Are You My Mother?

Are You My Mother? Photograph by John Cancalosi

Beneath the sandstone slabs of Pennsylvania’s woodlands, female timber rattlesnakes (Crotalus horridus) gather to birth their young. In a single rookery, as many as 20 pregnant females might produce dozens of offspring. For a time following the big event, these communal maternity sites provide safe haven for the vulnerable new mothers as they recover from losing nearly half their body weight during birth. The sites also provide a safe space for the young snakes to begin to grow and develop—and to familiarize themselves with their species’ scent, information that will one day be critical to their survival.

Approximately one to two weeks after giving birth, the adult females leave the maternity chamber and their offspring to resume their lives as solitary predators. Eventually, though, they will make their way to another communal gathering, a wintering den in a crevasse deep underground, where, with dozens of other members of their species, they will wait out the freezing temperatures above. Yet, while adult rattlesnakes might have the luxury of retracing their own paths to these dens, first-year snakes must follow a route they’ve never traveled before, and that’s where their highly attuned sense of smell—and the memory of their mother’s scent—come into play.

Rattlesnakes pick up cues about their environment with both their nostrils and their tongues. After catching a whiff of something of interest, they will flick their tongues to capture molecules circulating in the air before delivering them to a highly specialized scent organ in the roof of their mouth. This organ enables snakes to identify the source of a number of scents in their environment, and, depending on which prong of the forked tongue captured the scent, the direction of that source. In this way rattlesnakes are able to follow a trail, whether they’re pursuing prey or seeking out long-lost kin.

While it’s hard for most of us to imagine a scent trail lasting for more than an hour or two, much less days or weeks, that is exactly what young timber rattlesnakes rely on to find their way to a safe and warm-ish place to spend the winter. And more often than not, they find their mothers (and brothers and sisters) there as well. A study published in 2018 found that not only are young timber rattlesnakes able to follow a week-old scent trail, but they appear to preferentially sniff out the trail and whereabouts of their mother and other kin over the trails of more distantly related individuals. There, deep underground with many of their closest family members alongside, these important predators cozy up for months on end before reemerging once again each spring.