By Meredith Swett Walker
If you’re desperate to discover a new species of louse, looking for one on a bird is a good start. Looking for lice on one of North America’s most secretive birds, the Swainson’s warbler (Limnothlypis swainsonii), is an even better bet. Researchers just discovered two new species of chewing lice on this little songbird, which spends its summers skulking through the thick undergrowth of southeastern U.S. forests.
The newly discovered species, Myrsidea bensoni, a skin louse, and Brueelia limnothlypiae, a feather louse, are described in the latest issue of the Journal of Medical Entomology. Michel P. Valim, of the Museu de Zoologia da USP in Brazil, and Bryan M. Reiley, of Arkansas State University and the Illinois Natural History Survey, discovered the lice while working on a larger study of the effects of flooding on Swainson’s warblers in Arkansas.
Currently about 4,000 species of avian lice have been formally described. That is a lot compared to the about 1,000 species of lice that have been found on mammals. One reason for this disparity is that birds are more diverse. There are about 10,000 species of birds in the world compared to about 5,400 species of mammals. Because most species of lice are at least somewhat host-specific, more species of hosts means more species of lice.
But it’s not just the number of bird species that leads to the diversity of avian lice. There are often more louse species found on a given bird species than there are on a given mammal species. Lice tend to specialize in specific types of hair or feathers. For instance, the hair on the human scalp has a different structure than our pubic hair. That’s why crab lice (Pthirus pubis), also known as pubic lice or crabs, are typically found in the pubic area, but head lice (Pediculus humanus capitis) only infest hair on the head. (My apologies if reading that sentence made you itch.)
While mammalian hair is certainly not uniform, the feathers on a bird’s body are more diverse. If you have ever gotten up close and personal with a bird, you can see that the small feathers on its head are very different in structure from the flight feathers of the wing or the fluffy feathers covering the back and belly. From a louse’s perspective, the body of a bird offers more diverse habitats than the body of a mammal. More types of feathers, or habitats, means more species of lice.
So far M. bensoni and B. limnothlypiae have only been found on Swainson’s warblers, but co-author Valim says that now that these species have been described, researchers may recognize them on other species of birds in the area. However it is possible that M. bensoni and B. limnothlypiae are found only on the Swainson’s warbler. Lice are obligate ectoparasites. They don’t travel fast or far from their host, and they don’t live long when separated from their host. According to Valim, the only times that lice typically move between individual birds is during copulation and when birds are in the same nest. Because different bird species rarely copulate with each other or share a nest, the transmission of lice between two different species may be infrequent, and each host species may function as a “distinct island,” said Valim.
Valim and Reiley named the feather louse, B. limnothlypiae, after its host (the Swainson’s warbler), and they named the skin louse, M. bensoni, after Dr. Thomas J. Benson, an ornithologist who has done important research on Swainson’s warblers and who served as Reiley’s graduate advisor. You can find the formal description of the new species, an identification key for lice in the genus Myrsidea, and a detailed description of the nymphal stages for this genus in Valim and Reiley’s paper: “The Chewing Lice (Insecta, Phthiraptera) Fauna of the Swainson’s Warbler, Limnothlypis swainsonii (Aves, Parulidae).”
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Meredith Swett Walker is a former avian endocrinologist who now studies the development and behavior of two juvenile humans in the high desert of western Colorado. When she is not handling her research subjects, she writes about science and nature. You can read her work on her blogs http://picahudsonia.com and https://citizenbiologist.com or follow her on Twitter at @mswettwalker.