﻿THE CATTLE GRUBS OR OX WARBLES 13 



productivity and. health of the host. When the larvse reach the 

 esophagus in numbers, however, marked irritation is often in evi- 

 dence. The submucous tissues are edematous, usually yellowish, and 

 sometimes bloody in the region of the larvse. Cases are on record 

 in which heavy infestations of the esophagus produced eclematose 

 conditions with large swellings. Instances are also recorded in 

 which the larvae burrowing along the spinal canal have caused 

 l^aralysis of the posterior parts, although this seems to be unusual, 

 considering the large number of cases in which infestation of the 

 canal occurs. 



Abundant testimony is at hand as to the injurious effect of the 

 last-stage larvse under the skin in the backs of cattle. Many stock- 

 men believe, and their opinion in most cases seems well founded, 

 that hea^y infestations of the grubs in the backs of calves are a 

 prime factor in causing their death. It has been observed repeatedly 

 that where these larvse are removed, -the calves begin to " pick up " 

 l^romptly. The effect of heavy infestations in the backs of dairy 

 cattle is also responsible for decreased milk flow. Danish literature 

 contains a reference to a case observed by Boas {6), in which a 

 cow producing daily from 30 to 32 pounds of milk increased the 

 yield to 40 pounds a few days after 80 larvse had been extracted 

 from the 'back. Feeders frequently comment on the difficulty of 

 fattening animals in which a considerable number of grubs are 

 present. Those who feed steers on an extensive scale during the 

 winter have informed the writers that in most cases when an animal 

 is not making proper gains, it will be found upon examination to 

 have a heavy infestation of grubs in the back. When these are ex- 

 tracted the animals usually respond well to the feed. Exact in- 

 formation on this subject is meager. Schottler and Glaser (88) 

 have reported upon an experiment which they performed in Ger- 

 many on the effect of grubs on the fattening of cattle. The grubs 

 were extracted from one-half of the herd and the other half kept 

 as a check. The portion from which the grubs were removed showed 

 a gain in weight of 5.16 per cent over the infested portion of the herd. 



Aside from the damage produced by the holes cut in the skin, 

 there is other injury produced to the host itself by the grubs while 

 located in the subdermal tissues of the back. When the young larvse 

 first reach the subcutaneous tissues along the back, marked swellings 

 are often produced. These are evidently painful, as indicated by 

 the action of the host when they are touched. Just how much irri- 

 tation is produced after this is problematical. Undoubtedly the 

 spiny armature of the fourth and fifth stages causes considerable 

 irritation, but it is supposed that the encystment sac surrounding the 

 larger larvae is practically free from nerves, and for this reason 

 the host probably does not experience any considerable amount of 

 ];ain or annoyance. Not infrcijiicntly, however, jjus organisms gain 

 entrance to the openings, and often large abscesses are formed under 

 the skin. Those are associated usually with the death of the larva, 

 either by crushing or by its inij>risoniuent and suffocation fi'om the 

 firm plugging up or scabbing over of the hole in the skin. In a 

 number of instances abscesses have been observed which were half 

 as large as the crown of a man's hat and vei-y sore. If these are 

 well opened and drained they soon heal, but where they are not 



