Worms in the Backs of Cattle

Worms in the backs of cattle are actually grubs, also called warbles and wolves. Two species occur in the United States and Canada: the common cattle grub and the northern cattle grub. The common cattle grub is the larva of the heel fly and the northern cattle grub is the larva of the bomber fly.

  1. Symptoms and Effects

    • Grubs present in a cow's back cause the skin to swell and form warbles. These insects cause cattle to lose weight and are responsible for reduced weight gain, poor meat quality, decreased hide value and bad milk production. Most meat processors discount cattle with five or more grubs. Losses in livestock production in the United States due to grubs are estimated at $160 million per year.

    Life Cycle of the Common Cattle Grub

    • Heel flies lay five to 15 eggs in a row on the hair of a cow's legs and lower body in late winter and spring. Larvae hatch from the eggs, cut holes through the skin and migrate to areas around the cow's esophagus. In the fall, grubs move to the animal's back, cut breathing holes in the skin and remain there during the winter. The larvae or grubs emerge from the animal's back in the spring, fall to the ground and pupate. The adult emerges from the pupa and the life-cycle is repeated.

    Life Cycle of the Northern Cattle Grub

    • Like heel flies, bomber flies lay eggs on the legs and belly of an animal, but deposit only one egg per hair. Larvae that hatch from the legs bore through the skin and migrate directly to the spinal column. The rest of their life cycle is the same as that for the common cattle grub.

    Control

    • Several systemic insecticides are available for grub control at livestock supply stores. These products can be applied to cattle as a pour-on, spot-on, spray or injection. A pour-on is applied by pouring the insecticide along the cow's spine from the front shoulders to the tail head. Specially designed guns are used to apply the spot-on insecticide in measured dosages directly to the animal's skin. When spraying, it is important to wet each animal thoroughly using a livestock sprayer set at 300 to 400 pounds per square inch pressure. Injections are applied under the loose skin immediately behind or in front of the animal's shoulder. The insecticides should be applied in mid-summer to early fall before migrating grubs reach the esophagus area or the animal's back to avoid toxic reactions.