Alaria americana

Geographic Range

Alaria americana are most frequently found in temperate regions, predominantly in northern North America. (Fernandes, et al., 1976; Roberts, and Janovy, Jr., 2000)


The habitat of this organism is extremely diverse, as it occupies four different hosts throughout its lifetime. The species thrives in areas close to water, which is needed for several developmental stages to occur. Adult flukes may occupy a range of definitive hosts including wolves, coyotes, foxes, cattle, lynx, bobcats, martens, and skunks. (Fernandes, et al., 1976)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

The adult Alaria americana ranges from 2.5-4.0 mm in length. It is dorso-ventrally flattened with a long forebody containing a pair of anterior flaps ventrally. This species is monoecious, with male and female reproductive organs found within each individual consisting of an ovary and a single testis. Adult flukes have oral and ventral suckers to aid in absorption and digestion of nutrients, which eventually leave the body through a single posterior pore. The genital pore is located posteriorly on the mid-hind body. This species is additionally characterized by the presence of pointed processes flanking the oral sucker as well as a pharynx and bifurcate intestine. Also found within Alaria americana are the vitelline glands which function in yolk production. (Marshall, 1972; Roberts, and Janovy, Jr., 2000)

  • Range length
    2.5 to 4.0 mm
    0.10 to 0.16 in


These organisms may require up to four hosts to complete one cycle. Adult flukes, residing in the intestines of the definitive canid hosts, pass unembryonated eggs through the feces of the host. After two weeks, these eggs hatch in water, releasing the miracidium. The miracidia locate species of planorbid snails as the next host and once inside, develop into a sporocyst. After nearly a year of maturation, daughter sporocysts release cercariae, which exit the snail and swim to the water surface. The cercariae then locate a tadpole, inside of which they develop into the mesocercaria stage. The mesocercariae may then be ingested by the definitive host, but more frequently pass on to a water snake, where they develop into diplostomula. The definitive host then ingests the water snake, and the diplostomula migrate to the small intestine. Here, they mature into adult flukes, thus completing the reproductive cycle. (Ax, 1996; Kearn, 1998; Roberts, and Janovy, Jr., 2000)


This species is monoecious, with male and female reproductive organs found within each individual consisting of an ovary and a single testis. Adult Alaria americana reproduce in the intestines of the definitive canid hosts, then pass unembryonated eggs through the feces.

There is no parental investment beyond release of the eggs.

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning


Because of the complexity of the life cycle and the number of transitions from one host to the next, this species must demonstrate high reproductive fecundity in order to survive. In addition, each developmental stage must be active and carry adaptations allowing it to successfully locate the next host and continue development. For example, miricidia are active swimmers with the ability to quickly penetrate a located intermediate host. Cercariae demonstrate a further adaptation: once released, they swim to the water surface and hang upside down. Here, a tadpole may swim by, and water currents will stimulate the cercariae to swim after this prospective host (Kearn, 1998; Roberts, and Janovy, Jr., 2000)

Communication and Perception

Bristles and small spines probably act as tactile receptors, and these animals also may have reduced chemoreceptors. (Brusca and Brusca, 2003)

Food Habits

Adult Alaria americana are endoparasitic and are located in the small intestine of carnivorous mammals, specifically species of the family Canidae. In their developing stages, they may be found in several intermediate hosts including planorbid snails, tadpoles, and water snakes. Adult flukes lack a mouth for feeding as well as a digestive system. In order to receive nutrients, the ventral sucker is used for digestion and absorption of mucus and tissue from the wall of the host intestine. (Roberts, and Janovy, Jr., 2000)

  • Animal Foods
  • blood
  • body fluids

Ecosystem Roles

Alaria americana adults are found in the small intestine of its final definitive host, usually carnivorous mammals, specifically species of the family Canidae. In their developing stages, they may be found in several intermediate hosts including planorbid snails, tadpoles, and water snakes.

Species Used as Host

Economic Importance for Humans: Negative

Mature worms of this species are typically highly pathogenic and often cause severe enteritis, killing the definitive host. The worm does not frequently infect humans, due to infrequent contact with tadpoles or water snakes that carry the infective mesocercariae. However, human infection has been demonstrated in a few cases, likely to be caused by ingestion of inadequately cooked frog legs. (Fernandes, et al., 1976; Freeman, et al., 1976; Roberts, and Janovy, Jr., 2000)

Conservation Status


Renee Sherman Mulcrone (editor).

Jennifer Koepsell (author), University of Michigan-Ann Arbor, Solomon David (editor), University of Michigan-Ann Arbor.



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.

World Map


living in landscapes dominated by human agriculture.

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 disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

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.


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


marshes are wetland areas often dominated by grasses and reeds.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


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


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.


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.


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


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.


Ax, P. 1996. Multicellular Animals: A new Approach to the Phylogenetic Order in Nature. New York: Springer Publishing.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Fernandes, B., J. Cooper, J. Cullen, R. Freeman, A. Ritchie. 1976. Systemic infection with Alaria americana (Trematoda). Canadian Medical Association Journal, 115: 1111-1114.

Freeman, R., P. Stuart, J. Cullen, A. Ritchie, A. Mildon. 1976. Fatal human Infection with Mesocercariae of the trematode Alaria americana . The American Journal of Tropical Medicine and Hygiene, 25(6): 803-807.

Kearn, G. 1998. Parasitism and the Platyhelminthes. New York: Chapman and Hall.

Marshall, A. 1972. Textbook of Zoology: Invertebrates. New York: American Elsevier Publishing Company, Inc..

Roberts,, L., J. Janovy, Jr.. 2000. Foundations of Parasitology (sixth edition). New York: McGraw Hill Publishers.