest the larvae often suck 

 enough blood from the young birds to bring about their death. 



In the examination of 39 nests of the wren a total of 201 larvae and 

 puparia were found. A secondary parasite, which serves as a natural 

 check on ProtocalU'phora^ is the chalcid Mormoniella^ and it is thus 

 desirable to give this little fly every opportunity to increase in numbers. 

 When heavy infestations of the blood-sucking fly Protocdlli'phora 

 occur, it is important to clear the nesting boxes after the young are four 

 or five days old. 



It is well within the range of possibility that pests such as Proto- 

 calliphora have been an important factor in the local disappearance of 

 the wren in sections of New England where the English sparrow has 

 shouldered most of the blame. 



Spiders hatched from egg sacs carried into the nests with sticks 

 sometimes prove a menace to the wrens. Hathaway (1911) gives an 

 account of a pair of wrens that were driven away by spiders. His 

 story in part is as follows : 



About a week after I missed the delightful song, so I started to investigate. 

 Rapping on the stub no bird appeared, and I soon saw that the edges of the hole 

 were alive with small spiders. I took the stub down and examined it, and found 

 the nest swarming with these spiders. The birds in building the nest bad used 

 small twigs entirely and had thickly stuccoed them with the white egg sacs of a 

 species of spider, that had hatched before the wren had deposited her own eggs, 

 and instead of making a home for her young, she had unwittingly gathered together 

 a fine family of spiders and provided them with a well-sheltered retreat. 



Cats rank as enemy No. 1 of the house wren. Since these birds nest 

 about human habitations, especially on farms, where cats are common, 

 they fall prey to them oftener than do species of birds nesting in 

 remote localities. Cats are especially destructive to young when they 

 leave the nest prematurely. Reports of adults' falling victim to cats 

 are common, but young are always in imminent danger of the ravages 

 of these bird destroyers. I vividly recall seeing a cat seize two young 

 wrens in rapid succession when a brood of seven were startled from 

 the nest before some of them were able to fly well. The unfortunate 

 youngsters landed on the ground where a prowling cat was poised 

 for action. 



