In the United States there are two species of ox-warble flies, technically known as hypoderma lineatum and hypoderma bovis.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
In hypoderma virgultorum, H. commune, and H. scirpinum, the spermogonia are small depressed black capsules, which contain an abundance of minute spermatia.
"Fungi: Their Nature and Uses"
Mordecai Cubitt Cooke