Courtship and breeding principally occur in spring, although this activity may continue into summer, as documented by R. Conant in 1934, B.A. Kingsbury in 1996 and again with others in 2003. Males seek females, and may aggregate around them. Masses of snakes, known as mating balls, may be observed where the female remains relatively immobile, but alert, while multiple males endeavor to mate with her. This mating behavior is typical for natricine snakes. It is unknown whether copperbellies breed annually or less frequently, and we also lack significant information on clutch size. In 2004, J.W. Gibbons and M.E. Dorcas summarized litter size for N. erythrogaster as a whole, and reported that they ranged from two to 55, but averaged 17.7 across 53 records. Not enough data are currently available to state whether or not litter size is correlated with adult body size.

Little is known about survivorship. However, mortality during radiotelemetry studies suggests survival rates may be 70 to 80% per year for adults. Researchers from Purdue University - Fort Wayne noted that adult snakes that were tagged with passive integrated transponders, known as PIT tags, in 2001 were found in 2005. This indicates ages of at least 6 to 7 years.

Neonate, meaning newly born, copperbellies are quite small. Data is scarce for the National Park Service, but neonate plain-bellied water snakes sampled from a variety of locations average about 10 to 11 inches (250 to 270 millimeters) snout to vent length and 0.18 to 0.20 ounces (5 to 6 grams), as summarized by J.W. Gibbons and M.E. Dorcas in 2004. Observations of neonates in the fall are rare, and it appears that they may hibernate at—or at least near—their birthing site. Consequently, they are approximately the same size the following spring when they emerge.

Frogs and tadpoles are the copperbelly water snake’s main prey. This species hunts on land and in shallow water, and favors seasonal wetlands where frogs, toads and salamanders lay their eggs. In addition to large numbers of prey, the gradual drying of these wetlands provides excellent feeding conditions as tadpoles become stranded.

Copperbelly water snakes have a solid dark, usually black, back with a bright orange-red underside that is visible from a side view. The copperbelly water snake has fingers of dark pigment that extend onto the ventral scales that may meet, or nearly meet, at the belly. R. Conant documented additionally that this differs from the yellowbelly water snake that has dark, two-pigment that encroaches onto only the edge of the ventral scales. This observation was confirmed by multiple reaerchers across several decades, including additional research by R. Conant in 1949, S.A. Minton, Jr. in 1972 and R.A. Brandon and M.J. Blanford in 1995. The head and eyes of the copperbelly water snake are proportionally larger than those of similar species, as was documented by W.M. Clay in 1938, R. Conant in 1938 and 1951 and S.A. Minton, Jr. in 1972.

Measurements
Length: 3 to 5 ft

Copperbelly water snakes are generally in hibernacula, underground and inactive, from late October until late April, as documented by B.A. Kingsbury in 1996. U.S. Fish and Wildlife Service researchers noted in 1997 that although snakes in more southerly populations have been observed on the surface during winter warm spells, such activities seem to be limited and may be limited to injured or sick individuals.

Copperbellies stay nearby their hibernacula after first emerging and may re-enter the ground if the weather turns cold. Within a few days, however, they begin to move into adjacent wetlands. As the weather warms, copperbellies become more active, searching for food and also for mates. Courtship and mating occur largely in the spring. B.A. Kingsbury, and several other researchers, noted that individuals engage in what becomes the standard pattern of behavior. This includes spending a few days to weeks in one wetland, then moving upland or to another wetland. In the middle of the summer when air and water temperatures are relatively high, copperbellies are more crepuscular, although some will remain active during the day. They will also spend extended periods underground aestivating or in shallow water. By September, individuals are less active and begin exploring hibernation locations. By mid-October, most individuals are in hibernacula.

While copperbelly water snakes have both wetland and terrestrial habitat requirements, they are associated most often with wetland complexes that are characterized by a preponderance of shallow wetlands, many of which draw down seasonally. Thus, the species needs habitat complexes of isolated wetlands that are distributed in a forested upland matrix, floodplain wetlands that are fed by seasonal flooding - or a combination of both. Individuals move hundreds of meters or more between wetlands, and routinely use multiple wetlands during the course of an active season. They also spend substantial periods of time in upland situations, aestivating, which is a state of animal dormancy, foraging and shedding. In addition, fishless wetlands that have high anuran, meaning frog and toad, productivity, are required to provide habitat and a suitable prey base.