External Parasites In Beef Cattle
External parasites are a nuisance and a dangerous threat to cattle in any part of the world.
These creatures can only live by feeding from the host animal and this ends up depleting the energy and nutrition
stores of the host. When external parasites exist in a herd of beef cattle, there are many problems that result
• Weight loss
• Decreased meat and milk production
• Generalized weaknesses
• Skin problems like mange and dermatitis
• Potential secondary infections through skin wounds
• Transmission of diseases from ill animals to healthy stock
External parasites that affect beef cattle include
• Cattle Grubs
Although the warmer months present the biggest problem for owners of beef cattle these external
parasites are a year round problem that must be dealt with properly.
Beef Cattle and Flies
Flies are a common insect that has one set of wings and there are almost two dozen types of flies
that affect beef cattle and other livestock. The main challenge that is presented with flies is that they do not
live on the animals and only have sporadic contact with a herd.
Blood Sucking Flies
• Blood Sucking Flies include the black flies that are small insects with a humped back and a
sturdy body. These external parasites are seen around the mucous membranes of the cattle including the eyes, ears,
nares, and mouth. The females are the feeders and they will draw blood during the daytime. The bites of these
insects are extremely irritating and can leave open sores. There have been animals that have died from anemia and
allergic reactions to the bite of black flies. These blood sucking parasites lay eggs on fallen logs, branches,
stones or other surfaces that are accessible in small eddies of streams.
• Horn Flies are another bloodsucker that can be troublesome to any beef cattle herd. These flies
are aggressive biters and they can quickly create festering, open sores on the underline or head of an animal. Horn
flies cluster when the bite and they show a preference to attack the withers and back of cattle. These parasites
can transmit many diseases within a herd, especially anaplasmosis. If the number of Horn Flies per herd animal is
50 or greater, it is a threat and should be addressed, but some numbers greater that 20,000 per animal have been
documented. This parasite lays eggs in extremely fresh manure that is less than 10 minutes old and the larvae hatch
in less than 24 hours. The average female Horn fly can lay about 200 eggs during her life and 10-14 days is all
that is needed for these insects to go from egg to adult. Horn Flies stay on their host animals continually and
feed up to 20 times during a 24-hour period.
• Horse and Deer Flies are strong flying insects that also feed during the daytime and they have a
notably vicious bite. These parasitic insects are responsible for much of the low weight gains and decreased milk
production among many beef cattle operations. The frequency and severity of the bites of these two types of flies
will often cause cattle to run or exhibit wild behavior. There are some herds that have been known to stampede due
to attacks by Horse or Deer Flies. These two insects are known as Tabanids and they have an anticoagulant that is
released into the host when they make the bite. This makes the animal ooze blood, which exposes them to bacterial
diseases and other parasitic infections. Some of the diseases that can be transmitted by these insects include
tularemia, anaplasmosis, and even anthrax. The eggs of these flies are laid in areas of vegetation and in other
moist environments. Horse and Deer Flies have varying life spans depending on the particular species, but some can
live as long as 2 years.
• Sand Flies are another blood-sucking parasite that affects beef cattle, particularly in the
southern states. In the Southeast, they are frequently called “No See Ums”. These creatures are more nuisance and
aggravation than serious threat, but they can cause suffocation if their numbers are large enough. A few species of
Sand Flies are also known to spread helminths and blue tongue virus among cattle herds.
• The Dog Fly (or Stable Fly) looks much like a house fly but it has a pronounced mouth made for
biting and both males and females will feast on livestock if they are not controlled. The bites from these external
parasites causes discomfort and blood loss. They are known to transmit both anaplasmosis and anthrax. Females can
lay up to 600 eggs during their lifetime and these insects mature in as little as 2 weeks. Their total life span is
21 to 58 days. If there are more than 10 of these flies per animal in a herd of cattle it can be crippling
Non-Blood Sucking External Parasites
• Cattle Grubs consist of two species in the US. There is the common cattle grub as well as the
Northern variety. At present, the common cattle grub is found only in the state of Florida and the Northern cattle
grub appears on those beef cattle living in other states. The common cattle grub lays eggs mostly on the hair of
the animals and can attach up to 15 eggs on just one hair. The eggs will hatch in 3-4 days and then the maggots
will tunnel into the skin of the animal. The common cattle grub larvae will move to the mucous membranes of the
gullet while the Northern variety will move into the spinal cord. During the fall months, these larvae will move to
the back of their host cattle and will eat a hole through to the outside so that they can breathe. When the larva
is ready to pupate, each will push through the skin and drop to the ground. Because of these larvae, the animal
experiences great discomfort and irritation. It suffers from fatigue and decreases in weight gain and milk
production. The open sores can also lead to infection and other illnesses. The animal carcass will also show the
infestation and any meat near the grubs will be foul and discolored leading to waste. Even the hide value is
decreased greatly because of the holes found in the animal skin.
• When Fly Maggots are present in the host animal’s tissue it is known as Myiasis. One of the most notorious of all
the maggots is the Primary Screwworm. This parasite only feeds on live tissue. The Southeast have been able to
eradicate the problem, but there is always a chance for it to return.
• Secondary Screwworms and Blow Flies also feed on the sores of animals and can infest any open wounds.
Lice are parasitic throughout their life stages. They are very species specific and lice that may
affect horses will not bother cattle, and vice versa. Some of the louse species will only suck nourishment from
their host animal, but there is a cattle biting louse that creates skin irritations and discomfort year round. Fall
to early spring are the times when lice population explodes and during the summer they tend to be a minimal problem
for beef cattle herds. Lice are transferred by contact and can cause animals to be nervous and irritable. Many lice
infected cattle will show weight loss, listlessness, and raw areas on their hide.
Mites have short life spans from 8 days to a month and most are barely able to be seen without the
aid of a microscope. One of these parasitic species is the Mange Mites that tunnel just under the hide of a host
animal. The tunnels will have dried, scabby nodules at the opening and the cattle will constantly rub and scratch
trying to relieve the discomfort. An infested host can develop wide spread infection and large scabs over the body.
It is imperative that all animals in the herd be treated to halt the attack from these contagious parasites.
Mosquitoes and Ticks
Mosquitoes and ticks are small insects but they can create a great deal of discomfort and pain in a
cattle herd. Both of these parasitic insects can be the reason for weight loss, decreased milk production, and
anemia in beef cattle. The bites from these animals also spread many diseases, and the bites can create sores that
lead to secondary infections.
With the many different types of external parasites that threaten beef cattle herds it is important
to be alert to any danger. Taking measures to prevent external parasites is the first step to a healthy herd. Even
the most stringent prevention can still fail to keep all of the parasitic threats at bay. Identifying the problem
early and handling the treatment quickly and appropriately is necessary for optimum cattle safety and health.