Under Construction May 2011


Ondatra zibethicus


Length: 30mm (Adorjan and Kolenosky 1969), 24-43mm (Moore et al 1974), up to 45mm (Tumlison 1983), 10-120 mm (ASM#1), 20-40 mm (ASM #2), 25-35mm (ASM #3)  

Diameter Range: 70-107mm (Moore et al 1974), max 110 microns on the shield (Hicks 1977), 122 microns max, 102 microns ave (Tumlison 1983), 50-120 microns (Furskin 2006), 75-92.5 (ASM #1)

Medullary Index: 0.62- 0.66 ( ASM #1, 3)

Medulla:50 microns, continuous (ASM #1).The medulla in some areas has wide and flatted cells  that span the width of the medulla and are interconnected in an open lattice like arrangement. The medulla could be described as (bear with us) a poorly executed paper doll chain ( if the figures were mashed together). Further towards the tip of the hair the medulla changes to appearing as more of a honeycomb shape with three bubble-like perforations per the width of the medulla within the lattice-like structure. (ASM #1)  Medulla has big fingers of cortex poking into it giving the edge of the medulla a squiggly bumpy appearance.  The tip is more of a uniserial ladder (Teerink 1991)  Aggregations of three to five across in shield (Moore et al 1974).

Color: Brown-purple pigmentation occurring in clusters of dots throughout the cortex and the medulla.  Unbanded, but might be reddish brown near the tip and darker gray brown near base (Moore et al 1974).

Scales: Torn paper-like scales where each one is very undulose in overall shape giving the scales the appearance of having many points per scale. Looking a bit like a seismograph (ASM samples).  In the base scales very close together with a torn paper look.  Mid section the edges get smoother, scale are a little farther apart.  At the tip they are smooth edges and fairly irregular. (Teerink 1991)  Chevron type scales may be visible in the mid-shaft, but hairs might need to be rolled during casting to see it clearly ? (Moore et al 1974)


Length: 8-15 microns (Furskin 2006), 10-20mm (ASM #1), 15-20mm (ASM #2), 15-20mm (ASM #3)

Diameter Range: 12.5 microns (ASM #1,3)

Medullary Index: 0.4 ( ASM 1,3)

Medulla: Uniserial ladder (Furskin 2006). Discontinuous (Mathiak 1938)  5 microns wide, uniserial ladder with long bead-like cells that are taller than they are wide. (ASM)

Color: Seems to have a slight purplish or lavender cast with naked eye.

Scales: Stacked crowns

Macro Qualities: 19.3 – 24.3” long (Forsyth 1999). Naked, rat-like hairless tail distinguishes it from the beaver at first glance.  10-14” long with 8-11” tails.  Medium silvery brown in color to dark brown with a lighter belly (ADF&G 2008).  Fur is prime when the water is coldest in the early spring.  Females have darker pelts.  Good-to-fair “serviceability” (Bachrach 1953). Skin is 50-60 cm long (Furskin 2006).  In late fall or early winter, there may be two dark stripes on the animal. “Clear” fur will have no streaks. Mid winter and early spring are best pelts.  Spring furs may have teeth bites from fights. In comparison, “sheared” beaver will usually have the hair on the back leveled (cut) to the same length as the flanks.  “Unhairing” refers to the removal of the shining intermediate hairs in the fur industry. (Samet 1950)

Cultures: For example: Yup’ik men captured these small furbearers in the fall (p.245)  Fienup-Riordan (2007) Yuungnaqpiallerput: The Way We Genuinely Live.  Masterworks of Yup’ik Science and Survival.  Anchorage Museum Association.  Samet (1950) describes full skins being used as coat linings in the fur industry.  Reference to dying muskrat to look like fur seal in Fur News May 1916 p.10

Notes: ASM #1 is from the ASM education collection pelt ring, ASM #2 is from the ASM education collection pelt ring marked “natural”, ASM #3 is from a fur hat in the ASM educational collection, ASM #4 is from the Cargille Reference Set F-5 commercial furs

Troubleshooting:  Differs from mink because mink is elongated petal-shaped near the proximal (root) end and only becomes tile-shaped in the shield area.  Squirrels (Arctic Ground, Northern Flying and Red) have shorter guard hairs than the other rodents observed, with a length not exceeding 30mm except on the tail where it might reach 35mm on the arctic ground squirrel and 45 mm on the red squirrel.  Underfur of squirrels also may have a distinct brownish tip after a seemingly colorless shaft for most of its length.  Squirrels may also have intermediate sized hairs with long narrow interrupted or uniserial ladder medulla near the base until the shield where the medulla looks like tire tread.  To distinguish squirrel from muskrat, observe the underfur.  Often, muskrat underfur has a gray appearance to the naked eye with a hint of cool lavender purple.  Under magnification, the underfur often has no medulla, or a few fibers will have an interrupted medulla.  Arctic ground squirrel underfur has no medulla, either.  Squirrel is often banded.

Range: All of Alaska except the North Slope (Forsyth 1999). Mainland except some islands of southeast Alaska, the Alaska Peninsula west of the Ugashik Lakes, and the arctic slope north of the Brooks Range. 

Names: Order Rodentia (the rodents)  Rat musque, musquash (Bachrach 1953) In some places in the Eastern united States, “marsh rabbit” is a term used for muskrat, especially when seen on a menu.  However, marsh rabbit is in fact a different animal, a kind of cottontail rabbit.  Samet (1950) gives alternate names: Hudson seal, silvertone rat, Jersey rat, Northern rat, Silver rat, Texas Top, striped mink-cat, Grotzen rat etc.  “Hudson seal” is muskrat with guard hairs removed and was popular in the 1920’s and 1930’s according to the fur industry.

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