62 BULLETIX 1089, V. S. DEPARTMEiSiT OF AGEICULTURE. 



been captured as late as September 9, so that its season of activity 

 covers three months in favorable years. Being an arctic species, it 

 can withstand much more cold and wet than southern species of 

 warble flies. The eggs are laid mainly on the fine, woolly hairs 

 which constitute the under down of a reindeer coat, principally on the 

 parts which come in contact with the soil when the animal lies down ; 

 this means the flanks, brisket, and the upper part of the legs. 



Tlie fly lays its eggs both when reindeer are standing and lying 

 down. When it lays on standing animals it causes them much uneas- 

 iness, and during hot weather it is common to see a herd " milling " 

 or moving round and round in circles. Some of the animals will be 

 seen running, others kicking and stamping; meanwhile the fawns 

 will be uttering their grunting plaints of oh-oh-oh. The whole scene 

 gives the impression of worry and unrest and makes one feel as the 

 great Linnaeus did when he first saw these flies at work in Lapland, 

 that even a small insect can bring much trouble into the world. 

 Fortunately, the warble fly does not always keep the animals so restless. 

 T^Tien the herd is resting the flies adopt gentler tactics, and they may 

 be seen on the ground busily depositing their eggs on the reindeer 

 hair without causing any annoyance other than, perhaps, a slight 

 tickling at times. In this case the insect backs up, gently pushes its 

 long ovipositor into the hair, and lays its eggs without necessarily 

 alighting on the deer. 



Experimentally, the eggs have been found to hatch in 6 to 7 days, 

 and the young lars*ae to bore through the skin. Though this act of 

 boring has not been witnessed in reindeer, there is no doubt that the 

 grubs do go through the skin. They have been found in large num- 

 bers just under the skin, and as many as 107 were counted on one hind 

 and one front leg of one animal. These young grubs are very minute, 

 and numerous examples about 1 millimeter in length were found. 

 The grubs may be found on the legs and body quite early in the 

 season, and in 1921 they were seen as early as August 4. 



There is a definite migration of the larvae from the point of en- 

 trance toward the back.^^ The first grubs to reach the back and 

 bore through to the outside were found on September 26. These 

 were two in number. A week or two later hides may be found with 

 numerous punctures. It is not until toward the end of October 

 that the holes through the skin attain any size. However, even the 

 smallest hole causes an irreparable injury when a skin is tanned. 



" In an unpublished report of 1914, .Toss recorded the finding of two small warble 

 larvae along the gullet. This is of interest in that in the present investigation larvae 

 were not encountered in this position. In Bergman's investigations in Sweden there are 

 no records of the larvae being found inside the body cavities. It is possible that the 

 larvae which .Joss found may have been erring or lost. In the present investigation in 

 Alaska, larvae were encountered deep in the muscles, having evidently taken a wrong 

 course in their migration to the back. 



