The common mudpuppy (Necturus maculosus) is a species of salamander in the genus Necturus. They live an entirely aquatic lifestyle in parts of North America in lakes, rivers, and ponds. They go through paedomorphosis and retain their external gills. Because skin and lung respiration alone is not sufficient for gas exchange, mudpuppies must rely on external gills as their primary means of gas exchange. They are usually a rusty brown color and can grow to an average length of 13 in (330 mm). Mudpuppies are nocturnal creatures, and come out during the day only if the water in which they live is murky. Their diet consists of almost anything they can get in their mouths, including insects, mollusks, and earthworms (as well as other annelids). Once a female mudpuppy reaches sexual maturity at six years of age, she can lay an average of 60 eggs. In the wild, the average lifespan of a mudpuppy is 11 years. Mudpuppies are small and can be compared to the size of a lizard. Mudpuppies can be a rusty brown color with gray and black and usually have blackish-blue spots, but some albino adults have been reported in Arkansas. In clear, light water, their skin gets darker, likewise in darker water, their skin gets lighter in color. At sexual maturity, mudpuppies can be 20 cm (8 in) long and continue to grow to an average length of 33 cm (13 in), though specimens up to 43.5 cm (17.1 in) have been reported. Their external gills resemble ostrich plumes and their size depends on the oxygen levels present in the water. In stagnant water, mudpuppies have larger gills, whereas in running streams where oxygen is more prevalent, they have smaller gills. The distal portions of the gills are very filamentous and contain many capillaries. Mudpuppies also have small, flattened limbs which can be used for slowly walking on the bottoms of streams or ponds, or they can be flattened against the body during short swimming spurts. Necturus maculosus specimens live in streams, lakes, and ponds in the eastern part of North America. They appear in the southern section of Canada, as far south as Georgia, and from the Midwest United States to North Carolina. In the more northern sections, they are called mudpuppies, and in the southern portions, they are called waterdogs. The mudpuppy hides under cover such as rocks and logs during the day and becomes more active at night. However, in muddy waters, the mudpuppy may become active during the day.