THE
HE ACUTE PAIN produced by the insertion of

the proboscis of the stablefly brings to any man a sudden realization that this biting insect is pointedly different from the housefly, or typhoid fly, even if until then his opinion had been that the two were identical.

At times this fly becomes excessively abundant and occasions heavy losses among nearly all classes of livestock. Year in and year out it is a source of great annoyance, especially to horses and cattle, and is an all-too-common and persistent pest.

The adult stablefly resembles the housefly, but is slightly broader and feeds principally on the blood of animals, which it draws with its long, piercing mouth parts. It breeds in accumulations of various kinds of vegetable matter and also in manure, especially when the latter is mixed with straw. When strawstacks become wet soon after threshing the flies breed in the fermenting straw, and it is these conditions that produce the severe outbreaks,

Spraying animals with repellents is not very satisfactory, but the numbers of stableflies can be kept down by caring properly for stable refuse and by stacking or otherwise disposing of the straw.

This bulletin is a revision of and supersedes Farmers' Bulletin 540, The Stable Fly.

Washington, D. C.

Issued April 1920; revised October 1939

II

THE STABLEFLY: HOW TO PREVENT ITS ANNOY.

ANCE AND ITS LOSSES TO LIVESTOCK

By F. C. BISHOPP, principal entomologist, Division of Insects Affecting Man and

Animals, Bureau of Entomology and Plant Quarantine

CONTENTS

Page

5

Page
A tormenting and injurious rest..

1 Development and habits.
The common names of the insect and how it may Agricultural practices in relaticn to fly abun-
be recognized

1 dance.
Distribution and abundance

2 | Natural control.
Character of injury and losses

2 Artificial control.
Summary of life history...

4

9
10
11

A TORMENTING AND INJURIOUS PEST
THE STABLEFLY, or stock fly, is one of the most important

sources of annoyance to livestock throughout the United States.
When present in small numbers it has no apparent injurious effect,
but on frequent occasions conditions arise which permit its develop-
ment in enormous numbers, and at such times the injury to all classes
of livestock becomes marked.

In addition to being a source of annoyance to domestic animals,
the stablefly, when present in large numbers, has a deleterious effect
upon them owing to the quantity of blood drawn, and animals not
infrequently are so reduced in vitality as to permit certain diseases
to become acute and cause their death. In Africa and other parts
of the world this fly is capable of transmitting certain serious mala-
dies of horses and camels. In our country it probably plays a part
in the dissemination of anthrax, and investigations indicate that the
disease of horses known as swamp fever or infectious anemia is carried
by it. Work thus far conducted indicates that the fly acts solely as a
mechanical carrier, passing these diseases directly from one animal to
another in biting:

In addition to its role as a livestock pest, the stablefly is important
as an annoyer of man, and there is some indication that it is con-
cerned, in part at least, with the transmission of certain diseases of
man, most notable of which is infantile paralysis.

THE COMMON NAMES OF THE INSECT AND HOW IT

MAY BE RECOGNIZED

“Stablefly” is not entirely satisfactory as a common name for this
pest, as it is frequently abundant in open fields and along roadways
and is not uncommonly encountered about the house. Nevertheless

1 Known scientifically as Stomoxys calcitrans (L.).

1

it is found about stables more frequently than anywhere else. In certain localities such names as “stablefly," "stock fly," "dog fly," "wild fly," "straw fly,” and “biting housefly" are applied to it.

As the last name suggests, this insect is frequently confused with the housefly. The common housefly is not capable of biting, its mouth parts being soft and broad on the tip. On the other hand, the stablefly has mouth parts well fitted for piercing the skin of animals and sucking blood. The presence of such biting mouth parts, therefore, distinguishes it at once from the housefly. The tip of the beak can be seen protruding from beneath the front of the head when the fly is at rest. (See figs. 4 and 5.) The insect is usually slightly larger than the housefly and more robust. It usually alights upon an animal with the head directly upward, while another insect sometimes confused with it, the horn fly, rests with its head downward, and the housefly may assume various positions and moves much more frequently. The horn fly is much smaller than the stablefly, the wings are widely spread at the tips, and it is usually present on cattle only, where it occurs in small swarms, moving from one part of the animal to another when disturbed.

DISTRIBUTION AND ABUNDANCE

The stablefly is very widely distributed throughout the world. In fact it seems to have followed man and his domestic animals to all quarters of the globe. It becomes more abundant, however, in the temperate regions, such as the United States and Argentina. In the United States it is found everywhere, but within the confines of this country its abundance varies considerably.

Serious annoyance to livestock is most common in the Central States from Texas to Canada, where grain is grown extensively. Reports indicate that it may be important occasionally in various other sections and is a more or less persistent pest in all irrigated regions.

From time to time exceedingly severe outbreaks of this insect occur. One of the worst of these took place in 1912. Injury in northern Texas and in Oklahoma during the late summer and early fall of that year was unprecedented. The pest was abnormally numerous throughout the entire grain belt, including the southern portions of central Canada. Since 1912 the insect has appeared in great numbers on several occasions, but these outbreaks have not been so widespread.

This fly appears not infrequently on warm days during the winter and early spring in the Southern States, but seldom does it become sufficiently abundant in any part of this country to cause annoyance before early summer. It nearly always increases in abundance and injury is most acute during August and September.

CHARACTER OF INJURY AND LOSSES

Practically all warm-blooded animals are attacked by the stablefly, but some domestic species are much freer from injury than others. This comparative freedom is due largely to protection afforded by the hair of the host or by some of its habits. Mules, horses, cattle, hogs,