20 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
in the North, the term “northern cattle grub” is suggested for this 
species; and since //. /ineatum is abundant and widely distributed — 
throughout the country it may be termed the “ common cattle grub.” — 
When referring to the adult the word “fly ” could be added after 
either of the names and thus the habits of the larve 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 | 
(Tabanus 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 spring 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 | 
IG. 4.—The black horse-fly (Vabanus atratus), stock raisers as to how grubs | 
ontte arabs. Mach elarged -<-pet inte the backs solve ae 
and what causesthem. These | 
are often colored by the theories propounded by naturalists as | 
reviewed in the preceding historical sketch. | 
HOSTS 
The normal host of Hypoderma bovis and H. lineatum is cattle, § 
Bos taurus. The American bison, Bos bison, is known to be infested | 
at times with 77. lineatum, 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 @ 
larvee in the subdermal tissues of the backs of horses. A few speci- | 
mens of larvee from this host have been examined by the writers and | 
found to be H. lineatum. Most of those seen were in the fifth stage. § 
Stockmen have informed the writers that oceasionally 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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