CATTLE GRUB

Background, section of tanned hide showing grub damage. A, Calf being chased by heel flies. B, Life cycle diagram showing eggs attached to, hair (greatly enlarged); b, small larvae; c. encysted larva and the hole in the, hide; d, puparium under litter, e, adult heel fly, (b, c, d, and e, all about natural size.)

CATTLE GRUB

The cattle grubs in the backs of cattle are the larvae of two species of heel flies. One, the common cattle grub, is found in most parts of the United States. The other, the northern cattle grub, occurs in the northern half of the country. It appears in the backs of cattle later than the common species. If both species are present the period from the first appearance of grubs in the backs of cattle until the last one has emerged from the tissues of the host may last about 5 months or longer. In some of the southern localities the grub season begins in late summer or early fall. In the northernmost States the season does not begin until in the winter or early spring.

The adults, or heel flies, lay their eggs on the animal during the spring and summer. The young grubs hatching from the eggs burrow through the body of the animal for about 9 months and finally become located under the skin of the back. They cut a hole through the skin, become encysted, and complete their development in the cyst in 5 to 7 weeks. The mature larvae drop to the ground and form a pupal case from which the heel flies later emerge. The cattle grubs have one generation a year.

The adults also injure cattle. The attacks of the heel flies frighten animals; often they cause stampedes that result in loss of flesh and milk and in mechanical injury. The grubs bore large holes in the choicest part of the hide and produce irritation, inflammation, subnormal development of young animals, and considerable loss of beef, milk, and leather.

Control: Rotenone is the only insecticide recommended for the control of cattle grubs. Finely ground cube or derris containing 5 percent of rotenone may be applied to the backs of cattle in the form of a spray, dust, or wash. Power spraying is the fastest way to treat cattle and is generally preferred for large range herds. The spray should contain 7 1/2 pounds of the cube or derris powder per 100 gallons of water. It should be applied at the rate of 1 gallon per animal. One should use a driving nozzle and a pressure of 400 pounds per square inch. Dusts are preferred by owners of small herds of cattle and are desirable for use in cold weather. Three ounces of a dust containing 1 part of derris or cube and 2 parts by weight of a suitable diluent should be used per grown animal. The dust must be well rubbed into the grub cysts by hand. The use of derris or cube wash when thoroughly applied with a stiff fiber brush gives excellent control of grubs. The wash should contain 12 ounces of derris or cube powder and one-fourth ounce of a wetting agent per gallon of water. From 1 to 2 pints per animal is needed for each treatment.

The correct timing of treatment, whatever method of application is used, is essential for good cattle grub control. The precise time of treatment in any given locality can be determined by the county agent or other experienced advisers.