Horn flies, Haematobia irritans irritans (Linneaus) (Diptera: Muscidae) were reared in vitro using cattle, pig, horse, rabbit, sheep, goat or chicken blood. The highest survival, bloodmeal size and rate of ovarian development were recorded for both female and male flies fed cattle blood. Flies fed pig, rabbit, sheep and goat blood showed intermediate survival. Flies fed chicken blood showed the lowest survival rates, ingested the smallest bloodmeals and did not develop ovaries. The relationship between dietary factors and host specificity of the horn fly, and the efficiency of vertebrate blood source of several animals for laboratory colonization of horn fly are discussed.