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No. 4, SECOND SERIES.

Jnited States Department of Agriculture,

DIVISION OF ENTOMOLOGY.

THE ARMY WORM.

(Leucania unipuncta Haw.)

GENERAL APPEARANCE AND METHOD OF WORK.

In the months of May and June, and sometimes as late as July,

wheat, oats, and other small grains, corn, timothy,
blue grass, and other grasses, but seldom or never
clover, are occasionally overrun by multitudes of
naked striped caterpillars about an inch and a quar-
ter long and a quarter of an inch in diameter, when
full-grown, rather dark in appearance and closely re-
sembling Fig. 1. They usually travel in one direction
from one field to another, destroying the crop as they
go. They have a habit of climbing the seed stalks
and cutting off the heads of timothy grass and of the
small grains.

DISTRIBUTION.

The army worm seems to be an indigenous North
American insect, and on this continent is most
abundant in the United States east of the Rocky
Mountains. Isolated specimens have been found
in England and South America, and the moth has
been captured in India, Java, Australia, and New
Zealand. It is nowhere known as an especially
destructive species, however, outside of the United
States. The region in which it especially flourishes
extends from eastern fowa to Maine and from
northern Texas to northern Alabama. East of the
Blue Ridge Mountains its southerly range as an
injurious species extends only to northern North
Carolina. The moth is often captured outside
these limits and frequently in considerable num-
bers, but the caterpillar does not seem elsewhere
to be a factor in agriculture.

32363—No. 4—06

Fig. 1.—THE ARMY
Worm: Full-grown
larva; natural size.
(From Comstock.)

NATURAL HISTORY AND HABITS.

The adult insect is a brown moth with a white spot on the center of
each fore-wing, as indicated at Fig. 2. The eges are very minute and
white in color, round, and are laid in strings of from 2 or 3 to 15 or 20,
They are pushed by the ovipositor of the female moth down into the
inner. base of the terminal leaf sheaths of grasses or grains. (See also’
Fig. 2.) A strong effort is apparently made by the female moth to
conceal them. They are laid most abundantly in the thickest tufts of
erass Which customarily spring up in pastures over spots where cattle
have dropped. In the vicinity of old fodder stacks the grass usually
grows high, and this also is a favorite place for egg-laying. The moths
do not confine their egg-laying operations to such localities, however,
and the eggs have been found in old
cornstalks, thrust under the sheath, and
even under the bark of old cedar posts.

The eggs are hatched in from eight
to ten days and the young caterpillars
feed for a time in the fold of the leaf,
crowing rapidly, and finally consum-
ing entire leaves.

Under ordinary circumstances, and
when not present in great numbers,
the larve feed mainly at night and in

_ & damp cloudy weather, remaining hid-
: 2 PRAY cone eatin acer wij. den during sunshiny days. In this
eggs in natural position in agrassleai— respect they resemble in habits the
SUecap ap apey. eee ee closely allied cutworms. They reach
full growth in three or four weeks, burrow into the ground, and
transform to the brown pupe shown at Fig. 2. In this condition
they remain in the summer time on an average about two weeks,
when the moth again appears.

The number of generations each year varies with the climate and the
season. There are, in the more northern States, two or three genera-
tions, and perhaps six in the more southern States.

We have said above that the insect normally feeds by night and
hides by day, and to this habit is due the fact that, although the army
worm is present every year all through the region especially indicated
in a previous paragraph, it is only noticed when it becomes excessively
abundant, and this occurs usually only at intervals of several years.

With a favorable succession of seasons the insect multiplies in geo-
metrical ratio, and at last becomes so numerous as tonecessitate migra-
tion for food. It then travels and feeds during both day and night,
and it is then that the insect becomes very injurious and that reports
of great damage are heard.

The insect passes the winter normally, as do most of the related cut-
worms, in the half-grown caterpillar or larval condition. Inthe South

3

it also undoubtedly hibernates as a moth, and there is some evidence
that it may pass the winter occasionally, although exceptionally, in
the egg state.

The injurious brood may be the first, second, or third. The over-
wintered larve may occasionally be so abundant as to attract notice,
but in the majority of cases it is the offspring of these overwintered
individuals which cause alarm.

In general it may be said that the worms are more apt to make an
injurious appearance in a rainy spring or early summer following a
season of comparative drouth. The present season (1894) bears out
these conditions in the Eastern States, and as a matter of fact the
army worm has been more abundant in certain eastern sections than
it has been since 1888.

REMEDIES AND PREVENTIVE MEASURES.

There is never any demand upon this office for remedies for the
army worm until it is almost too late to do any immediate good.
There are certain old-time measures which may be adopted to protect
certain fields from advancing armies, like the plowing of a furrow with
its perpendicular side toward the field to be protected and the subse-
quent dragging of a log through the furrow to keep the earth friable
and kill the worms which have accumulated in the ditch, and another
is the sprinkling of a strip of pasture or field crop in advance of an
army with Paris green or London purple in solution. In fields which
the caterpillars have already entered there is little which can be done
for their destruction which does not also involve the destruction of the
crop. The fields may be sprinkled by means of a broadcast sprayer
with an arsenical solution, or they may be rolled with a heavy roller
where one is at hand and the ground is level, or a flock of sheep may be
sent in, which will resuit in crushing most of the worms by trampling.

In the great majority of cases, however, these latter measures are
unnecessary, for the reason that nature herself almost always takes a
hand in the reduction of the excessive numbers of the insect, either by
unfavorable weather conditions or by the excessive multiplication of
natural enemies and parasites, so that it is extremely rarely that we
hear of one army-worm outbreak immediately following another.

In general, therefore, it may be said that, as soon as the worms are
discovered to be exceptionally numerous in a given field (and, as a
matter of fact, they are at first almost invariably restricted to the
immediate neighborhood of some definitely limited, permanent breed-
ing place), all energies should be devoted to the protection of the sur-
rounding crops by the means mentioned above, and the destruction
of the worms in the fields first attacked may be safely left to the last.

There are many localities in which the army worm is never seen, or,
rather, is never known to be injurious, and these localities owe their
exemption undoubtedly to the unconscious use of preventive meas-

4

ures. Clean cultivation, rotation of crops, cleaning up fence corners,
close pasturage, the burning over of waste grass land in spring or fall
are all preventive measures of great value, since, where these methods
are in vogue, the army worm will never be able to get a migratory
start, or, in other words, it never becomes so abundant as to necessi-
tate migration.

Bearing in mind the fact that the insect breeds normally in rank
grass, such as is usually found along the edges of swamps (not in
swamps, for the insect must have comparatively dry earth in which to
pupate) or in accidentally overfertilized spots in pasture lands, and -
that it feeds normally only upon true grasses, the farmer who has
once suffered from army-worm attack may easily prevent its recur-
rence by winter burning or by rotation and clean cultivation.

In cases where the worms have already entered a valuable field of
wheat before the farmer has become aware of their presence, and too
late to render ditching of any avail, some little good may be accom-
plished if the majority of the worms are full grown, or nearly full
grown, by the old method of “dragging the rope.’’ Two men, each
having hold of the end of a long rope, are sent through the field and
the rope is dragged over the heads of the grain. The backward jerk
of the stalks jars the caterpillars to the ground, and they are unable to
ascend to the heads again for some little time. This is a laborious
process, however, and has to be repeated almost immediately. It is
only to be undertaken where the number of worms in a field is com-
paratively small and where these are, as before stated, full grown or
nearly full grown, since in this case they will stop feeding and enter the
ground in a day or two.

NATURAL ENEMIES.

There is almost no prominent injurious insect in whose economy
natural enemies play a more important part than the army worm. We
have said above that in the great majority of cases actual destructive
measures against army worms which have once taken full possession ~
of a grass field are hardly necessary. This is because of the fact that
generally not more than one worm out of a thousand escapes death
from parasitic or predaceous insects. Where the army worm follows
its normal habit and feeds only at night, remaining hidden during the
day under the surface of the ground at the base of some tuft of rank-
growing grass, It is protected from these natural enemies, but when the
migratory instinct drives it forth and perverts its normal habit, caus-
ing it to march unprotected during the day, the swift-breeding tachina
flies attack it at once, multiply most rapidly, and in connection with
its other parasites and with the predatory ground-beetles, reduce its
numbers once more to the noninjurious point. We have said this is
generally the case; there may be exceptions, but we have never seen
one. It is important, however, for the farmer to be able to recognize

5

the appearance of a parasitized worm, as in this way his confidence in
the future may be restored.

We show at Fig. 3 the head and front segments of an army worm
bearing eggs of the red-tailed tachina-fly (Nemorsea leucanix). The
eges are white, oval, less than one-sixteenth of an inch long, and are
glued fast to the skin of the caterpillar,
usually on the back of the front segments.

-From half a dozen to fifty or more of these
eggs may be attached to a single caterpillar,
and from each hatches a maggot which pene-
trates the body of the army worm and ulti-
mately destroys it, unless the caterpillar
should happen to cast its skin so soon after =}
the eggs are laid that they do not have time | pS RI ie cance eae
to hatch. The adult tachina-fly resembles ae et ioe a
a rather large house-fly, except that it has YrePartol Gear eeeeriaae

ared tip to its abdomen. Hundreds and ed, somewhat enlarged. (From

thousands of these flies are usually seen 9 SO" 10%”

buzzing about a field infested by the army worm, and their presence
should be welcome to the farmer.

The extent of the parasitism of the injurious brood of the army
worm may be indicated by two instances from our personal experience.
In 1880 we visited a large tract of land planted in timothy grass, in
the vicinity of Portsmouth, Va. A search for hours during the hot
part of the day failed to show a single worm which did not bear tachina
eggs. In 1882 we visited wheat fields in the vicinity of Huntsville,
Ala., which were then being overrun by this insect. Here, although a
number of worms were noticed which did not bear tachina eggs, they
were destroyed by ground-beetles to such an extent that when we
attempted to catch an adult moth a little later in the season by means
of trap lanterns and sugar, we were unable to secure a single specimen.
The entire army had been annihilated, and it is worthy of remark that
in neither of these localities has the army worm ever been seen since
in injurious numbers, although fourteen years have elapsed in the one
case and twelve in the other.

as

vi

L. O. Howarp,
Entomologist.
Approved:
J. STERLING Morton,
Secretary.
Wasuinerton, D. C., June 16, 1894.

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