SB
818

e578

ENT

No. 25, SECOND SERIES.

nited States Department of Agriculture,

DIVISION OF ENTOMOLOGY.

THE OX WARBLE.,
(Hypoderma lineata Villers.)
GENERAL CHARACTERISTICS AND ORIGIN.

One of the worst insect enemies of cattle, especially in the great
erazing regions of the West and Southwest, is the so-called ox bot,
or ox warble. It bears, also, a number of other colloquial designa-
tions, such as the ‘‘ox wormal,” “bot-fly,” “heel fly,” and is often
known merely as the ‘‘grub.’’ With reference more particularly to
the injury occasioned by it, we have the terms ‘grubby cattle,”
“warbled stock,” and the expressions ‘licked beef,” or ‘‘jelly,” in
description of the peculiar appearance of the region infested on the
beef and on the hides.

This insect (fig. 1) belongs to the
family Céstride, which includes the
gadflies and bot-flies, various species
of which affect all of the larger her-
bivorous mammals, some of them living
in the cavities of the body, as in the
nostrils and the digestive tract, and
others beneath the skin, as is the case
with the species under discussion. Un-
til comparatively recent years the gen-
eral belief has been that our ox bot-fly
was the common warble fly of the Old
World (Hypoderma bovis, fig. 2), but it
has been more recently shown that the
only bot-fly affecting cattle so fardis- . Oe TE a
covered in this country is a different Shee ee ae
species (Hypoderma lineata). This spe-
cles is also quite abundant in Europe, where it occurs in company with
the old species HZ. bovis, and often on the same animal. The /Typoderma
lineata is a common cattle pest throughout the United States, and
infests also the buffalo. In Europe it has been found from England to
the regions of the Balkans and the Caucasus. Whether it is of European
or American origin can not be very readily determined. It was present

323596—No. 25—06

2

in this country at a very early date, and may have been the charac-
teristic bot-fly of our native buffalo and have been introduced into
Europe from this continent. Its great abundance, however, on our
domestic cattle, and its wide range in Europe, leave its origin open
to doubt. It is rather remarkable, on the other hand, that the
Hypoderma bovis has never been found in this country, occurring,
as it does, rather commonly in Europe. Nevertheless, of the many
hundred larvee examined in this country by experts all of them have
proved to be lineata, and all of the captured and reared adult insects
of this nature in the various collections which have been examined
prove to be of this species. At the present time, therefore, so far as
known, no larve or adults referable to bovis have been collected on
this side of the Atlantic.

AMOUNT AND NATURE OF DAMAGE

Some years ago a careful investigation of the percentage of cattle
infested with the ox bot in this country was made by a western farm
paper. From the averages reported from the chief cattle States of
the Mississippi Valley it was shown that
50 per cent of the cattle received in the
Union stock yards at Chicago during
the grubby season, which includes the
months from January to June, were in-
fested and more or less injured by the
presence of the larvee of this insect.
The depreciation in the value of hides
from this cause was estimated at more
than a half-million dollars on the cus-
tomary reduction of a dollar fora grubby
hide. Adding to this the loss from the
-depreciated quality of the beef, together
with the lessened quantity of the same from the inferior condition of
affected animals, a total loss during the season in question was esti-
mated at over three million ieileas

The appearance known as “licked beef,’’ which results from the
presence of the grub, and which may be described as a moist or run-
ning surface of a greenish-yellow color, frequently presenting a frothy
or jelly-like appearance, is sufficient to condemn it for use in all first-
class hotels and restaurants.

~The effect upon dairy animals has been estimated by Mr. T. D.
Curtis at a shrinkage of from 10 to 20 per cent of the normal yield.
In England Miss Ormerod has made an estimate of the loss resulting
from the presence of the larve of the Hypoderma bovis, basing her
figures on reports from various practical men, showing a depreciation
of from £2,000,000 to £7,000,000 sterling per annum, or as much as

Fia. 2.—Hypoderma bovis—enlarged
YI
(after Brauer).

3

£1 per head of horned cattle. This loss is shown to fall very largely
on the cattle owners and also, to a less extent, on the butchers in
the depreciation of the value of the carcass.

These figures seem very large and startling, but the loss is of such a
nature and so widely distributed that, until comprehensive statistics
like the above are collected, the amount of damage annually suffered
is hardly appreciated. The losses are sufficient, at any rate, to indi-
cate that the cattle interests have few worse enemies than this bot-fly.
Before entering upon the subject of remedies, the habits and life his-
tory of the insect will be briefly detailed,

LIFE HISTORY AND HABITS.

It was formerly believed that the parent bot-fly deposited its eggs on
the backs of cattle, on the hair, or attached them to the skin, and that

Fia. 3.—Piece of warbled hide—warbles about half size (after Ormerod).

the young larve on hatching burrowed through the hide and gradually
developed until they attained full growth in a cell formed by them in
the connective tissue immediately beneath the skin. Dr. Cooper Cur-
tice, who has made very careful and interesting studies of the life his-
tory of this insect, has shown that an entirely different course is fol-
lowed. The facts obtained by Doctor Curtice have been supplemented
by investigations, more particularly of the egg-laying habits and first
stages of the larvee, conducted through the agency of this Division.
Briefly, the life habits of this insect are as follows:

Very early in the spring, as early as January or February in south-
western Texas and later northward, the flies begin to appear about

4

cattle and frequent their legs, and especially the region just above
the hoof, for the purpose of oviposition. It is from this common habit
of placing their eggs on the part of the body noted that they get the
name in the South and West of ‘‘heel fly,” and it may be for this reason
in part that cattle almost invariably seek running water in which to
stand to protect themselves from the fly. Furthermore, the fly seems _
not to approach the animals while standing in or over water, even if
the parts where the eggs are likely to be placed are above water, as
with animals standing on exposed rocks in streams.

The eggs are also placed occasionally, if not frequently, on other
parts of the body, asthe flanks and lower portions generally. In
one instance a correspondent observed an old and feeble animal, which
had lain down and could not get up to escape, attacked by some fifty

Fia. 4.—Portion of inside of tanned warbled hide (after Ormerod).

flies, which were observed about her at one time. A dozen or more of
these flies were afterward captured and submitted to us for identifica-
tion, together with a large number of eggs, from which our illustrations
were made.

Along the Pedernales River cattle would come to the water to
escape the flies as early as 9 o’clock in the morning and remain there,
for the most part standing on exposed rocks in the stream, until 5
o’clock in the evening. In the meantime the flies were observed along
the banks of the stream in extraordinary numbers, but none of them
seemed to care to approach the cattle.

One of the most noticeable features connected with the presence of
this fly among cattle is the intense excitement which it causes, often
amounting to frenzy, stampeding the stock and causing them to run
violently through shrubbery or to water where the fly will not follow

5

them. This can not come from any pain caused by the placing of the
eggs on the animals, but must be from an instinctive dread of the
insect, and is analogous to the similar frantic actions of the horse when
approached by the throat bot.

The injury to fattening range cattle in the spring is due very largely
to the annoyance occasioned by the presence of the fly. A Texas
correspondent, Mr. George W. Holstein, calls attention to this fact as
follows: ‘A cow quietly grazing will suddenly spring forward, throw
up her tail, and make for the nearest water at a headlong gait. Seem-
ingly deprived at the moment of every instinct except the desire to
escape, she will rush over a high bluff if in the way, often being killed

eth hg
EAN Oa
Ce a ay

Fig. 5.—Hypoderma lineata: a, eggs attached to hair; b, c, d, dorsal, ventral, and lateral view of egg;
e, embryonic or first larva, as seen in egg; f, g, mouth parts of same enlarged; h, anal segments of
same still more enlarged (from Insect Life).

by the fall. This, with miring in water holes and the fact that cattle
are prevented from feeding, causes the loss.”

As observed in the act of egg-laying, the flies approach the cattle
very swiftly, being almost too quick in flight to be observed except
at the very moment of placing the eggs. The eggs are fastened to
the hairs, in the examples received here, usually four to six together.
The structure of the lower portion of the egg is of such a nature that
it clasps the hair almost entirely and forms a very firm and strong
attachment. The peculiar shape of the egg is shown in the illustra-
tion (fig. 5). In length it measures about two millimeters, and is of
a dull yellowish-white color. The ovipositor, extended as in the act
of placing the egg, is represented in fig. 6.

The eggs once in position, the larvee probably rather than the eggs,
are carried into the mouth by means of the licking of the leg and the

6

region about the hoof and flanks of the animal. As seen from the
examination of our material, the egg, as soon as deposited, has the
larva already formed in it, and it is probable that the young larva

| escapes from the egg at the moment it is con-
\' veyed to the mouth, the pressure and moisture
of the tongue facilitating its escape. The egg,
at any rate, splits readily at the anterior end,
and the young larva being conveyed into
the mouth soon penetrates the esophagus by
means of its strong spines, which are repre-
sented in the illustration (fig. 5,e,h). These
young larve have been found in the walls of
the esophagus, and it is not until about the
end of December that they appear in any
numbers in the back.

After penetrating the esophagus the larva
soon moults and assumes a nearly smooth sur-
face (fig. 7), and for several months wanders
through the connective tissue of its host between the skin and the
flesh, penetrating gradually along the neck and ultimately reaching
a point beneath the skin in the region of the back. In the meantime
all traces of the larvee or attending inflammation disappear from the
region of the esophagus. The “lick,’’ according to
Dr. Curtice, is nothing more than an effusion of
serum in the connective tissue caused by the inflam-
mation induced by the wanderings of the young
erubs.

When the final position in the back is reached,
the larva moults again, becomes more spiny, and
penetrates or bores a hole through the skin, caudal
end first, through which it gets air for respiration
at this stage. At this time the anal spiracles, or

Fia. lineata—

6.— Hy poderma
ovipositor of female; a, from
side; b, tip, from below—en-
larged (from Insect Life).

breathing pores (fig. 8, d,/), are much more promi-
nent than they were during the long period of the
wandering life of the larva, when respiration must
necessarily be very limited. The larva now develops
much more rapidly, subsisting on the pus and bloody
serum which its presence beneath the skin induces.

The final moult soon follows, which brings it to the.

form that iscommonly seen by stockmen (fig. 8, g, 7).
When full grown, the larva has a length of more

Fig. 7.—Hy poderma
lineata—second
stage of larva from
esophagus; a, larva;
b, enlargement of

cephalic segments,
end view; c, mouth
parts; d, enlarged

end view of anal seg-
ment, showing spira-
eles and spines (from
Insect Life).

than an inch and is rather robust and of a yellowish-white color. It

works its way out by means of its strong spiny covering through the
hole whichit has previously used as a source of air, drops to the ground,
which it may or may not enter, but, at any rate, contracts and hardens,

i a al

7

and gradually darkens, ultimately becoming almost black in color.
This contracted and hardened larva is what is known as the puparium,
which, except for its changed color, texture, and shape, preserves all
of the characteristics of the larva. From three to six weeks later the
perfect fly escapes by pushing off a sort of circular piece or cap at
one end of the puparium. ‘The illustration (fig. 9) represents this
stage in the allied species, bovis.

The establishment of the wandering habits of the larva in its early
stages and the fact of its entrance into the animal through the mouth
and esophagus, instead of the skin of the back, is based on careful
experiments and examinations conducted by Doctor Curtice, and is
apparently now well established, though differing so radically from the

“BE Od

5 hast Bais
‘(ft RSRl risers

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2

nahn aye

Fig. 8.—Hypoderma lineata: a, second stage of larva from back; b and c, enlargement of extremities;
d, ventral view of third stage with details of extremities at eand/,; g, dorsal view of mature larva with
enlargement of anal spiracles at h; i, the same, lateral view—natural size indicated by side lines (from
Insect Life).

views formerly held. The wandering habits of this larva are further
indicated by a number of well-authenticated cases of its occurrence
beneath the skin of the human subject. There it has usually exhib-
ited a similar wandering tendency, in one instance having covered a
distance of several yards before being removed. This particular
larva is represented in the accompanying illustration (fig. 10). Its
entrance into the human subject can be easily accounted for by sup-
posing it to be taken with milk.

In general appearance and size, the adult insect, roughly speaking,
is not unlike the common honeybee. It is about one-half an inch
long, the general color black, and is clothed with yellowish white
and reddish brown and black hairs. The margin of the head and
thorax and a band on the base of the abdomen are covered with long
whitish hairs. The upper surface of the head and thorax, and the
middle segments of the abdomen, together with the legs, are covered

8

with brownish-black hairs. There are four raised lines on the thorax,
which are polished and shining, as shown in the illustration (fig. 1).
The hairs on the tip of the body are reddish brown.

The European bot-fly (Hypoderma bovis) is a much larger insect,
and is strongly banded with yellow and black,
as indicated in fig. 2, the light areas repre-
senting the yellow color.

PREVENTIVES AND REMEDIES.

It is possible to greatly diminish the loss
Fig. 9.—Hypoderma bovis: a, occasioned by the ox bot, and this is notably

puparium, from side; b,same, true of the smaller herds belonging to the

from above, showing exit hole : c

of adult: c, cap which splits general farmer, dairyman, and to the raiser

off to allow theadult toissue— of improved breeds, which are better cared

natural size (after Clark). :

for and more easily handled. For the great

herds of half-wild cattle covering the extensive grazing districts of
the West and Southwest, any treatment becomes a matter of extreme
difficulty and will often be impracticable. Even in such cases, how-
ever, it may be possible to prevent excessive loss, as will be indicated
below.

The common means of preventing the attacks of this fly and of
killing the larvee after they have reached their final location in the
back are of very ancient origin, having
been referred to, in fact, by Pliny, writ-
ing in the first century of our era, and
were probably known much earlier.
Nothing better has been found for the
purpose in modern times, although the
methods are perhaps more effective
now on account of the better knowledge
of the habits of the insect.

The substances used are any strong
smelling oils and fats, by means of
which it is possible to prevent the fly
from depositing its eggs on the animal
and also to kill the larve in their final
stages in the back. The larve, during
their early and wandering stages, are! 116 :10>_Eerva,cprobebly ch

, * F 3 derma lineata, taken from boy: a,
out of reach, and it is impossible to ventral surface; b, anterior end; ¢,

kill them. anal end—all enlarged (from Insect
Life).

The oils commonly used for the pur-
poses mentioned are the train oils or fish oils, either alone or with
sulphur or carbolic acid mixed. The addition of the latter is espec-
ially favorable to the healing of sores and diseased places left by
the grubs. Common axle grease may be used for the same pur-

9

pose; also any other strong smelling grease or oil, with or without
the additions mentioned.

To protect the animals from the attacks of the fly, or in other words
to deter the fly from placing its eggs on them, it is necessary to smear
or spray the oil or grease on the legs, flanks, or other parts of the
animal most likely to be approached. The more pungent the sub-
stance used the better for the purpose. The applications will have
to be kept up during spring and early summer, and hence are very
difficult and expensive, and perhaps impracticable except in the case
of small herds of valuable cattle, dairy animals, and work cattle or
oxen. A correspondent writes that he has protected his work oxen
from the annoyance of this fly by keeping their heels smeared with
kerosene, applied by means of a rag tied to a long stick. He says:
“The steers soon learned the benefit and would allow me to apply the
oil without kicking.”’ In general, this treatment is probably out of
the question for range stock.

The application of oils is often recommended to kill the grubs in
the backs of animals, either smearing the substance liberally over the
infested region, or preferably applying it at the mouth of the breath-
ing hole of the grub, the location of which is indicated by a hard
swelling and a slight exudation of pus. The grubs are killed by the
closing with the oil of the pores through which they breathe and which
penetrate nearly to the end of the hole in the skin. One or two appli-
cations during the winter are said to be sufficient. The grubs may
be killed also by placing a small quantity of mercurial ointment in the
hole, or a few drops of spirits of turpentine, carbolic acid, or kerosene,
and further by piercing them with some sharp instrument.

There is one objection to this method of killing the grubs, viz, that
the dead grub remains beneath the skin of the animal and may cause
an abscess or suppuration by its subsequent decay. These methods
of treatment, however, have been long recommended both in this
country and Europe, and no bad results have been reported.

Wherever it is practicable, however, the grub should be entirely
removed, and this may be effected by applying pressure on either side
of the swelling indicating the presence of the grub, forcing the latter
out. Dr. D. E. Salmon reports that the grubs may be very success-
fully removed by means of small tweezers, applying a slight pressure
with the fingers to cause the grub to slightly protrude, then drawing
it fully out with the tweezers.

The benefit following the removal of the grubs is immediate, and
will repay considerable trouble in its accomplishment.

If by such winter treatment the majority of the larvee can be killed
or removed from the backs of the cattle, this in itself will furnish con-
siderable protection for range cattle if it be generally adopted. This

10

is, at least, about the only step which presents any practical possibili-
ties for the great grazing districts of the West and Southwest.

As a rule, the application of these remedies will necessitate means
of bringing the animals into close quarters in small pens, and is neces-
sarily attended with some expense and considerable labor.

C. L. Maruartt,
First Assistant Entomologist.

Approved:

JAMES WILSON,
Secretary.

WasuineoTon, D. C., July 19, 1897.

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