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BULLETIN" 1369, U. S. DEPARTMENT OF AGRICULTURE 



in the North, the term " northern cattle grub " is suggested for this 

 species; and since FI. lineatum is abundant and widely distributed 

 throughout the countrj^ it may be termed the " common cattle grub." 

 When referring to the adult the word " fiy " could be added after 

 either of the names and thus the habits of the larvae would be sug- 

 gested ; but the well-established term " heel fly," with the modifying 

 words " northern " or " common " preceding it when it is desired to 

 refer definitely to one species, is preferable. 



The most prevalent idea as to the cause of the grubs in the backs 

 of cattle is that the animals are stung by the large black horse fly 



{Tdbanus atratus Fab.) (fig. 

 4). This idea originates 

 from the observation that 

 these flies attack the cattle 

 primarily . along the back 

 where the grubs occur and 

 that they annoy the stock 

 considerably. A good many 

 stockmen are of the opinion 

 that the running of cattle in 

 the s]3ring is caused by the 

 pain produced by the grubs 

 in the back, especially at 

 the time they are dropping 

 out. This erroneous suppo- 

 sition is, of course, corre- 

 lated with the fact that the 

 heel flies are seldom seen in 

 action, owing to the rapidity 

 with which the cattle leave 

 a spot when the heel fly 

 appears. There are many 

 different notions held by 

 stock raisers as to how grubs 

 get into the backs of cattle 

 and what causes them. These 

 are often colored by the theories propounded by naturalists as 

 reviewed in the preceding historical sketch. 



HOSTS 



The normal host of Hypoderma hovis and H. lineatimi is cattle, 

 Bos taurus. The American bison. Bos hiso7i, is known to be infested 

 at times with II. lineatuvi^ but bison do not appear to be so heavily 

 infested as are cattle raised under similar conditions in the same 

 regions. The migration and development in bison appear to be 

 practically the same as in cattle. 



A number of reports are at hand of the occurrence of H. lineatum, 

 larvse in the subdermal tissues of the backs of horses. A few speci- 

 mens of larvae from this host have been examined by the writers and 

 found to be H. lineatum. Most of those seen were m the^ fifth stage. 

 Stockmen have informed the writers that occasionally one of their 

 cow ponies becomes infested with as many as 10 or 15 grubs. These 

 sometimes produce abscesses, probably due to the crushing of the 



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Fig. 4. — The black horse-fly (Tahanus atratus), 

 often erroneously thought to be the cause of 

 cattle grubs. Much enlarged 



