PARASITIC DISEASES OF CATTLE IN PUERTO RICO 2^ 
herds, the fly can he controlled by scattering all of the fresh drop- 
pings in the yards and pastures with a rake or other implement. 
The scattered 'manure dries out rapidly and the larvae die for la«'k 
of the moisture required for their development. Hogs and poultry 
assist in control by scattering the droppings and by eating the 
maggots. 
OTHER EXTERNAL PARASITES 
Common scab or " soma" of cattle. — The mange mite (Psoroptes 
communis) (fig. 2. M) is found on the surface of the skin. It is a 
very small animal, which may be seen with the naked eye if placed 
on a dark background. Psoroptic mange is comparatively common, 
but in the climate of Puerto Rico it rarely becomes a serious disease. 
However. heav} r infestations have been found among animals which 
were crowded together in small enclosures. The mite pricks the skin 
and sucks the blood serum. The first symptom noticed is itching, 
and later there is formation of scales and scabs and thickening of 
the skin. 
Dipping or spraying with the lime-sulphur dip and the nicotine 
sulphur dip are effective remedies for this mange. Proprietary 
brands of these preparations, ready for use, are available. Cattle 
which are dipped regularly for ticks do not become infested with 
this kind of mange mite. For eradication of the mange the treat- 
ments must be repeated at intervals of 10 days. Two dippings may 
usually be depended on to cure ordinary cases. Four or more dip- 
pings may be necessary in chronic cases. After treatment the pens 
or stables housing the infested animals should be left vacant for a 
time or should be cleaned and disinfected with a strong solution of 
cresol to destroy the stray mites. Experiments carried out by the 
Bureau of Entomology. United States Department of Agriculture, in 
cooperation with the Texas Agricultural Experiment Station have 
shown that the longest period during which a pen remained infective 
was 10 days. 
Sarcoptic mange caused by another variety of mite also occurs in 
cattle. This mite burrows into the skin, usually in locations where 
the skin is tender and the hair is thin. This disease is more serious 
than common scab because it is more severe in its effects and more 
difficult to eradicate. Sarcoptic mange of cattle is a rare disease, 
but local veterinarians report that infestations have occurred. The 
treatment is the same as given for psoroptic mange but it requires 
persistent, thorough, and frequent application of these preparations. 
A veterinarian should be consulted if the presence of this mange is 
suspected. 
The screw worm. — The screw worm (Cochliomyia arm ricana) (fig. 
2. L) is the maggot of a blowfly which may attack any open wound 
of animals. The fly itself is not often noticed, but the maggots of 
this species are distinguished from the larvae of other common blow- 
flies by their habit of penetrating practically sound tissue. The fly 
deposits its eggs in wounds, in masses of from 40 to 250 eggs. These 
eggs hatch in 3 hours or less and the maggots burrow into the wound 
and grow rapidly and become completely developed in 4 or 5 days. 
The injury is due to the eating away of the tissues and also to toxic- 
secretions produced by the maggot. There is also serious danger 
