tates. The tail is orange-yellow, lighter in color than that of the other
species, and the legs have but few hairs. This fly commonly deposits its
eggs on the outside of the hind quarters and above the fetlocks when the
animals are moving, or lower down if they are quiet. Cattle are usually
much disturbed by the activity of this fly and not infrequently appear
terror stricken. The eggs are attached singly, one egg to a hair near its
base.

The eggs of the warble flies hatch as a rule in about a week, the time
varying with local conditions. The young warble is about 1 mm. (1/25 inch)
long. It crawls to the base of the hair and burrows into the hair follicle.
The entrance of the larvae frequently causes sudden appearance of swellings.
The larvae of _H. bovis_ in entering the skin rarely cause a flow of serum
or pus formation, but those of _H. lineatum_ commonly cause a considerable
flow of serum with pus formation resulting in a matting of the hair on
affected areas of the skin. The warbles after penetrating the skin migrate
through the body and ultimately reach the backs of the cattle, _H.
lineatum_ usually appearing there in northern latitudes about the middle of
December and _H. bovis_ about a month later. During their migrations,
before they reach the back, the young warbles spend a considerable period
in the walls of the esophagus, or gullet, and may be found in this location
as early as August 15. During the fall and winter a large proportion of the
gullets of cattle that are slaughtered are found to be infested with
warbles, and are known as grubby gullets or weasands in the packing houses.

When the warbles first appear in the back they are about 3/5 inch long.
They cause swellings about the size of pigeons' eggs, each swelling having
a small hole in the center, which has been punctured in the skin by the
warble to enable it to breathe. Through this hole the warble leaves the
back of the cow when it has completed its parasitic stage of development,
at which time it measures nearly an inch in length.

The full-grown larvae begin to leave the backs of the cattle early in the
year, and in northern latitudes the last leave before the middle of July.
After leaving the backs of the cattle they burrow into the ground, lie
quiescent for about a month, and become transformed into mature flies. In
northern latitudes the mature flies of the species _H. lineatum_ may be
observed during April and May, and those of the other sp