by Zoe Joy
Growing up, we learn that one of the key differences between mammals and reptiles is that reptiles generally lay eggs. However, this is not the case for the Red-sided Garter Snake. Interestingly, a female Red-sided Garter Snake will incubate her developing young within her abdomen before giving birth to live offspring.¹ When researching this intriguing fact online, it turns out that approximately 30% of snake species are known to give birth to live young rather than laying eggs. Female Red-sided Garter Snakes typically give birth to between 5 and 27 offspring, although litters of up to 50 young have been reported in Manitoba.²
Now let’s return to the beginning of their mating and breeding process. This article takes a deep dive into the breeding habits, seasonal schedule, pheromones, and mimicry of the Red-sided Garter Snake.
Red-sided Garter Snakes begin breeding in early spring, immediately after emerging from hibernation.¹ Snakes typically hibernate underground in large groups that can range from hundreds to thousands of individuals in a single location.¹ These communal overwintering sites are known as a hibernaculum (plural: hibernacula).¹ In northern Alberta, the Red-sided Garter Snake is considered a Species of Concern, and damaging or disturbing a snake hibernaculum is prohibited.¹ According to the Ontario Reptile and Amphibian Atlas, this species is the northernmost reptile found in Canada and is remarkably well adapted to cold climates, even surviving short periods of partial freezing.² In some northern regions, female snakes only reproduce every other year, or even less frequently.¹
The Red-sided Garter Snake is easily recognized by the three parallel yellow stripes running along its body, accompanied by its namesake red markings, which can appear as either red blocks or stripes.² These distinctive red markings are unique to this subspecies, while eastern garter snake subspecies tend to appear more brown in colour.² Female Red-sided Garter Snakes are also noticeably larger than males.¹
After emerging from their hibernacula, Red-sided Garter Snakes communicate by collecting scent particles with their tongues and transferring them to a specialized sensory structure known as the vomeronasal organ.¹ This subspecies is most commonly observed between April and mid-October.²
Once breeding begins, numerous males compete simultaneously to mate with a single female, typically near the hibernacula.² A “mating ball” is the term used to describe dozens of male snakes tightly surrounding a single female during courtship.³ These mating balls can contain up to 100 snakes at one time.³ Studies have shown that female Red-sided Garter Snakes actually become more attractive to males based on the number of males already courting them.³ In one study, significantly more males courted females already surrounded by multiple males than females that only had one or two males nearby.³
The Red-sided Garter Snake depends almost entirely on pheromones to enable males to locate and identify females.⁴ Males rapidly flick their tongues across the female’s body, allowing them to detect chemical cues that reveal the species, sex, population, season, reproductive condition, size, and even age of a potential mate.⁴
According to one scientific publication, some males, known as “she-males,” produce female-like skin pheromones and consequently attract courtship from other males.⁵ These “she-males” are individuals that have recently emerged from hibernation before regaining their full muscle strength and mobility.⁵
Along with the production of female-like pheromones, another alternative reproductive strategy observed in male Red-sided Garter Snakes is known as female mimicry.⁶ Female mimicry occurs when a male assumes female-like physical characteristics or behaviours.⁶ A small proportion of males release pheromones that attract other males as though they were females.⁶ Remarkably, studies have shown that these “she-males” are even more appealing to females than the average male. During competitive breeding events, “she-males” successfully mated with females significantly more often than typical males, demonstrating not only full reproductive capability but also a possible selective advantage associated with producing female-like pheromones.⁶ As these studies demonstrate, attraction within this species is influenced by a remarkable variety of behavioural and chemical factors.
Although the Red-sided Garter Snake is not currently considered an at-risk species globally, some researchers have suggested that populations may be vulnerable to significant declines following extreme weather events. This concern stems from the snakes’ tendency to congregate in exceptionally large numbers — from thousands sharing the same hibernaculum to hundreds participating in mating balls. Like the saying, “Birds of a feather flock together,” perhaps we can say the same for this remarkable snake subspecies:
“Snakes of a scale, take the same trail.”⁵
Bibliography
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Canadian Science Publishing. “Female Mimicry in Garter Snakes: Behavioural Tactics of ‘She-Males’ and the Males That Court Them.” Accessed July 7, 2026. https://cdnsciencepub.com/doi/abs/10.1139/z00-089?journalCode=cjz.
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NWT Species at Risk. “Red-sided Garter Snake.” Accessed July 7, 2026. https://www.nwtspeciesatrisk.ca/en/our-species-risk/red-sided-garter-snake.
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Ontario Nature. “Red-sided Gartersnake.” Accessed July 7, 2026. https://share.google/XxueC6zxhtQMA5UGv.
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Ontario Reptile and Amphibian Atlas. “Red-sided Gartersnake.” Pages 244–245. https://share.google/MOzpRq2was6KU2Dif.
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PubMed. “Female Mimicry in Garter Snakes.” Accessed July 7, 2026. https://pubmed.ncbi.nlm.nih.gov/4010782/.
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PubMed. “Social Dynamics of Group Courtship Behavior in Male Red-sided Garter Snakes (Thamnophis sirtalis parietalis).” Accessed July 7, 2026. https://share.google/EvNmbsVmbCKnkIhDD.
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Reptiles Magazine. “Scent and Snake Matings of the Red-sided Garter Snake.” Accessed July 7, 2026. https://reptilesmagazine.com/scent-and-snake-matings-of-the-red-sided-garter-snake/.
