Mice and rats are a part of the rodent group, which includes squirrels, chipmunks, guinea pigs and more. While their are various rodent types, there is also several types of mice and rats. Typically mice and rats are distinguished by their size.
Norway rats and house mice now have many genetic, reproductive, developmental, morphological and anatomical differences. The list below is not exhaustive, but for those with a casual interest it should get you started:
• Genetic differnces: Norway rats have 22 chromosome pairs, house mice have 20 (see Levan 1991). Norway rats have 2.75 billion base pairs while mice have 2.6 billion (humans have 2.9). About 90% of rat genes have counterparts in the mouse and human genomes (Rat Genome Sequencing Consortium 2004). See Burt et al. 1999, Grutzner et al. 1999, and Watanabe et al. 1999 for more.
• Growth differences: In general, Norway rats develop more slowly than house mice. For example, Norway rat gestation is slightly longer (21-24 days) than house mouse gestation (19-20 days). Norway rats lactate for about 3 weeks, house mice for 2 weeks. Both species are born naked and blind, but Norway rats open their eyes at 6 days, they are fully furred at 15 days. House mice open their eyes at 3 days, have fur at 10 days (etc.).
• Anatomical differences: Norway rats have 6 pairs of nipples, house mice have 5 pairs.
• Morphological differences: Norway rats are larger, heavier and longer than house mice (Norway rat: 350-650 grams, 9-11 inch bodies and 7-9 inch tails; house mice: 30-90 grams, 3-4 inch bodies and 3-4 inch tails). Correlated with this larger size, Norway rat body parts are larger than those of the house mouse — rats have larger ears, feet etc. The heads of Norway rats are heavy, blunt and chunky, house mouse heads are small and sharply triangular with pointed muzzles. Note, however, that Norway rats have smaller ears relative to their heads than house mice.
• Sign differences: Due to their larger body size, rat feces are larger than mouse feces (also see differences in rat and mouse sign from a pest management perspective).
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Winter has come! Now is the time when our desire for indoor warmth increases. Rodents, squirrels and raccoons also like to sit by the fire and warm their hands! Call us today if you hear scurrying or scratching in your home.