REINDEER IN ALASKA. 63 



-The larvae grow progressively and evenly in size until May, and 

 lie earliest grubs emerged (1921) on May 12. It is quite likely that 

 very few may come out prior to this date, and not many are left 

 ehind in the skin on July 1. The time of greatest emergence of 

 rubs is during June. 



The larvae pupate, or harden, in a day or two, depending 

 pon the state of moisture surrounding them. There are no satis- 

 ictory records for Alaska as to the average period required for 

 16 emergence of the fly. In trials which were made in 1921, the 

 upae were kept too moist, owing to unavoidable circumstances, so 

 lat though a few of the flies emerged, they did so after alength- 

 led interval. Bergman states that in Sweden the pupal stage aver- 

 ^es about 27 days.^^ No doubt in Alaska it will be found that the 

 eriod is of similar length. 



The damage done by warble flies is difficult to estimate. In 



laska, though reindeer are sometimes burdened with several hun- 



red larvae in their backs, and in rare cases may have as many as 



'thousand (PL XXIV), it seems that there is considerable toler- 



ice of the parasites by the animals. In other words, the reindeer 



itpport a large number of warble larvae without showing much 



differing or loss of condition. That there is a defensive reaction on 



e part of the reindeer against the grubs is shown by the fact that 



e yearlings have the most larvae, but when they reach 3 jescrs of 



;e it often happens that they have only a few grubs, and when 



iult life is reached at 5 or 6 years they may escape altogether. 



be reaction on the part of reindeer to warble larvae is mani- 



: sted by the formation of pus and by the production of a sac which 



closes the grub after it has taken up its permanent place of abode 



I the back. The amount of pus secreted is not so great as is that 



creted by cattle against Hypoderma, the cattle warble-fly. 



Reindeer skin is very thin and the larvae make a large opening 



the time they are ready to leave the body. These openings, to- 



ther with the presence of pus, expose the yearling reindeer, 



' ^ecially, to the attacks of screw worms. It has been found that 



is a very simple matter to extract the larvae by squeezing the skin. 



' lis causes the reindeer little pain and the operation is quickly 



' ne. If the yearlings were thus treated in April and May, danger 



ii)m screw worms would be eliminated almost entirely, as the cavi- 



l!S in the backs would have healed before the blow flies appear, 



lich is at a later date. 



The suggestion has been made that does be separated from the rest 

 ( the herd at fawning time. When this is done, the bucks and 



' Bergman, Arvid, On the Oestridae of reindeer : Entomologisk Tidskrif t, vol. 38, pp. 

 12, 113-146, 1917. 



