Invisible Trail

Garter snake with its jaw openPhoto Courtesy of Paul Hancock A few weeks after the snakes emerge from the dens, the mating ritual appears to be over as quickly as it began. After a female snake has mated, she immediately leaves the area of the dens to find a comfortable spot to eat and to produce her young. Each of the males will stay around the dens until the last of the females has mated and left. These male snakes will remain at the dens for four to six weeks, hoping to mate before beginning their search for food. Their body weight drops a considerable amount during this time; however, because they are not incubating their young, the loss of nutrition is not as significant a factor as it would be to the females. Each of the snakes moves off in a different direction searching for the all-important area with an abundance of food.

By late summer or early fall, each of the females will have given birth to her babies and each of the adult male and female snakes will begin their trek back to the dens in anticipation of the coming cold weather. Researchers have always wondered how the snakes were able to almost instinctively know where to go each year. The discovery of the pheromone posed a possible answer for these researchers. They hypothesized that perhaps the same pheromones which assisted in the mating ritual were responsible for telling the snakes which way to go.

boardwalkGarter snakes can follow a pheromone trail left in the grass. Photo Courtesy of Paul Hancock To test this theory, a snake was placed on a wooden maze shaped like the letter “Y.” Drops of the snake pheromone were dabbed on only one “arm” of the maze. The male snake was started at the bottom of the “y” and when he reached the fork could choose to go either left or right. After stopping and flicking out his tongue a few times, the snake darted off in the direction of the dabbed pheromone. To ensure that this would happen on a consistent basis, many different snakes were tested, with the pheromone placed on a different section each time. Each time the snake would go in the direction of the pheromone. This seemed to prove that the snakes were indeed using pheromones to determine which way to go. This could help determine why the snakes knew how to get to the marshes. But this was a small test conducted on a surface that was not familiar to the snakes. What would happen if the snakes were to try to follow the pheromone path in the grass?

In this test, the snake was placed inside a container in the middle of a three-meter circle. A few drops of the pheromone were placed in a specific path in the circle. Once the snake was released from the container, it quickly began on a very specific course as if it were being directed by street signs. The course the snake had chosen was the one mapped out by the drops of the pheromone. It seemed as though the snakes were indeed choosing their course based on that which the other snakes had taken.