Cattle grubs, the immature stage of heel flies, develop within the body of cattle.  Protection from and control of cattle grubs is achieved with avermectin products and dusts.  Carefully read insecticide labels prior to treatment.  Using an avermectin product at the in correct time could cause death of the animal due to a cattle grub infestation near the esophagus or spinal column of the animal.

Photo courtesy of C. L. Hoelscher