SCREW-WORMS AND OTHER MAGGOTS. 



Cows frequently are infested on regions where blood collects at the 

 time of calving. Where ticks are abundant, a common source of 

 infestation is through the deposition of eggs on blood spots resulting 

 from the crushing of engorged ticks. Most of the other infestations 

 occur following surgical operations such as dehorning, castration, 

 branding, etc. Some cases follow serious attacks of biting flies such 

 as the horn fl}', stable fly, and horseflies. The blood oozing from the 

 punctures made by these flies attracts the screw-worm fly. Among 

 hogs the worms usually gain 

 entrance about the ears and 

 head through scratches made in 

 fighting. 



In cases which are not treated 

 the injury is gradually made 

 worse by repeated laying of 

 fresh eggs, the number of mag- 

 gots being increased enormously. 

 In such instances the animals 

 lose appetite immediately, be- 

 come emaciated, and hide away 

 in the brush or some out-of-the- 

 way place. This habit increases 

 the chances of loss by death, 

 especially where the ground is 

 covered by heavy chaparral. 



While the death of animals is 

 not infrequent, the major por- 

 tion of the loss is due to the re- 

 duction of flesh, the time required for riding ranges and treating ani- 

 mals, and the money spent for screw-worm medicines. During the 

 summer of 1914 the screw worms were so bad that many ranchers 

 employed from 1 to 10 extra men, who were kept busy almost con- 

 tinuously on this line of work from May to November. A further 

 loss of no small amount results from the practical prohibition of the 

 breeding of cattle in certain districts, especially in parts of south- 

 western Texas, where stockmen have practically discontinued the 

 attempt to raise calves and are buying up yearlings or other older 

 animals and bringing them in for grazing. 



DESCRIPTION OF THE SCREW-WORM FLY AND ITS OFFSPRING. 



All flies pass through the following four changes in the course of 

 their lives: (1) The adult or mature insect, (2) the egg, (3) the 

 larva, which is known as the maggot or worm, and (4) the pupa, 

 which is an inactive stage in which the change from the maggot to 

 the adidt fly takes place. The pupa stage corresponds to the chrysalis 



-Screw-worm fly as seen from above. 

 Much enlarged. 



