From the June 14, 1907 Gillette News:
Nearly a thousand yearling ewes which ranged on Casper and Wallace creeks last winter have died during the past few weeks from grubs in their heads and there seems to be no cure for them. Art Gaylord is probably the heaviest loser, 250 having already died out of his bunch and other flock masters have lost from 100 to 200, and the loss continues, it is stated, at the rate of from 12 to 15 head every day. It is supposed that these sheep got into a bunch of a certain kind of fly, which lodged in the nostrils of the sheep and after a few months turned into a grub. The grub then worked its way into the sheep’s brain, which caused the sheep to die.