The common cattle warble fly will lay 10-15 eggs at a time and deposits them in a row along the hair shaft, egg laid against egg. The larvae of the northern cattle grub will migrate up the legs through the space between the vertebrae and the spinal cord and eventually into the tissue beneath the skin of the back. On the ground, the grub continues to develop and, depending upon weather conditions, evolve into an adult warble fly within 1 to 3 months. The life cycles of the two species of grubs, depending on the climate, take about 9 to 12 months to complete. Cattle have been know to break through fences and run blindly for extended periods of time.
Economic losses are, however, much more important.
Milk production may be reduced and weight loss resulting from the wild efforts of the animals to escape the flies is considerable. The value of the carcass depreciates because of the flesh surrounding the grub becomes greenish yellow, jellylike in appearance and must be trimmed away before the carcass can be passed for food consumption. In addition, the value of the hide is reduced because of the holes cut in the skin by the larvae. Because of the above reasons, and probably several more, grub control becomes and important item in beef cattle management. Cattle warble control is aimed at killing the grub rather than preventing the adult fly from laying eggs.