The red-sided garter snake (Thamnophis sirtalis parietalis) is a subspecies of the common garter snake, in the subfamily Natricinae of the family Colubridae. This slender subspecies of natricine snake is indigenous to North America and is one of the recognized subspecies of Thamnophis sirtalis. This subspecies is widely spread across northern United States and southern Canada.
Appearance
The red-sided garter snakes have an upper row of well-defined red spots, and lower row with patches of red color that smear on the dark area on either side of their back. These snakes have multiple yellow stripes present on their body. Thamnophis sirtalis parietalis is sexually dimorphic, where females are usually larger than males. The females can range from 18 to 24 inches in length, whereas males can grow up to 12 to 18 inches. The snakes of this subspecies are mainly non-venomous.
Phenology and habitat use
Winter temperatures near their habitat are very harsh and sometimes even drop below zero. During low temperatures in fall and winter, tens of thousands of male and female red-sided garter snakes hibernate together, in a shared underground communal den, for about eight months each year to protect themselves from cold weather and predators. When the temperature rises around 25 °C, it leads to the emergence of these snakes from their dens and triggers mating behavior. Since food or water is not available close to dens, the snakes migrate to feeding grounds after mating. In summer, the snakes move to mossy or marshy areas where they look for food. Adult snakes feed only for 2 to 3 months during summer, whereas the young ones feed till the start of winter. The adult primarily feed on ranid and wood frogs, and occasionally on mice and voles. The young snakes mostly feed on earthworms. Soon after feeding, close to the end of summer, the adult snakes return to their dens for winter hibernation. The young snakes, around one-year-old, spend more time in marshy areas to find food before the winter temperatures arrive and hibernate there as their small size makes them unnoticeable to predators. During hibernation, the energy stored from summer feeding is used for body growth and maintenance to survive in subzero temperatures for months.
Reproduction
In red-sided garter snakes, the breeding season usually begins in early spring and lasts for about a month. These snakes exhibit a polygynous mating system, which means that males mate with multiple females each season. During the mating season, male snakes form a mating ball near the dens and court females as they emerge. Each female is courted by hundreds of males upon emergence. After mating, males and females move to mossy summer grounds where they find food and water and birth the offspring. These snakes are viviparous and can birth about 30 young ones in one mating season. Gestation period is about 3 to 4 months, and the young ones reach sexual maturity at 1.5 or 2 years of life. In this species, the offspring are usually born before the adults re-enter winter dormancy, and immediately after birth, adult male and female snakes migrate back to their dens and re-enter hibernation in early fall before the temperature falls.
The reproductive system of male snakes includes testicles, epididymis, vas deferens, hemipenes, and renal sex segment. Testes produce sperm that are transported by epididymis to the vas deferens, which then transfer the sperm to hemipenes. These snakes have a double penis with one testis supplying seminal fluid to each hemipenis. Hemipenes are saclike organs that facilitate sperm transfer to the female. During winter, the segment of the vas deferens is used for sperm storage. The function of the renal sex segment is to produce copulatory pheromones and the granules for formation of a copulatory plug. The female reproductive system consists of ovaries, an oviduct, and cloaca. The ovaries and oviducts are long due to the streamlined body of the snake. Multiple follicles (eggs) are present on the elongated ovaries. After mating, it takes up to 6 weeks for sperm to travel through the oviduct and reach the developing follicles in the ovaries.