Big Fly (do'tsoh) (H), although apparently mythological, has a biological existence. A Tachinid fly of the species Hystricia pollinosa Van der Wulp (I am indebted to L. C. Wyman for the identification) it has the habit of lighting on a person's shoulder or chest just in front of the shoulder. It is of major importance in ritual since its powers supersede those of any of the deities for whom it acts. Big Fly is frequently a guardian of the east side of a sandpainting and, in paintings of the Hail and Wind chants, the insect is a major figure, often repeated.
Big Fly found Holy Man when he was captured by Thunder. Big Fly instructed the people about making offerings. Big Fly directed Holy Man after he had been struck by lightning and begged him not to go into dangerous places, explaining, "From now on I will help you. I once carried news to Monster Slayer. That was when the people had no one else to carry the word. Now that they have Dark Wind and Blue Wind as informers, they have delegated me to help you." Monster Slayer insisted upon going to forbidden places to find out what was going on and Big Fly said, "All right! Go ahead, but I will go with you." There was no place he did not know, and he traveled behind Holy Man's ear so he could warn and inform him (Reichard 1939, pp.61-3, PI. XII, XIII, XXII; 1944d, p. 37; Shooting Chant ms.; Newcomb-Reichard, p. 39, PI. XVI, XXI, XXII, XXXI; Haile 1938b, pp. 183-5; Matthews 1902, p. 260.
Navajo Religion, Vol II; Gladys A. Reichard, 1950