External structure and life cycle of lice

Classification & Distribution

  • incomplete development (egg, nymph, adult)


  • Closely related to Hemiptera and Psocoptera
  • The order is divided into four suborders (Ischnocera, Amblycera, Rhynchophthirina, and Anoplura) distinguishable from one another by the size of the head, the shape of the third antennal segment, and the presence or absence of maxillary palps.

Distribution: Common ectoparasites of birds and mammals.

Worldwide Number of Families Number of Species

Life History & Ecology

All Phthiraptera are wingless external parasites of birds and mammals. There is a continuing debate among entomologists regarding the ordinal grouping of these insects. “Splitters” divide them into biting lice (order Mallophaga) and sucking lice (order Anoplura). The distinction is based primarily on the presence or absence of mandibles that are suitable for biting and chewing. “Lumpers” include all parasitic lice in a single order (the Phthiraptera). As justification, they cite numerous similarities in structure and ecology.

The biting lice probably evolved first on birds, feeding on feathers and dead skin cells. But sometime during the Cretaceous period (less than 135 million years ago) biting lice expanded their host range to include certain groups of mammals. A few of these lice (suborder Rhynchophthirina) developed the habit of breaking their host’s skin and feeding on its blood. This lineage presumably gave rise to other sucking lice (suborder Anoplura), all of which are blood-feeding ectoparasites of placental mammals.

Unlike many other ectoparasites, the Phthiraptera cannot survive long if separated from the body of their host. Eggs (called nits) are glued directly to the hair or feathers and nymphs feed on the parental host. Since lice have no wings, dispersal to new host animals is limited to occasions when members of the host species come into direct contact with each other. This close interspecific association means most lice are limited to a very narrow host range — often only a single species.

Physical Features

  • Head broad, with mandibulate mouthparts
  • Antennae short; 3-5 segmented
  • Eyes reduced or absent
  • Tarsi 1- or 2-segmented, most species have two small claws
  • Head conical, with suctorial mouthparts
  • Antennae short, 3- to 5-segmented
  • Eyes reduced or absent
  • Tarsi usually 1-segmented with a single large claw

Economic Importance

Sucking lice are responsible for the spread of disease in humans and domestic animals. Pediculosis is an infestation of lice anywhere on the human body. It is usually characterized by skin irritation, allergic reactions, and a general feeling of malaise. In addition, the human body louse is responsible for the spread of relapsing fever (Borellia recurrentis), epidemic typhus (Rickettsia prowazeki), and trench fever (Rickettsia quintana). Lice associated with domestic animals have also been implicated in the transmission of disease (e.g., hog lice spread pox virus and cattle lice spread rickettsial anaplasmosis). Biting lice do not usually spread disease pathogens, but heavy infestations in poultry can cause severe skin irritation, weight loss, and reduced egg production.

Major Families

      • Philopteridae (Bird Lice) — a large family (500 species) containing several species that are pests of poultry.
      • Trichodectidae (Mammal Chewing Lice) — ectoparasites of mammals, including pests of domestic cattle and sheep (e.g., Bovicola bovis).
      • Menoponidae (Poultry Lice) — includes several important pests of poultry (e.g., Menopon gallinae and Menacanthus stramineus).
      • Haematopinidae (Ungulate Lice) — ectoparasites of cattle, deer, pigs, horses, and zebras (e.g., the hog louse, Haematopinus suis).
      • Pediculidae (Body Lice) — includes the human body louse (Pediculus humanus humanus) and the human head louse (P. humanus capitis).
      • Pthiridae (Pubic Lice) — includes Pthirus pubis, the human pubic (or crab) louse.
  • Louse-borne disease is particularly common in wartime when soldiers are forced to live in crowded and unsanitary conditions. Trench fever was especially widespread during World War I, and was probably a major factor in the final collapse of the Russian army.
  • Lice that feed exclusively on blood do not get a well-balanced diet. To compensate for the absence of certain vitamins and amino acids, these lice have intestinal symbionts (mostly bacteria) that provide additional nutrients.
  • A “nit” is the egg stage of a louse. Nits are always glued to the hair of the host animal. The term “nitpicking” refers to the type of detailed or meticulous efforts that would be needed to find and remove the nits from an animal’s fur.
  • Among the members of certain South American Indian tribes, it is customary to collect and eat the lice from one another’s body. They view this behavior as a way of sharing each other’s soul.
  • The suborder Rhynchophthirina includes only one genus and two species. One species is a parasite of Asian and African elephants; the other species is a parasite of African wart-hogs.
  • All members of the family Echinophthiriidae are ectoparasites of aquatic mammals (mostly seals and sea lions)


External structure and life cycle of lice

Biology of Pediculus

Figure 1: Pediculus humanus. Illustration by Sharon Belkin. Garcia 547. Figure 2: Phthirus pubis. Illustration by Sharon Belkin. Garcia 548. Figure 3: Louse egg (nit) on hair shaft. Photograph by Duane J. Gubler, CDC. Garcia 548.

Pediculosis is caused by organisms of the phylum Arthropoda, class Insecta, order Anoplura (blood-sucking lice) and genus Pediculus. The three species that commonly infest humans are Pediculus humanus capitus or head lice, Pediculus humanus humanus or body lice, and Phthirus pubis or pubic lice, also known as crabs.

Lice are visible to the naked eye, with P. humanus 2-4 mm long (see Figure 1) and P.pubis 1mm long (see Figure 2). The lice are flattened dorsoventrally, and are characterized by legs with claws adapted for clinging to hairs and fibers on the body of the host, as well as mouth parts used for piercing the skin of the host to attach to it to suck blood. Lice are wingless, so they can only be transmitted from host to host via direct contact. The eggs laid by the female louse are oval shaped (see Figure 3) and attached to the hair shaft of the host.

Life Cycle:
The adult louse attaches to the skin via its mouthparts and sucks blood from the host to feed itself. Female lice lay eggs at the base of the hair shaft for up to 30 days, though few live that long, and then die. In body lice and head lice, females can lay six to eight eggs per day, and the eggs take on average 7 days to hatch and then another 7 days to reach sexual maturity. If they do not hatch within 20 days the eggs die. Female pubic lice lay about five eggs per day. Egg hatching requires 8 days and then it takes another 8 days for the louse to reach maturity. Adult pubic lice live three weeks longer than body or head lice.
Therefore the incubation period for the infestation is highly variable, as adult lice may be noticed as early as five days after infestation or as late as three weeks later.

Transmission of Pediculosis can only occur through parasite transfer from host to host through direct body contact with lice or lice eggs (nits) on bodies, clothing or personal articles. P. pubis are transmitted through sexual contact or other contact with infested external genitalia. Lice are host specific, and can only survive on the host and briefly (up to one week) in the environment. Head and pubic lice deposit and cement nits onto the hair shaft on the scalp or pubic area, while the body louse deposits eggs primarily on the seams of clothing. Contact with these eggs can also spread the infestation.
Β•Reservoir: There is no reservoir for Pediculus other than humans because the lice are host-dependent (they cannot survive long in the environment) and host-specific (there are several types of animal lice as well but they do not typically affect humans).
Β•Vector: There is no vector for Pediculus because they are transmitted via direct contact. However, the body lice themselves are vectors of louse-borne relapsing fever (Borrelia recurrentis) and louse-borne typhus (Rickettsia prowazeki, R. quintana). Lice become infected when they feed off the blood of a person infected with either relapsing fever or typhus. The infected louse dislikes the intense heat of the fevered body, so leaves the infected person and movees to a new host, where it deposist the parasites on the body of the new hosts through fecal matter excreted as it feeds on the new host. This fecal matter is rubbed into the skin by scratching, and thus the B. recurrentis and Rickettsia parasites are able to enter the new host’s body and infect him.


Lice: What They Are and How to Control Them Animal Science Facts

Lice are a common group of ectoparasitic insects of goats. Generally goat lice are host specific and only attack goats and their close relatives, such as sheep. There are five species of goat louse that fall into two categories based on feeding habits. The sucking lice feed by piercing the skin with tiny needle like mouthparts to take blood directly from the capillaries. The chewing lice (also known as biting lice) have large robust mouthparts designed to scrape and abrade the skin and hair. Chewing lice consume tiny bits of skin, skin secretions and hair for food. The feeding habits and activity of these insects result in discomfort and irritation to the animal. Infested animals often cause structural damage to farm facilities by rubbing and scratching on fences and posts resulting in hair loss, skin damage, wounds and secondary infections. Parasites cause animals to have an unthrifty appearance, poor feed conversion, and reduced weight gains and milk production.

Louse life cycle: Both sucking and chewing lice undergo simple metamorphosis. Except for the egg (nit) each life stage resembles the adult in appearance. The female louse attaches an egg to the hair near the skin. The egg hatches in about 7-10 days. There are three nymphal stages each about 5-10 days in length, followed by the adult. Adult lice may live several weeks. Infestations are most severe in the winter months and when animals are under stress.

Sucking Lice

Two species of sucking louse infest goats in the United States.

The African blue louse: Linognathus africanus was originally described from Nigeria but has spread to the United States, Australia, Europe and Asia. The African blue louse measures about 2 mm in length and has a distinct bluish color indicative of sucking lice (Figure 1). The female louse attaches a single egg to one or more hairs. The latter results in a matted appearance of the hair coat. This species is unique in that it occasionally infests animals other than goats including cattle, deer, dogs and turkeys. Severe infestations may result in hair loss, anemia or death in some instances. Although L. africanus can infest any part of the body, closely examine the neck, base of the ears, poll, and jaw for infestations.

Goat sucking louse: Linognathus stenopsis is often misidentified because of its similar appearance to the African blue louse. The goat sucking louse is found in temperate regions worldwide. The complete life history has not been studied. Severe infestations result in dermatitis and anemia. Goat sucking lice may be found on the back and legs.

Figure 1. African blue louse, Linognathus africanus.

Rabinder Kumar and Jack Lloyd, University of Wyoming, Laramie

Figure 1. African blue louse, Linognathus africanus.

Rabinder Kumar and Jack Lloyd, University of Wyoming, Laramie

Chewing Lice

Three species of these straw colored chewing lice infest goats.

Goat biting louse: Bovicola caprae (Figure 2). Eggs are deposited on hairs close to the skin and hatch in 7-10 days. Nymphs may disperse about the body feeding on skin debris. The entire life cycle requires about 36 days. B. caprae are most often found on short haired goats. However, occasional infestations of Angora goats occur. B. caprae are most abundant in the winter months.

Angora goat biting louse: Bovicola limbatus is often mistaken for the goat biting louse. This species is found anywhere Angora goats are raised. In the United States, meat goats pastured with Angora goats will become infested. The female louse lives about 18 days, during which she deposits about 1 egg per day on a single hair. The egg to egg life cycle is approximately 32 days.

Hairy goat louse: Bovicola crassipes is a large (2.2 mm) yellow louse easily identified by the abundance of hairs on its body. The hairy goat louse prefers long haired goats and is found anywhere Angora goats are raised. Eggs are attached to 2-3 hairs resulting in a matted unsightly appearance of infested animals. The life cycle from egg to egg is approximately 36 days.

Figure 2. The goat biting louse, Bovicola caprae. Ventral view of female.

Price and Graham, 1997. Redrawn from Emerson and Price, 1975 BYU Sci. Bull. Bio. Series.

Figure 2. The goat biting louse, Bovicola caprae. Ventral view of female.

Price and Graham, 1997. Redrawn from Emerson and Price, 1975 BYU Sci. Bull. Bio. Series.

Louse infested animals may be recognized by their dull, matted hair coat or excessive scratching and grooming behavior. Weight loss may occur as a result of nervousness and improper nutrition and blood loss to sucking lice may lead to anemia or death.

Lice are obligate external parasites that spend their entire lives on the animal. Lice are generally transmitted from one animal to another by contact. Dislodged adult lice may survive a few days, long enough to acquire a new host. Lice populations vary seasonally, depending largely on the condition of the host. Most sucking and biting lice begin to increase in number during the fall and reach peak populations in late winter or early spring. Animals under stress will usually support larger louse populations than normally found. Control of lice infestations is needed whenever an animal scratches or rubs to excess.

Diagnosis is by physical examination of animals for crawling lice and eggs attached to the hairs, or of material collected by plucking or combing.

Satisfactory louse control requires two applications at 10- to 14-day intervals to remove young lice emerging from the protective egg case. Replacement animals should be quarantined and treated twice before being introduced to the herd.

Anthelmintics such as Ivermectin and Moxidectin are effective against sucking lice. Note: Ivermectin and Moxidectin products are not labeled for goats.

Registered products for both sucking and chewing lice are residual sprays or pour-on products. Several different products are available for louse control. Use pesticides according to label directions to avoid contamination of milk, meat or the environment.

Caution: Young kids are especially sensitive to over-dosing.

Insecticide Formulation % Active Ingredient Signal Word Pests
Atroban 11% EC Insecticide
Schering Plough
Emulsifiable Concentrate 11% Caution black flies, eye gnats, horn flies, horse flies, house flies, lice, mange mites, mosquitoes, scabies mites, sheep keds, stable flies, ticks
Catron IV
Aerosol 5% Caution deer flies, fleece worms, horn flies, horse flies, house flies, gnats, stable flies, ear ticks, screwworms
Durvet 10% Permethrin
Durvet, Inc.
Emulsifiable Concentrate 10% Caution face flies, horn flies, stable flies, mosquitoes, lice, mites, ticks
GardStar 40% EC
Emulsifiable Concentrate 40% Danger black flies, deer flies, eye gnats, horn flies, horse flies, house flies, lice, mange mites, mosquitoes, sheep keds, stable flies, ticks
Martins 10% Permethrin
Control Solutions, Inc.
Emulsifiable Concentrate 10% Caution face flies, horn flies, stable flies, mosquitoes, lice, mites, ticks
Zeta Cypermethrin
Python Dust
Dust 0.075% Caution horn flies, keds, lice, ticks

Safe Pesticide Use:

  1. Read the label before using any pesticide, pay attention to all warnings and precautions.
  2. Store all pesticides in their original containers, away from food, feed and water.
  3. Keep all pesticides out of the reach of children, pets and livestock.
  4. Apply pesticides only as directed by the label.
  5. Dispose of empty containers promptly and safely.


Kaufman, P. E., P. G Koehler and J. F. Butler. 2009. External parasites of sheep and goats. ENY-273. UF/IFAS Extension. Gainesville, FL.

Price, M. A. and O. H. Graham. 1997. Chewing and sucking lice as parasites of mammals and birds. USDA, ARS. Tech. Bull. 1849.


Causal Agent:

Pediculus humanus capitis, the head louse, is an insect of the order Psocodea and is an ectoparasite whose only host are humans. The louse feeds on blood several times daily and resides close to the scalp to maintain its body temperature.

Life Cycle:

The life cycle of the head louse has three stages: egg, nymph, and adult.

Eggs: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are la />. They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the scalp.

Nymphs: The egg hatches to release a nymph . The nit shell then becomes a more visible dull yellow and remains attached to the hair shaft. The nymph looks like an adult head louse, but is about the size of a pinhead. Nymphs mature after three molts (, ) and become adults about 7 days after hatching.

Adults: The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white . In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head. To live, adult lice need to feed on blood several times daily. Without blood meals, the louse will die within 1 to 2 days off the host.

Life cycle image and information courtesy of DPDx.


Animal Diversity Web

More Information

Additional Information

Haematopinus suis hog louse

Geographic Range

Haematopinus suis is found in all places in the world where domesticated and wild hogs live. It is commonly found on livestock swine in the United States. (Wooton-Saadi, et al., 1987)

Haematopinus suis lives on the surface of swine. It grips the hair with its claws, and moves through the pelage in a s >Haematopinus suis lives in all areas where swine are found and can survive in extremely cold conditions often associated with domesticated swine. (Wooton-Saadi, et al., 1987)

Physical Description

An adult Haematopinus suis is the largest of the sucking lice, order Anoplura , measuring a little over 0.5 centimeters from the tip of the head to the end of the abdomen. At the very anterior part of the head are short antennae with three segments and modified mouthparts. The Anoplura are distinguished as the ‘sucking lice’, because of their modified stylets for sucking up a blood meal, as opposed to the more primitive order known as the ‘chewing lice’ ( Mallophaga ). Haematopinus suis mouthparts are contained in a structure known as the labrum, which bear teeth at its apex. Within the labrum is a structure known as the haustellum, which supports the four retractable stylets (the fascicle). The fascicle moves into host tissue during feeding and retracts back into head at the end of the meal. Two stylets, supported by a structure within the labrum known as the maxilla, lock together and form the food channel. One stylet just anterior to the food channel, derived from a structure known as the hypopharanx, connects the salivary gland to the locale of feeding. The other stylet, derived from the labium, the anterior most end of the mouth parts, is flattened with a serrated tip, which gu >Haematopinus suis exhibits a loss of maxillary palps found on other lice.

The thorax section of H. suis is reduced and primarily functional for locomotion. There are three appendages on each s >H. suis has spiracles for respiratory gas exchange as well as sex organs for reproduction.

Male H. suis are slightly smaller than females and are characterized by the presence of an aedeagus or sperm transferring organ. (Roberts and Janovy, 1996; Walker, 1994)


Haematopinus suis is hemimetabolous, meaning it has a gradual metamorphosis, rather than a complete metamorphosis as in holometabolous insects. Haematopinus suis metamorphosis consists of 3 nymphal instars, all permanent parasites. From hatching out from the egg, it takes young lice about 10 days to complete the three nymphal instars and become adults. After the 10th day, mating begins. (Sloss, 1994; Smith, et al., 1982)


No information is available on the mating system of these lice.

After mating the female lays eggs called nits on the hog’s hair close to the skin. She lays 3 to 6 nits a day for about 25 days, an average of about 90 nits per lifetime. The nits have opercula, small holes for gas exchange. Most eggs hatch in 12 to 14 days, but it can take up to 20 depending on temperature conditions. These lice become sexually mature about 10 days after hatching. (Sloss, 1994; Smith, et al., 1982)

  • Key Reproductive Features
  • iteroparous
  • year-round breeding
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • fertilization
    • internal
  • oviparous
  • Breeding interval Females lay 3 to 6 eggs per day, for 25 days.
  • Breeding season These lice can breed year round, but are most active in winter.
  • Average eggs per season 90
  • Average age at sexual or reproductive maturity (female) 10 days
  • Average age at sexual or reproductive maturity (male) 10 days
  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female


Haematopinus suis is a permanent parasite; it spends its entire life cycle on the swine host. In fact, if it becomes dislodged from the host, it only lives an average of 2 or 3 days, remarkably less than the average 35 day lifespan in association with the host.

  • Average lifespan
    Status: wild 35 days

As a permanent parasite, Haematopinus suis leaves its host only to move to another host, and shows stringent host specificity, only infecting swine. Therefore, the most common movement of lice between hogs is through direct contact; this includes sexual contact, as well as being in close proximity, as is often common with domesticated pigs. However, lice and nits can survive off the host for short periods for dispersal. Often, in domesticated pigs, lice and their eggs are found in places such as in hay, troughs, and fence lines. Other animals and humans, through clothing, can be unknowing carriers of louse eggs, carrying louse infection from one stable to another, without becoming infected themselves.

Haematopinus suis infection is seen most often in the winter season. Lice, especially young nymphal instars, live in the warm inner fold of the hog’s ear. However, H. suis bites the skin surface anywhere on the pig and often migrates to the abdominal region. Haematopinus suis moves through hog hair, and only attaches to host skin through mouthparts while feeding. (Smith, et al., 1982)

Communication and Perception

The sensory organs found on the head of H. suis include two simple eyes (not compound) and short antennae with chemoreceptors and tactile receptors. It is believed that, when feeding, lice know they have found a blood vessel by stylet chemoreception of nucleotide bases, notably ADP and ATP, which are anti-coagulation factors found in high concentrations around penetrated blood vessels.

It is not known how these lice communicate with one another. (Roberts and Janovy, 1996)

Food Habits

Haematopinus suis feeds exclusively on the blood of the host and is termed solenophage because its mouthparts burrow into a blood vessel for feeding. Haematopinus suis demonstrates complete host specificity; i.e. its host is always swine. The modified mouthparts of Haematopinus suis cut into the hog’s skin where the stylets move into a blood vessel and extract blood. The teeth of the labrum cut the skin and hence anchor the louse in place, the stylets move into tissue while secreting salivary material to breakdown tissue and inhibit coagulation, and find a blood vessel (usually a venule). Once penetration has occurred, the blood is sucked up the food channel by a pump mechanism in the louse’s head, and enters the digestive tract, where enzymes hemolyze erythrocytes, keeping the blood in a liqu > (Roberts and Janovy, 1996)

Ecosystem Roles

The ecological interactions of Haematopinus suis fall under the realm of parasitism, where one organism (the parasite) benefits to the detriment of another (the host). Haematopinus suis is an obligate ectoparasite of swine. It is also a vector (a mechanism which transports a parasite, often a disease causing parasite) of many lethal swine diseases. (Smith, et al., 1982; Wooton-Saadi, et al., 1987)

Economic Importance for Humans: Negative

It is estimated that economic losses from H. suis suffered by farmers in the United States range anywhere from 10 to 50 million dollars annually. This is a huge problem for hog farmers. Haematopinus suis infestation is not usually lethal to the swine population, but economic losses are attributed to decreased swine growth due to a decrease in food intake, skin irritation, and immune response to the parasite. In very young or sick pigs, death can occur from louse infection due to anemia. Furthermore, H. suis has been implicated as a vector of many swine diseases, such as swine pox virus, Eperythrozoon suis , and hog cholera, with lethal consequences. One reason H. suis is of such economic concern is because of its dispersal. Females lay large quantities of eggs, and movement from one hog to another is rap > (Smith, et al., 1982; Wooton-Saadi, et al., 1987)

Conservation Status

Haematopinus suis is not an endangered species. In fact, great measures are taken to eradicate H. suis in domesticated swine, due to the harm it causes its host population, and the economic impact on human consumption.

  • IUCN Red List [Link] Not Evaluated

Other Comments

Symptoms of H. suis infection in domesticated swine include itching with the feet and/or against objects or each other, blue skin, skin lesions, and decreased weight and food intake. Large numbers of H. suis can often be seen in the ear, neck, and tail regions of the hog.

Control measures include bio-security (quarantine) and chemical pestic >H. suis infection. Chemical pestic > (Sloss, 1994; Smith, et al., 1982; Wooton-Saadi, et al., 1987)


Allison Poor (), University of Michigan-Ann Arbor.

Robert Vaidya (author), University of Michigan-Ann Arbor, Solomon David (editor), University of Michigan-Ann Arbor.

living in landscapes dominated by human agriculture.

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

an animal that mainly eats meat

either directly causes, or indirectly transmits, a disease to a domestic animal

uses smells or other chemicals to communicate

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

union of egg and spermatozoan

fertilization takes place within the female’s body

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

A large change in the shape or structure of an animal that happens as the animal grows. In insects, “incomplete metamorphosis” is when young animals are similar to adults and change gradually into the adult form, and “complete metamorphosis” is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

having the capacity to move from one place to another.

reproduction in which eggs are released by the female; development of offspring occurs outside the mother’s body.

an organism that obtains nutrients from other organisms in a harmful way that doesn’t cause immediate death

an animal that mainly eats blood

reproduction that includes combining the genetic contribution of two individuals, a male and a female

uses touch to communicate

uses sight to communicate

breeding takes place throughout the year


Roberts, L., J. Janovy. 1996. Foundations on Parasitology Sixth Edition . Boston: McGraw-Hill Higher Education.

Sloss, 1994. Veterinary Clinical Parasitology . Ames: Iowa University Press.

Smith, , Nettles, Dav >Journal of the American Veterinary Medical Association , 181(11): 1281-1284.

Walker, 1994. The Arthropods of humans and domestic animals: a guide to preliminary identification. . London: Chapman & Hill.

Wooton-Saadi, , Towell-Vail, Williams, Gaafar. 1987. Inc >Journal of Economic Entomology , 80 (5): 1031-1034.

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