Hystrichopsylla schefferi
{{Short description|Species of flea}}
{{Speciesbox
| fossil_range =
| image =
| image_caption =
| genus = Hystrichopsylla
| species = schefferi
| synonyms =
Hystrichopsylla hubbardi Augustson 1953
Hystrichopsylla mammoth Chapin 1921
| range_map = Aplodontia rufa distribution map.png
| range_map_caption = Distribution of host species
}}
Hystrichopsylla schefferi, also known as the mountain beaver flea and giant mountain beaver flea, is a parasitic nearctic insect and a flea, belonging to the order Siphonaptera, the fleas. With an adult body length of as much as {{convert|0.5|in|mm}}, it is the largest living flea in the world, and is native to the American Northwest.{{cite news
| last = Yoon
| first =Carol Kaesuk
| title =The Great Giant Flea Hunt
| newspaper =New York Times
| location =New York
| pages =D1
| language =
| date =29 July 2014
| url =https://www.nytimes.com/2014/07/29/science/the-great-giant-flea-hunt.html?emc=edit_th_20140729&nl=todaysheadlines&nlid=15765156
| accessdate = 29 July 2014}} Though most members of the genus Hystrichopsylla are not strongly associated with any particular host animal and will parasitize insectivores and rodents generally,{{cite book|author1=Gunvor Brinck-Lindroth|author2=F.G.A.M. Smith|title=The Fleas (Siphonaptera) of Fennoscandia and Denmark|url=https://books.google.com/books?id=O9p-iFsdPuoC&pg=PA32|date=22 June 2007|publisher=Brill|isbn=978-90-04-15151-2|page=32}} H. schefferi is monoxenously associated with the mountain beaver with which its range is coterminous.{{cite book|author1=B.F. Eldridge|author2=J.D. Edman|author3=John Edman|title=Medical Entomology: A Textbook on Public Health and Veterinary Problems Caused by Arthropods|url=https://books.google.com/books?id=C7OxOqTKYS8C&pg=PA111|date=31 December 2003|publisher=Springer Science & Business Media|isbn=978-1-4020-1794-0|page=111}} The fleas of the family Hystrichopsyllidae, along with the family Pulicidae, are the oldest of fleas in evolutionary history.{{cite book|author=Boris R. Krasnov|title=Functional and Evolutionary Ecology of Fleas: A Model for Ecological Parasitology|url=https://books.google.com/books?id=tkvr8h8zxFwC&pg=PA33|date=8 May 2008|publisher=Cambridge University|isbn=978-1-139-47266-1|pages=33}} H. schefferi can be distinguished from the very similar and closely related species Hystrichopsylla gigas dippiei by the number of spines in the pronotal comb, as H. g. dippiei has 36 and H. schefferi has 46.{{cite book|author1=Henry Ellsworth Ewing|author2=Irving Fox|title=The Fleas of North America: Classification, Identification, and Geographic Distribution of These Injurious and Disease-spreading Insects|url=https://archive.org/details/fleasofnorthamer500ewin|year=1943|publisher=U.S. Department of Agriculture|page=[https://archive.org/details/fleasofnorthamer500ewin/page/89 89]}}