Both colorless and odorless, pheromones are produced by animals to stimulate behavioral responses in other animals of the same species. They’re primarily used for communication and mating. The vast majority of the research on pheromones and snakes has been conducted on the red-sided garter snake because they're the most abundant snakes in North America. According to National Geographic, the site used by numerous research teams in Manitoba, Canada, is famous for the thousands of snakes that leave hibernation dens each spring.
How Snakes “Smell” Pheromones
While snakes do have nostrils to breathe with, they don’t use nostrils to smell. Snakes are able to detect pheromones and other scent particles by flicking their tongues. The sex pheromones of snakes are made up of larger molecules and don’t float through the air like they do in other species, so the snake’s tongue actually has to touch the skin of the other snake. A sensitive organ in the roof of a snake's mouth called Jacobson’s organ identifies which type of pheromone it is.
Even though estrogen is not a pheromone, it's an essential precursor to the production of pheromones in female snakes. A 2011 study of garter snakes in Manitoba shed light on the link between estrogen and pheromones. The research team led by Robert Mason, a zoology professor at Oregon State University, implanted male red-sided garter snakes with a capsule containing estrogen matching female garter snakes. After a year’s exposure to estrogen, the male garter snakes began producing female sex pheromones. The result was the non-implanted males clustered around the implanted males in attempts to mate as if they were females.
Mating & Pheromones
The sex pheromone female snakes emit tells the males which species of snake she is, her gender, size, age and reproductive condition. For red-sided garter snakes, the larger and longer female snakes produce more babies and offer an increased chance of successful reproduction, so males are more attracted to them. Competition is fierce for the longer females. Writhing clusters of red-sided garter snakes called mating balls composed of up to 100 male snakes vie for the attention of the sole female in the group. Once the female has successfully mated, she emits a different pheromone indicating she's no longer available.
The male red-sided garter snakes of Canada survive the harsh winters by hibernating underground in dens shared by thousands of other garter snakes. When spring comes and they emerge, they are cold and slow moving, making them easy prey for crows and other predators. Some of the male garters have a unique survival technique called female mimicry. They emit female pheromones that attract other males, fooled into thinking the he’s a she. The sham males end up on the bottom of the mating ball, benefiting from the warmth of the other males. The result is the sham males warm up faster. Mason’s research discovered the sham males were more frequently successful in mating with females, in comparison to the males who didn’t emit female pheromones.
- National Geographic: Some Snakes Find Safety in "Cross-Dressing"
- San Diego Zoo: Retiles: Snake
- Live Science: Estrogen Turns Male Snakes into Same-Sex Charmers
- The Journal of Experimental Biology: How to Make a Sexy Snake: Estrogen Activation of Female Sex Pheromone in Male Red-sided Garter Snakes
- BBC World: Male Snakes Con Females to Keep Warm
- National Center for Biotechnology Information: Female Mimicry in Garter Snakes.
- Division on Earth & Life Sciences of National Academy of Sciences: The Male Red-sided Garter Snake (Thamnophis sirtalis parietalis): Reproductive Pattern and Behavior
- Hemera Technologies/PhotoObjects.net/Getty Images