Trichodectes canis

Geographic Range

Trichodectes canis is known to inhabit many regions worldwide and is able to tolerate varying extremes of temperature. It has been noted that T. canis is not a native species of Australia but was brought in with domesticated animals. In northern areas like Scandinavia, T. canis is believed to be a major ectoparasite of dogs because the climate is too cold to harbor the presence of other ectoparasites such as fleas or ticks. (Emerson and Price, 1985; Ewing, 1936; Schwartz, et al., 1983; Stanneck, et al., 2007)


Trichodectes canis is a permanent parasite; therefore all life stages of this parasite live on the host. It is most commonly found living on domestic dogs, but has also been found on other canine species in the wild including coyotes, gray wolves and golden jackals. A couple of studies also noted that T. canis is more prevalent in canid hosts that are extremely young or old, or those that are unhealthy. Trichodectes canis prefers to live on certain areas of the host such as the back, the head and the neck. (Bádr, et al., 2005; Pollmeier, et al., 2002; Schwartz, et al., 1983)

Physical Description

Trichodectes canis is a small, chewing louse species in which members are flat-bodied and do not have wings. Females are typically larger than males with body lengths ranging from 1.75 to 1.82 mm in females and 1.60 to 1.68 mm in males. However, T. canis specimens discovered on raccoon dogs differed in body length from those found on domestic dogs, which suggests that polymorphisms also exist between lice in different habitats. Females of the genus Trichodectes can also be characterized by a special organ that grows from underneath the end of the abdomen. When viewed from above, portions of this structure peak out from under the abdomen resembling two curved appendages occurring on either side of the genital region. Females use this appendage for two purposes: to help glue their eggs to hosts' hair and to grip the fur in order to stay on the host. Members of the genus Trichodectes typically have antennae with three segments. However, in the family Trichodectidae sexual dimorphism occurs in the antennae, often resulting in differences in the size or shape of the antennal segments. Species in the family Trichodectidae are also characterized by having a single claw at the end of each tarsus. As in all Ischnocerans, T. canis has a pair of mandibles but has lost the maxillary palps. In addition, Trichodectes species are known to have retained a pair of degenerate eyes. (Allaby, 2009; Bádr, et al., 2005; Durden, 2001; Ewing, 1936; Morse, 1903; Stanneck, et al., 2007)

  • Sexual Dimorphism
  • female larger
  • Range length
    1.60 to 1.82 mm
    0.06 to 0.07 in


After laying the eggs, called nits, the female glues them to individual hairs on the host. Nits typically take 5 to 8 days to hatch. In the genus Trichodectes, nits have a cover which the larva pushes open when leaving the egg. The life cycle of T. canis consists of three stages of nymphs which morphologically resemble the adults, except for being smaller in size. The third nymph then turns into a sexually mature adult. In general, lice in the order Phthiraptera molt after each nymphal stage to proceed to the next stage. The entire life cycle takes around 3 to 5 weeks and takes place completely on the host. (Durden, 2001; Morse, 1903; Pollmeier, et al., 2002; Stanneck, et al., 2007)


Currently, mating systems for this species are poorly understood. Mating may occur year-round, and the male, who is the smaller of the two sexes, initiates this process by moving underneath the female and lifting its genital region up towards the female.

In lice, mating occurs between adult males and females year-round. Triatoma dimidiata reaches the stage of the sexually mature adult at around 3 to 5 weeks. This species of louse tends to mate on the host. Sometime after mating occurs, the female will glue her eggs onto the hairs of the host. The young will hatch 5 to 8 days after being laid. (Durden, 2001; Pollmeier, et al., 2002; Stanneck, et al., 2007)

  • Breeding interval
    Exact breeding interval for Triatoma dimidiata is unknown.
  • Breeding season
    Triatoma dimidiata breeds year-round.
  • Range gestation period
    5 to 8 days
  • Range age at sexual or reproductive maturity (female)
    3 to 5 weeks
  • Range age at sexual or reproductive maturity (male)
    3 to 5 weeks

Trichodectes canis exhibits no parental involvement.

  • Parental Investment
  • no parental involvement


Generally, the life cycle of Trichodectes canis takes 3 to 5 weeks to complete. Longevity has not been determined, however males have been speculated to have shorter life-spans when compared to females. (González-Acuña, et al., 2007; Stanneck, et al., 2007)


Trichodectes canis is a permanent ectoparasite meaning that in general, it never leaves the host. However, there is a possibility that males might be more motile than females. This louse exhibits high host specificity towards canine species but once within the canine species, it is not very host-specific. These lice can build up large populations on suitable hosts such as hosts that are physically unhealthy or hosts that live in wilderness areas. Typically domestic canines do not carry massive populations of T. canis. Due to the fact that T. canis lives on its host for the duration of its life, it has developed several anti-grooming adaptations to help it do so. In the genus Trichodectes, modified legs, mandibles and abdominal appendages in females all play a role in helping the organism stay fixed on the host by allowing the louse to grip the host hairs. (Bádr, et al., 2005; González-Acuña, et al., 2007; Morse, 1903; Pollmeier, et al., 2002; Stanneck, et al., 2007)

Home Range

Exact home range for Trichodectes canis is unknown, but many individuals spend their entire lives on one host.

Communication and Perception

Like most species of lice, members of the family Trichodectidae have hair-like appendages that extend from the antennal segments. The lice use these structures for perception; they function to help lice sense their surroundings. A number of chewing lice also have chemoreceptors located on the antennae. (Cruz and Mateo, 1996; Slifer, 1976)

Food Habits

Trichodectes canis is parasitic on canid species. Although domestic dogs are the primary hosts, it has been noted as a parasite on a number of different species including: gray wolves, coyotes, golden jackals, Patagonian foxes, crab-eating foxes, Bengal foxes, civets, and raccoon dogs. Trichodectes canis survives off of these hosts by consuming bits of skin from the surface of the host, or fluids produced by the skin. The skin particles are collected through the use of modified mouthparts that are used to scrape the surface of the skin. Species in the genus Trichodectes also have mouthparts that allow them to bite host skin. (Bádr, et al., 2005; Morse, 1903; Pollmeier, et al., 2002; Stanneck, et al., 2007)

  • Animal Foods
  • mammals
  • body fluids


There are no known predators of Trichodectes canis although this species may sometimes be unintentionally swallowed by the host during grooming or by humans who come into contact with infected pet dogs. (Roberts, et al., 2009)

Ecosystem Roles

As an ectoparasite of canids, Trichodectes canis can make the host more prone to disease by causing stress to the animal. This stress occurs as a result of increased hair loss and by the presence of wounds on the surface of the skin. These physical manifestations occur during host grooming which increases in response to growing louse populations which increases the itching sensations caused by the lice feeding. These factors may cause problems for hosts that live in colder climates by weakening the host’s tolerance for the cold. In addition to the physical damage, T. canis can also serve as an intermediate host for Dipylidium caninum which is a tapeworm of dogs. (Allaby, 2009; Bádr, et al., 2005; Durden, 2001; Schwartz, et al., 1983; Stanneck, et al., 2007)

Species Used as Host
Commensal/Parasitic Species

Economic Importance for Humans: Positive

There are no known beneficial impacts of Trichodectes canis on humans.

Economic Importance for Humans: Negative

When present in high populations, Trichodectes canis can be the cause of many adverse effects in household dogs. These effects include extreme hair loss and multiple scratches or wounds on the surface of the host’s skin, which are a result of scratching by the host. The host reacts this way because of the discomfort caused by the feeding habits of T. canis. As a result, this parasite has an adverse effect on humans economically, forcing pet owners to spend money on various veterinary medications to help alleviate the discomfort. Trichodectes canis can also serve as an intermediate host for dog tapeworms. Humans, who come into contact with a dog infested with T. canis and mistakenly consume the louse, may also be infected with dog tapeworms. (Allaby, 2009; Pollmeier, et al., 2002; Roberts, et al., 2009; Schwartz, et al., 1983; Stanneck, et al., 2007)

Conservation Status

Currently there are no conservation concerns regarding Trichodectes canis. Many efforts are being made to reduce population numbers to reduce the spread of disease and discomfort inflicted on domestic dogs.

Other Comments

Trichodectes canis and another canine louse species Heterodoxus spiniger are not usually observed on the same host. The reason for this is that T. canis is competitively excluded by H. spiniger.


Rachana Murthy (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Rachelle Sterling (editor), Special Projects.



Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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living in the southern part of the New World. In other words, Central and South America.

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living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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bilateral symmetry

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

causes or carries domestic animal disease

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


uses smells or other chemicals to communicate


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


union of egg and spermatozoan


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

internal fertilization

fertilization takes place within the female's body


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


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


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.


remains in the same area


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


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


living in cities and large towns, landscapes dominated by human structures and activity.

year-round breeding

breeding takes place throughout the year


Allaby, M. 2009. Oxford Dictionary of Zoology. New York: Oxford University Press Inc..

Barker, S. 1994. Phylogeny and Classification, Origins, and Evolution of Host Associations of Lice. International Journal for Parasitology, 24/8: 1285-1291.

Bádr, V., P. Stefan, J. Preisler. 2005. Trichodectes canis (De Geer, 1778) (Phthiraptera, Ischnocera), a new ectoparasite of the raccoon dog (Nyctereutes procyonoides) in the Czech Republic. European Journal of Wildlife Research, 51/2: 133-135.

Cruz, M., M. Mateo. 2001. Structures of the Preantennal Region of Several Species of Damalinia (Phthiraptera: Trichodectidae). Journal of Medical Entomology, 38/6: 802-808.

Cruz, M., M. Mateo. 1996. Antennal sense organs of Phthiraptera (Insecta). Scanning electron microscopy of the ‘pit organs’ of several species ofBovicola. MICRON, 27/1: 11-15.

Durden, L. 2002. Arthropods of Public Health Significance in California. Sacramento, CA: Mosquito and Vector Control Association of California.

Durden, L. 2001. Parasitic Diseases of Wild Mammals. Iowa: Iowa State University Press.

Eads, R. 1948. Ectoparasites from a series of Texan coyotes. Journal of Mammology, 29: 268-271.

Emerson, K., R. Price. 1985. Coevolution of Parasitic Arthropods and Mammals. New York: John Wiley & Sons, Inc..

Ewing, H. 1936. The Taxonomy of the Mallophagan Family Trichodectidae, with Special Reference to the New World Fauna. The Journal of Parasitology, 22/3: 233-246.

González-Acuña, D., C. Briceño, A. Cicchino, S. Funk, J. Jiménez. 2007. First records of Trichodectes canis (Insecta: Phthiraptera: Trichodectidae) from Darwin’s fox, Pseudalopex fulvipes (Mammalia: Carnivora: Canidae). European Journal of Wildlife Research, 53/1: 76-79.

Hanssen, I., N. Mencke, H. Asskildt, D. Ewald-Hamm, H. Dorn. 1999. Field Study on the insecticidal efficacy of Advantage against natural infestation of dogs with lice. Parasitology Research, 85: 347-348.

Mech, L., R. Thiel, S. Fritts, W. Berg. 1985. Presence and Effects of the Dog Louse Trichodectes canis (Mallophaga, Trichodectidae) on Wolves and Coyotes from Minnesota and Wisconsin. American Midland Naturalist, 114/2: 404-405.

Morse, M. 1903. Synopses of North American Invertebrates. The American Naturalist, 37/441: 609-624.

Pollmeier, M., G. Pengo, P. Jeannin, M. Soll. 2002. Evaluation of the efficacy of fipronil formulations in the treatment and control of biting lice, Trichodectes canis (De Geer, 1778) on dogs. Veterinary Parasitology, 107: 127-136.

Reed, D., M. Hafner, S. Allen, M. Smith. 2000. Spatial partitioning of host habitat by chewing lice of the genera Geomydoecus and Thomomydoecus (Phthiraptera: Trichodectidae). Journal of Parasitology, 86/5: 951-955.

Reeves, W., L. Durden, W. Wrenn. 2004. Ectoparasitic chiggers (Acari: Trombiculidae, Leeuwenhoekiidae), lice (Phthiraptera), and Hemiptera (Cimicidae and Reduviidae) from South Carolina, U.S.A. Zootaxa, 647: 1-20.

Roberts, L., J. Janovy, G. Schmidt. 2009. Foundations of Parasitology. New York: McGraw-Hill.

Schwartz, C., R. Stephenson, N. Wilson. 1983. Trichodectes canis on the Gray Wolf and Coyote on Kenai Peninsula, Alaska. Journal of Wildlife Diseases, 19/4: 372-373.

Slifer, E. 1976. Sense Organs on the Antennal Flagellum of a Bird Louse (Mallophaga). Journal of the New York Entomological Society, 84/3: 159-165.

Stanneck, D., J. Doyle, J. Ketzis, J. Heine, M. Fisher. 2007. Efficacy of Imidacloprid 10% and Imidacloprid 10% plus Moxidectin 2.5% against Natural Lice (Trichodectes canis) Infestations in Dogs. Parasitology Research, 101: S13-S18.