REINDEER IN ALASKA. 63 
The larvae grow progressively and evenly in size until May, and 
the earliest grubs emerged (1921) on May 12. It is quite likely that 
a very few may come out prior to this date, and not many are left 
behind in the skin on July 1. The time of greatest emergence of 
grubs is during June. 
The larvae pupate, or harden, in a day or two, depending 
upon the state of moisture surrounding them. There are no satis- 
factory records for Alaska as to the average period required for 
the emergence of the fly. In trials which were made in 1921, the 
pupae were kept too moist, owing to unavoidable circumstances, so 
that though a few of the flies emerged, they did so after a length- 
ened interval. Bergman states that in Sweden the pupal stage aver- 
ages about 27 days. 18 No doubt in Alaska it will be found that the 
period is of similar length. 
The damage done by warble flies is difficult to estimate. In 
Alaska, though reindeer are sometimes burdened with several hun- 
dred larvae in their backs, and in rare cases may have as many as 
a thousand (PL XXIV), it seems that there is considerable toler- 
ance of the parasites by the animals. In other words, the reindeer 
support a large number of warble larvae without showing much 
suffering or loss of condition. That there is a defensive reaction on 
the part of the reindeer against the grubs is shown by the fact that 
the yearlings have the most larvae, but when they reach 3 years of 
age it often happens that they have only a few grubs, and when 
adult life is reached at 5 or 6 years they may escape altogether. 
The reaction on the part of reindeer to warble larvae is mani- 
fested by the formation of pus and by the production of a sac which 
incloses the grub after it has taken up its permanent place of abode 
on the back. The amount of pus secreted is not so great as is that 
secreted by cattle against HypoderrrKi, the cattle warble-fly. 
Reindeer skin is very thin and the larvae make a large opening 
at the time they are ready to leave the body. These openings, to- 
gether with the presence of pus, expose the yearling reindeer, 
especially, to the attacks of screw worms. It has been found that 
it is a very simple matter to extract the larvae by squeezing the skin. 
This causes the reindeer little pain and the operation is quickly 
done. If the yearlings were thus treated in April and May, danger 
from screw worms would be eliminated almost entirely, as the cavi- 
ties in the backs would have healed before the blow flies appear, 
which is at a later date. 
The suggestion has been made that does be separated from the rest 
of the herd at fawning time. When this is done, the bucks and 
18 Bergman, Arvid, On the Oestridae of reindeer : Entomologisk Tidskrift, vol. 38, pp. 
1-32, 113-146, 1917. 
