Echinophthirius horridus

Geographic Range

Echinophthirius horridus is found in northern holarctic regions (Durden and Musser, 1994), i.e., in temperate, subarctic, and arctic coastal areas of the north Atlantic and Pacific Oceans, where its seal hosts may also be found (Grzimek, 1990). (Durden and Musser, 1994; Grzimek, 1990)


The immediate habitat of E. horridus may be described as the skin of its only known host, the true seal (Phoca vitulina). The more indirect habitat of this parasite is the habitat in which its seal hosts live. True seals, also known as harbor seals, bask and sleep on both rocky coastal ledges and sandy beaches which are uncovered at low tide. These seals stay near the shore in order to feed in the shallow coastal waters. (Grzimek, 1990)

Physical Description

Anoplurans, or sucking lice, resemble their chewing relatives in that they have small, wingless, flattened bodies. However, while chewing lice (order Mallophaga) retain mandibles for biting into their hosts, these structures are completely absent in Anopluran lice. Instead, Anoplurans have mouthparts that are highly modified for sucking the blood of their hosts. These mouthparts include four elongate stylets that form a fascicle, which pierces through the host's skin, withdraws blood, and conveys salivary material into the wound (Roberts and Janovy, 2000).

Anoplurans of the genus Echinophthirius have large fore-, mid-, and hindlegs, each equipped with a blunt claw that is used to grasp tightly to the skin and fur of their Pinniped hosts as they move about on land or in water (Kim et al., 1986). The head and thorax of these lice are thickly covered in hairs called setae and no eyes are present externally (Miller, 1971). Their abdomen is leathery with six pairs of small respiratory spiracles (Price and Graham, 1997). (Kim, et al., 1986; Miller, 1971; Price and Graham, July, 1997; Roberts and Janovy, 2000)


Like all Anopluran lice, the developmental stages of E. horridus include an egg, three nymphal instars, and an adult stage (Roberts and Janovy, 2000). The hatching of an egg is followed by a slow metamorphosis, during which the nymph becomes slightly more similar to an adult with each of the three moltings of its exoskeleton. This mode of development is termed hemimetabolous. (Roberts and Janovy, 2000)


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

Echinophthirius horridus reproduces only when its seal hosts are on land (Thompson, 1998). Eggs are fertilized when sperm from a male's pseudopenis is deposited into a female's genital opening; the female then glues the fertilized eggs to the fur of her seal host (Kim et al., 1986). (Kim, et al., 1986; Thompson, 1998)

Female lice provide nutrients for their eggs until they are laid; then they abandon them. (Roberts and Janovy, 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female


The lifespan of E. horridus is not known.


In the family Echinophthiriidae, to which E. horridus belongs, some of the body setae have become highly modified into flattened, overlapping scales (Grzimek, 1975). In some species, these setae help to trap an air bubble, or plastron, around the body of the louse through which the louse respirates (Marshall, 1981). However, E. horridus is not capable of this form of respiration. In the water, E. horridus stretches out its legs and cannot move (Messner, 1998).

The tendency for seals to form groups at traditional "haul-out" sites facilitates the transmission of E. horridus (Thompson, 1998). Studies of just how these lice spread have suggested contradictory methods. One study indicated that E. horridus was transmitted vertically from mother to pup while nursing, while another study suggested horizontal transmission (Thompson, 1998). It is evident in either case, however, that physical contact between seals while on land is necessary for the dispersal of E. horridus. (Grzimek, 1975; Marshall, 1981; Messner, July, 1998; Thompson, 1998)

Communication and Perception

Anopluran lice have short antennae bearing chemoreceptors and tactile hairs. They are also thought to have the ability to detect chemicals in the host's bloodstream that let them know when they have hit a blood vessel.

No information is available on how these lice communicate with one another. (Roberts and Janovy, 2000)

Food Habits

Echinophthirius horridus feeds exclusively on the blood of true seals (Phoca vitulina) during all stages of development (Geraci et al., 1981). Echinophthirius horridus uses the blunt claws on the ends of its legs to grasp tightly onto the seal while feeding. The louse uses its sucking fascicle to pierce through the skin of the seal directly into a blood vessel from which it withdraws blood. This mode of feeding by the direct insertion of mouthparts into a blood vessel is termed solenophagy (Greek for pipe + eating). A two-chambered pump located within the louse's head acts as a suction, while salivary anticoagulants keep the blood flowing smoothly (Roberts and Janovy, 2000). (Geraci, et al., 1981; Roberts and Janovy, 2000)

  • Animal Foods
  • blood

Ecosystem Roles

Echinophthirius horridus is an obligate ectoparasite of true seals. There are two important ways in which E. horridus affects its seal hosts. First, high burdens of these ectoparasites may compromise the seal's diving ability and thus its ability to successfully capture prey (Thompson, 1998). This can become even more serious if a nursing mother seal cannot catch enough food to ensure a healthy milk supply for her pup. In addition, E. horridus has been found to be an intermediate host of the seal heartworm, Dipetalonema spirocauda, which can be fatal (Geraci, 1981; Lunneryd, 1992). It is not known if either of these effects of E. horridus on its host are serious enough to cause a significant decrease in seal populations, but the threat is present. (Geraci, et al., 1981; Lunneryd, 1992; Thompson, 1998)

Species Used as Host

Economic Importance for Humans: Negative

This parasite has no known impact on humans.


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

Julie Ritter (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.


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


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


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


union of egg and spermatozoan


a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

internal fertilization

fertilization takes place within the female's body


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


the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.


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


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).


Durden, L., G. Musser. 1994. The sucking lice of the world: A taxonomic checklist with records of mammalian hosts and geographical distributions. Bulletin of the American Museum of Natural History, 218: 90.

Geraci, J., D. St. Aubin, B. Hicks. 1981. The seal louse, Echinophthirius horridus: An intermediate host of the seal heartworm, Dipetalonema spirocauda (Nematoda). Canadian Journal of Zoology, 59 (7): 1457-1459.

Grzimek, B. 1975. Animal Life Encyclopedia, Volume 2: Insects. New York: VanNostrand Reinhold Company.

Grzimek, B. 1990. Encyclopedia of Mammals, Volume 4. New York: McGraw-Hill Publishing Company.

Kim, K., H. Pratt, C. Stojanovich. 1986. The Sucking Lice of North America; An Illustrated Manual for Identification. University Park, PA: The Pennsylvania State University Press.

Lunneryd, S. 1992. Dipetalonema spirocauda and Corynosoma strumosum infection in harbour seal from the Kettegat-Skagerrak and the Baltic. Sarsia, 76 (4): 267-271.

Marshall, A. 1981. The Ecology of Ectoparasitic Insects. New York: Academic Press.

Messner, B. July, 1998. Is the sucking louse of seal capable of plastron respiration? The respiration of the sucking louse of seal Echinophthirius horridus . Drosera, 98 (1): 11-18.

Miller, F. 1971. Scanning electron microscopy of Echinophthirius horridus, Antarctophthirus callorhini, and Proechinophthirius fluctus with emphasis on antennal structures. Journal of Parasitology, 57: 668-674.

Price, M., O. Graham. July, 1997. Chewing and sucking lice as parasites of mammals and birds. United States Department of Agriculture, Technical Bulletin, 1849: 113-119.

Roberts, L., J. Janovy. 2000. Foundations of Parasitology; Sixth Edition. Boston: McGraw-Hill Higher Education.

Thompson, P. 1998. Prevalence and intensity of the ectoparasite Echinophthirius horridus on harbor seals (Phoca vitulina): Effects of host age and inter-annual variability in host food availability. Parasitology, 117 (4): 393-403.