Red-sided Garter Snake
Thamnophis sirtalis parietalis
6.9 mm
Length of ONE manually everted hemipenis (the right one), from where it leaves the tail base to its free tip; measured by us against the millimetre ruler in the published photo (Friesen et al. 2014, Fig. 1). Only one hemipenis is used per mating; the plate shows the pair
Spiny
A male garter snake has two hemipenes, each with a large spine at the base that works like a grappling hook during mating. The right one is larger, and males tend to alternate between them from one mating to the next.
Margin note: Keeps a spare.
Sources
- Friesen C.R., Uhrig E.J., Squire M.K., Mason R.T., Brennan P.L.R. (2014) Sexual conflict over mating in red-sided garter snakes (Thamnophis sirtalis) as indicated by experimental manipulation of genitalia. Proceedings of the Royal Society B 281(1774):20132694 doi:10.1098/rspb.2013.2694
- Lutterschmidt D.I., Lucas A.R., Karam R.A., Nguyen V.T., Rasmussen M.R. (2018) Sexually dimorphic patterns of cell proliferation in the brain are linked to seasonal life-history transitions in red-sided garter snakes. Frontiers in Neuroscience 12:364 doi:10.3389/fnins.2018.00364
- Shine R., Olsson M.M., LeMaster M.P., Moore I.T., Mason R.T. (2000) Are snakes right-handed? Asymmetry in hemipenis size and usage in gartersnakes (Thamnophis sirtalis). Behavioral Ecology 11(4):411–415 doi:10.1093/beheco/11.4.411
- Keeffe R.M., Zhang B., Anderson P.S.L., Brennan P.L.R. (2025) Evolutionary morphology of genital spines informed by puncture mechanics. Proceedings of the Royal Society B 292(2053):20251698 doi:10.1098/rspb.2025.1698
- Dowling H.G., Savage J.M. (1960) A guide to the snake hemipenis: a survey of basic structure and systematic characteristics. Zoologica 45(2):17–28 doi:10.5962/p.203350
- King R.B., Jadin R.C., Grue M., Walley H.D. (2009) Behavioural correlates with hemipenis morphology in New World natricine snakes. Biological Journal of the Linnean Society 98(1):110–120 doi:10.1111/j.1095-8312.2009.01270.x
Drawn from
- Friesen et al. 2014, Fig. 1: Photo, lateral view, of both hemipenes everted side by side under the tail base with a cm ruler: short spiny cylinders, basal spine (arrow) on the right hemipenis. Used for length, width and shape
- Dowling & Savage 1960, Text-fig. 5D: Drawing of a spinose hemipenis with basal hooks in the congener Thamnophis radix (note: T. radix is bilobed, unlike T. sirtalis; use only for the look of the basal hooks)
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