62 BULLETIN 1089, U. S. DEPARTMENT OF AGRICULTURE. 
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. 
The 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. 
When 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 larvae 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. 17 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. 
17 la an unpublished report of 1914, Joss 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. 
