FIGURE 56.—Peeling brands attacked by screw worms.
Infestation of Young Animals
SCREW-WORM Invasion of South Necessitates Modified Farm Practices
The screw-worm problem in this country has been intensified by the spread of this pest into the Southern States during the summer of 1933. This insect is a native of North America, and it occurs in destructive numbers every year in the Southwestern States, where it is one of the most important problems of livestock raisers. All kinds of livestock, wild animals, and even man are attacked by this pest.
The screw-worm flies are bluish green with three black stripes on the back and reddish-yellow face. There are two species of these flies. One lays its eggs in fresh wounds on any part of the body, while the other breeds in carcasses of animals and in old wounds on livestock. The larvae, or worms, of both species soon hatch and penetrate the tissues, in which they complete their growth in about 6 days. Then they drop to the ground and there enter the pupal or resting stage, from which the adult fly emerges a few days later.
The invasion of the Southeastern States produced an acute phase of this problem, because the farmers in that region were unfamiliar with the insect and its depredations, and many of them were financially unable to deal adequately with the pest. Under these circumstances it is not surprising that a condition approaching hysteria resulted in many localities.
The pest appeared in northern Florida and southern Georgia in 1933 and caused considerable losses during the fall. In May 1934 infestations of all classes of livestock began to appear in this and adjacent territory. The ravages of the pest extended rapidly, and as the season advanced most of the State of Florida was involved and cases occurred in about 120 counties in Georgia and throughout the southern half of Alabama, Mississippi, and Louisiana. A good many cases also occurred in southeastern South Carolina, although the infestation there was not general. The belt of heavy infestation extended westward along the coastal area into southeastern Texas. A considerable number of animals in northwestern Iowa and some in central and southern Indiana were also infested with screw worms, but these appeared to be isolated areas of infestation. The pest is rarely found so far north.
It has not been possible to gather definite information on the number of screw-worm cases or the losses due to this outbreak in the Southeast, but it is evident that the total loss has been stupendous. In many of the coastal counties in Texas, Louisiana, Mississippi, and Alabama, the stockmen report that their loss among sheep has reached 30 to 40 percent of their holdings and that the loss among their hogs has been nearly as high. The infestation among cattle is stated to have attained 15 to 20 percent and that among horses and mules 5 to 8 percent. The percentage of infestation in many counties in Georgia and Florida is equally high. Extensive unfenced areas are pastured by sheep, cattle, and other stock in each of these States, and the losses have invariably been higher where the stock has been run on such open range.
One of the leading predisposing causes of screw-worm infestation in the Gulf States is the attack of the Gulf coast tick. This tick affects all kinds of animals, usually in the external ear, which soon becomes swollen and cracked, forming an ideal place for screw worms to attack. The exudate from the screw-worm-infested wound runs down into the ear and over the face, encouraging the flies to lay eggs upon and the worms to burrow into the more vital parts of the animal. In much of the screw-worm-infested territory, therefore, the control of the Gulf coast tick is an important step in dealing with the screw worm. The habits of this tick do not permit its eradication, or even satisfactory control, by dipping, as practiced in the eradication of the cattle tick. The application, with a swab, of pine-tar oil to the inner surface of the ears kills most of the worms and protects the animal from infestation for several days.
Another important cause of attack and consequent loss is the birth of young during the season when screw worms are active. During this outbreak many stock owners found that practically every newly born lamb, calf, and pig was attacked. In these young animals the navel or mouth is usually involved, and in the former location the burrowing maggots soon reach vital parts and cause the animal to die. In the Southeastern States branding (fig. 56), castrating, and marking have been carried on heretofore at any time the stock owner’s fancy dictated, and this practice has given rise to innumerable infestations. Large numbers of freshly branded and ear-tagged cattle shipped into the infested area in accordance with the Government’s drought-relief program became infested with screw worms, and this led many to believe that the pest was introduced from the West with these cattle. The fact that the insect was prevalent in the Southeastern States in 1933 and in the spring of 1934 before the drought-relief cattle were introduced clearly disproves this.
Many stock raisers in the Southeast have asserted that unless the screw worm is controlled they will be forced to abandon livestock raising. This statement has emanated chiefly from the large owners who have run their herds and flocks on open range. It seems certain that stock raising cannot be carried on profitably in the presence of screw worm conditions such as those existing in 1934 without decided changes in methods of management.Ranges must be fenced in order to enable the stock owner to check up closely on his stock and treat injured or screw-worm-infested animals promptly and regularly. The extreme importance of prompt treatment is emphasized by the recent discovery that there are two distinct species of screw-worm flies, one of which apparently breeds only in the tissues of living animals. Thus, if infested animals are not treated, this most destructive form may multiply until a pasture is heavily stocked with them.
The heavy infestation of newly dropped young in the summer and fall makes necessary the control of breeding time so as to avoid births during the most active fly season. This, in turn, demands fences to control the breeding stock and often the production of supplemental feeds to keep the dams in proper condition for dropping their young early in the spring.
The fencing of pastures invariably leads to the breeding of better animals, and the possession of more valuable animals demands better care of them; thus the whole industry is ultimately raised to a higher level.
The screw worm compels stockmen to brand, castrate, and mark their animals when flies are not abundant. A uniform breeding season aids in this, and fences are important.
To meet the urgent needs of the acute screw-worm situation that developed in the Southeast subsequent to the making up of the budget, and to permit the Department to carry on a control campaign, arrangements were made, with the approval of the Bureau of the Budget, for the transfer of $5,000 from an appropriation made to the Bureau of Entomology and Plant Quarantine for another purpose. This fund was used for the expenses of Department men in determining the status of the problem in the South and in directing the control work. To complete the organization and to provide some of the materials for treating infested animals, the Emergency Relief Administration in each of the States of Florida, Georgia, and Mississippi provided $7,500. An organization consisting of regional and county control directors was quickly built up in each of these States; and, as the need of familiarizing farmers with the proper methods of treating infested animals and protecting others from attack was apparent, an intensive educational campaign was undertaken in cooperation with the various interested Federal, State, and local agencies. Many meetings were held, in some of which demonstrations were conducted to show how to apply benzol to kill the worms and pine-tar oil to repel the flies, how to burn carcasses (fig. 57), to build treating chutes, etc. To acquaint stock owners with the proper materials for treating screw-worm cases, small quantities of benzol and pine-tar oil were given to those having infested herds, especially those unable to buy these materials. In this work an effort was made, not only to enable the farmers to meet the present problem effectually, but to teach them how to prevent the recurrence of such heavy losses as were experienced during this outbreak, and to improve farm practices so that livestock raising may be more profitable in the future.
