Joining the “Dark Side”
Have you ever seen a black squirrel around Chicago? This squirrel, photographed by one our motion-triggered cameras, is not a rare species but rather an eastern gray squirrel with melanism.
Melanism is a genetic mutation in animals that creates an overabundance of the dark-pigments in their hair or skin, thereby making the individual black, or partly black if they are not fully melanistic. In some environments a mutation like this could be beneficial, making it harder for predators or prey to see the animal. For example, a melanistic squirrel may be less likely to be seen at night by a coyote or owl.
Mammals aren’t the only type of animals that can be melanistic. Fish, birds, arthropods and even reptiles can have this mutation.
In the past few months zoo staff have noticed a few melanistic garter snakes on or around zoo grounds. Garter snakes are quite common in Illinois, even in urban areas. While you might think these urban reptiles are visiting their relatives at the zoo, the more likely reason they’re here is due to the Lincoln Park Zoo’s proximity to open water.
These adaptable reptiles generally prefer to live near water and often eat smaller invertebrates by ambushing their prey and swallowing it whole. One way these garter snakes could potentially benefit from melanism while at Nature Boardwalk at Lincoln Park Zoo is by ambushing prey closer to the pond’s edge where the water-saturated soil is darker.
The way snakes are portrayed in movies—as insatiable predators—may make you feel a little uneasy about them. While some snake species can be threatening to humans if startled or injured, most want to avoid you as much as you want to avoid them. Furthermore, snakes and other reptiles play an important part in many ecosystems and contribute to a large part of biodiversity worldwide.
Like any type of wildlife you encounter throughout Chicago, it’s always best to observe at a distance. After all, most types of wildlife are more at risk from our presence than we are from theirs.
Mason Fidino is coordinator of wildlife management for Lincoln Park Zoo's Urban Wildlife Institute.