As its name might suggest, the southern watersnake is a strong swimmer, spending about 60 percent of its time in water. This species has been recorded remaining submerged for up to an impressive 24 minutes (5).
In the more southerly parts of its range, the southern watersnake may be active year-round (2) (6), but in other areas it becomes inactive during cold winters (2) (5). From about December, spells of cold weather cause this species to retire to a warmer refuge for hibernation, typically under a pile of vegetation near water or in the burrows of other animals (5) (6).
The southern watersnake is known to be both diurnal and nocturnal, often being most active at night during the summer when the intense heat becomes intolerable (3) (5) (6). If disturbed, this species’ first reaction is to take refuge in water (2) (5), but if it cannot escape, the southern watersnake may flatten its head and body on the ground to appear larger and perhaps mimic the venomous cottonmouth (Agkistrodon piscivorus) (5). Should the threat persist, the southern watersnake may strike ferociously and repeatedly (5), and if picked up or stepped on will emit a foul-smelling musk from scent glands at the base of its tail to deter its attacker (2) (3) (5).
The southern watersnake feeds on amphibians and fish (2) (4) (5), including eels, minnows and pikes (2), as well as the occasional crayfish (2) (5). While fish tend to be the preferred prey throughout most of this species’ range (2) (4) (5), it has been discovered that frogs make up the majority of its diet in Florida (5). The non-venomous southern watersnake (8) is an active forager (5) (6), flushing its prey out of hiding by poking its head into piles of debris and aquatic vegetation before quickly pursuing its quarry and swallowing it whole (5). Interestingly, fish prey is usually eaten head-first, whereas frogs are consumed rear-first (6).
Little is known about reproduction in the southern watersnake, although male courtship aggregations have been observed in spring in shallow-water habitats, presumably to mate with receptive females (2) (6). It is thought that several males may attempt to mate with a single female (2).
The southern watersnake is a viviparous species, meaning that the female gives birth to live young which develop inside its body (7). The timing of both courtship and the birth of the young depends somewhat on the subspecies and geographic location, but this species is typically thought to mate in the spring (4) (5). Young southern watersnakes are usually born between July and October (2) (5), although the Florida banded watersnake (N. f. pictiventris) is thought to give birth between May and August (5). Litters of up to 57 young have been recorded in this species, but generally fewer are born, with an average of between 20 and 25 per litter (2) (5). There is no evidence to suggest that female southern watersnakes produce more than one litter per breeding season (2).