Flies in Livestock
Dr. Mario Villarino, County Extension Agent for Agriculture and Natural Resources.
As temperatures start to warm up, pest populations take advantage from the weather and recent rain to increase populations. When referring to external pest populations, Drs Swiger and Tomberlin, extension entomologist indicated that
the most significant livestock pest in the United States is the stable fly. Its painful bite and blood-feeding stresses cattle and causes them to
injure themselves trying to escape attack. The harm to animal health is
especially noticeable when fly populations reach more than 20 per
animal, and can significantly lower income for livestock producers.
Research shows that heavy infestations of stable flies on beef
cattle have reduced weight gain by 25 percent and, in dairy cattle, have
decreased milk production by 10 to 20 percent.
To effectively and economically suppress stable flies:
• Identify them properly.
• Understand the insect’s life cycle.
• Use a combination of control strategies.
The stable fly, Stomoxys calcitrans, looks like the house fly and horn fly,
but it is considerably larger (1/4 inch). Unlike these flies, stable fly mouthparts
resemble a bayonet that protrudes from its head. It differs from the house fly in that it depends on blood as food and its bite is
extremely painful. And, while the stable fly also resembles the deer fly
and horse fly, it primarily attacks the legs of livestock. When attacked by stable flies, animals will stomp and kick their legs, making dairy cows difficult to
milk. Unrestrained animals will typically bunch together when
attacked, increasing heat stress.To efficiently suppress stable fly populations,
use an integrated pest management (IPM) approach of cultural, biological, and chemical tactics. Cultural control methods involve manipulating the environment to reduce insect pest populations. Sanitation is the most economical and effective method for suppressing stable fly populations.
In confined animal facilities:
• Eliminate stable fly breeding sites.
• Remove and spread decomposing
vegetation or bedding material that has
become mixed with urine and feces to allow
the material to dry faster and prevent
colonization by stable flies.
• Design the stalls to allow for complete
manure removal and drainage.
• Clean out the wet feed that remains in the
ends of troughs weekly.
• For small to moderate adult fly populations,
install sticky ribbons and other mechanical
traps when combined with sanitation.
However, sticky ribbons used alone will not
substantially reduce fly numbers. Change
them and other mechanical traps every 1 to
2 weeks because the ribbons dry out, become
coated with dust, or become
“saturated” with flies.
• At range or pasture cattle-feeding sites,
spread decomposing vegetation such as hay
bales that provide supplemental feed during
the winter. These become ideal stable fly
breeding areas the following spring (Fig. 4).
Feeding hay in hay feeders reduces wasted
hay trampled into the soil, and periodically
moving the feeding site reduces the
accumulation of wasted hay, helps eliminate
breeding sites, and allows the location to
Biological control: This IPM tactic uses
natural predators (fire ants), parasites (such as the
wasp Spalangia sp.), or pathogens (Bacillus
thuringiensis) to suppress pests.
The parasitic wasp, available commercially,
lays an egg into the stable fly pupa. Then the
immature wasp feeds on the pupa, eventually
killing it. The wasp develops into an adult and
emerges from the pupa to start the cycle again.
Research has not determined whether
parasites can effectively reduce fly populations.
Wasps may supplement an integrated program
based on sanitation, but are unlikely to adequately
control many breeding sites. They are more likely
to be successful if used with waste and water
management and chemical control. If you use
both biological and chemical controls, apply with
limited sprays or other application techniques
that will not come in contact with breeding sites
and kill the parasites. Do not count on establishing
a population on your farm: Wasps must be
released each year, If a stable fly problem
persists, many compounds are available for
suppressing adult and larval populations. These
compounds include sprays, backrubs, pole-rubs,
misters, and premise products. For more information on control of external parasites please contact the Hopkins County Extension Office at 903-885-3443.