Northwestern Gartersnake
Thamnophis ordinoides
Northwestern Gartersnake
Thamnophis ordinoides
The Northwestern Gartersnake is the smallest Gartersnake in British Columbia, ranging in size from 35 – 75 cm, although most individuals tend to be less than 60 cm. Males are typically smaller than females, as increases with body size for females. The colour of Northwestern Gartersnakes varies more than any other snake species in British Columbia and melanistic and albino populations are more common than in other species. Most individuals are a dull brown-grey to olive, often with faint checkering on the dorsal surface and dorsal stripe. The colour of the dorsal stripe is incredibly variable and may be bright yellow, red, tan, blue, white, or cream. The width of the stripe is also highly variable, and some individuals will not possess a stripe at all. The belly is typically pale, and some individuals will have bold red or black markings. The scales of the dorsal surface are highly keeled, like all Gartersnakes in British Columbia. There is one characteristic that can help reliably identify a Northwestern Gartersnake: a pale upper lip with 7 upper scales.
Listen to the Indigenous words for “gartersnake” here!
The Northwestern Gartersnake may be easily confused with the Common Gartersnake and the Western Terrestrial Gartersnake. The Common Gartersnake is generally much larger, more likely to be black in background colour, and will often have red barring on the sides between the and stripes. The Western Terrestrial Gartersnake typically has 8 scales on the upper lip, two of them enlarged, and black spots that overlap with the dorsal stripe.
Northwestern Gartersnake
Common Gartersnake
Western Terrestrial Gartersnake
The Northwestern Gartersnake has the smallest distribution of the three Gartersnake species in British Columbia, occurring from southwestern British Columbia to western Washington, Oregon, and California. Within British Columbia, Northwestern Gartersnakes are found on Vancouver Island and most of the Gulf Islands, the Lower Mainland, and inland to Manning Park. The largest populations tend to occur in the immediate coastal areas.
Northwestern Gartersnakes hibernate throughout the winter in deep rock caverns or crevices, old mammal burrows, or other underground hollows that dip below the frost line. They emerge from the dens around March or April and are active until conditions are too cold, usually late October or November. Northwestern Gartersnakes, unlike the other Gartersnakes in British Columbia, are not very aquatic and seldom enter the water. Despite their terrestrial lifestyle, they are often found near aquatic habitats in areas that are densely vegetated like meadows, forest edges, estuaries, and beaches. Cover objects are important microhabitat features, affording shelter from predators and thermoregulatory opportunities.
Northwestern Gartersnakes typically mate in the spring, very shortly after they emerge from . Northwestern Gartersnakes are . The Northwestern Gartersnake has not been studied as heavily as the other Gartersnake species; thus, their mating habits are still largely a mystery. Females will give birth to anywhere from 3-20 young, depending on their size, in summer or early autumn. snakes are very small, ranging from 11-15 cm. Females may breed every year if healthy and well-fed, or every other year or every third year if in poor condition. Northwestern Gartersnakes can live for more than 20 years.
Northwestern Gartersnakes are primarily foragers, though they are generally “lazier” than the other Gartersnake species. However, the Northwestern Gartersnake does not need to be a particularly speedy hunter, as their favourite prey items are notoriously slow! Their favourite foods are slugs, earthworms, snails, and small amphibians. Once adults are large enough, they are particularly fond of eggs and will eat any eggs they can find.
The Northwestern Gartersnake appears to be very common within its range, and tends to outnumber other snake species that occupy the same habitats. Road mortality may be a significant threat for populations that are near busy roads. Habitat loss is a threat to all snake species but the Northwestern Gartersnake is apparently tolerant of low to moderate human disturbance.
Description
The Northwestern Gartersnake is the smallest Gartersnake in British Columbia, ranging in size from 35 – 75 cm, although most individuals tend to be less than 60 cm. Males are typically smaller than females, as increases with body size for females. The colour of Northwestern Gartersnakes varies more than any other snake species in British Columbia and melanistic and albino populations are more common than in other species. Most individuals are a dull brown-grey to olive, often with faint checkering on the dorsal surface and dorsal stripe. The colour of the dorsal stripe is incredibly variable and may be bright yellow, red, tan, blue, white, or cream. The width of the stripe is also highly variable, and some individuals will not possess a stripe at all. The belly is typically pale, and some individuals will have bold red or black markings. The scales of the dorsal surface are highly keeled, like all Gartersnakes in British Columbia. There is one characteristic that can help reliably identify a Northwestern Gartersnake: a pale upper lip with 7 upper scales.
Listen to the Indigenous words for “gartersnake” here!
Similar Species
The Northwestern Gartersnake may be easily confused with the Common Gartersnake and the Western Terrestrial Gartersnake. The Common Gartersnake is generally much larger, more likely to be black in background colour, and will often have red barring on the sides between the and stripes. The Western Terrestrial Gartersnake typically has 8 scales on the upper lip, two of them enlarged, and black spots that overlap with the dorsal stripe.
Credit: Gavin Hanke
Northwestern Gartersnake
Credit: Marcus Atkins
Common Gartersnake
Credit: Joe Crowley
Western Terrestrial Gartersnake
Distribution
The Northwestern Gartersnake has the smallest distribution of the three Gartersnake species in British Columbia, occurring from southwestern British Columbia to western Washington, Oregon, and California. Within British Columbia, Northwestern Gartersnakes are found on Vancouver Island and most of the Gulf Islands, the Lower Mainland, and inland to Manning Park. The largest populations tend to occur in the immediate coastal areas.
Habitat
Northwestern Gartersnakes hibernate throughout the winter in deep rock caverns or crevices, old mammal burrows, or other underground hollows that dip below the frost line. They emerge from the dens around March or April and are active until conditions are too cold, usually late October or November. Northwestern Gartersnakes, unlike the other Gartersnakes in British Columbia, are not very aquatic and seldom enter the water. Despite their terrestrial lifestyle, they are often found near aquatic habitats in areas that are densely vegetated like meadows, forest edges, estuaries, and beaches. Cover objects are important microhabitat features, affording shelter from predators and thermoregulatory opportunities.
Reproduction
Northwestern Gartersnakes typically mate in the spring, very shortly after they emerge from . Northwestern Gartersnakes are . The Northwestern Gartersnake has not been studied as heavily as the other Gartersnake species; thus, their mating habits are still largely a mystery. Females will give birth to anywhere from 3-20 young, depending on their size, in summer or early autumn. snakes are very small, ranging from 11-15 cm. Females may breed every year if healthy and well-fed, or every other year or every third year if in poor condition. Northwestern Gartersnakes can live for more than 20 years.
Diet
Northwestern Gartersnakes are primarily foragers, though they are generally “lazier” than the other Gartersnake species. However, the Northwestern Gartersnake does not need to be a particularly speedy hunter, as their favourite prey items are notoriously slow! Their favourite foods are slugs, earthworms, snails, and small amphibians. Once adults are large enough, they are particularly fond of eggs and will eat any eggs they can find.
Threats
The Northwestern Gartersnake appears to be very common within its range, and tends to outnumber other snake species that occupy the same habitats. Road mortality may be a significant threat for populations that are near busy roads. Habitat loss is a threat to all snake species but the Northwestern Gartersnake is apparently tolerant of low to moderate human disturbance.
Did You Know?
Because of their small size and lack of fangs or venom for protection, Northwestern Gartersnakes are an easy snack for predators like raptors, weasels, skunks, and other small carnivores. This is where the overwhelming variability in colour may be beneficial to these snakes. Research has shown that brightly coloured and striped individuals usually flee when they encounter a predator. The fast-moving stripes make it difficult for the predator to follow the snakes’ movements, confusing the predator and increasing the chances of escape. On the other hand, spotted, checkered, and faintly striped individuals have far greater camouflage and are less likely to be detected by predators.