OK, not very many people like snakes. But as mid-level predators, snakes are an important part of the food web: they serve as population controls for smaller animals like rodents, and are themselves food sources for larger predators like mammals and birds of prey. Over the past few years, snakes in the eastern part of the US have been struck with a deadly new disease caused by a fungus, which may be tied to global climate change.
The Daily Bucket is a regular series from the Backyard Science group. Here we talk about Mother Nature in all her glory, especially the parts that live nearby. So let us know (as close as you are comfortable) where you are and what's going on around you. What's the weather like? Seen any interesting plants, bugs or critters? Are there birds at your feeders? Deer, foxes or peahens in your yard? Seen any cool rocks or geological features? Post your observations and notes here. And photos. We like lots of photos. :)
In 2006, wildlife biologists were puzzled when they began to find endangered Timber Rattlesnakes in New Hampshire that were suffering from a disease that none of them had seen before: the snakes had large blisters and swellings in their skin, which then spread to the muscles and internal organs. The state's Timber Rattler population had already declined noticeably, and some herpetologists began to suspect that this disease had something to do with it. Those suspicions were strengthened a few years later when the same disease was found among declining populations of Massasauga Rattlesnakes in Illinois and Pygmy Rattlesnakes in Florida.
Researchers soon isolated a new variety of fungus from the infected snakes, which was named Ophidiomyces ophiodiicola. Since the disease had been first found in rattlesnake species, it was initially believed that it might be a condition that was limited to the viper family. This idea fell by the wayside, however, when the fungal disease was then seen in other groups, including water snakes, rat snakes, and racer snakes. By 2016, the disease had been confirmed in 14 different species of snake in 16 states--all of them in the eastern US. Most herpetologists believe that the actual extent is much wider, but because there are not very many people who are studying snakes in the wild, the disease may not be noticed in many areas.
In all of these cases, the Ophidiomyces fungus was found in the snake's skin, but it wasn't certain whether the fungus was actually causing the disease, or whether it was just opportunistically invading snakes that were already weak or sick from other causes. A 2015 study funded by the US Geological Survey solved the mystery: researchers inoculated a number of snakes with the fungus, and demonstrated that it was indeed the cause of the disease. Experiments showed that the fungus feeds by secreting chemicals that break down the protein keratin, which is the primary component of mammal hair and bird feathers. It is also what snake scales are made from. Apparently the fungus was moving onto the snake's skin and breaking down the keratin, producing the characteristic blisters and lesions.
In advanced stages, the fungus would move to attack the snake's bones and internal organs, but it may also kill the snakes earlier. Affected snakes often stopped eating, and shed their skins repeatedly to try to rid themselves of the infection. They also spent a lot of time basking in open sunlight in an apparent attempt to kill the fungus, but this left the snakes more exposed and vulnerable to predators. Because of all these factors, the death rate among infected snakes was over 90%.
Although ecologists now recognize that Snake Fungal Disease (SFD) may represent a serious threat to wild snake populations, much remains unknown. So far, the disease has only been found in the eastern half of the US and has not been seen in the West, and nobody knows why that is so. It is not clear why the fungus apparently favors snake scales, and does not seem to attack lizard scales or even mammalian fur or bird feathers, nor is there any good indication whether some snake species may be more or less vulnerable than others. It is also not known why the disease appeared suddenly in 2006 and had not been seen before then. Because there are so few researchers studying North American fungus species, very little is known about the Ophidiomyces. It's not even known if the fungus has recently been introduced to the US from somewhere else, bringing its snake disease with it, or if it is native to North America and has been here all along, but only became more virulent recently because of some environmental factor. Many biologists have pointed to other recent fungal outbreaks, such as Pseudogymnoascus destructans which causes lethal "white-nose disease" in bats and the chytrid fungus which has been attacking frog species, as indications that global climate change is altering the ecological map and enabling disease organisms to spread into areas that were previously unsuitable for them, where they can now infect populations that have no natural immunity.
We may not know for some time. Snakes are solitary animals which usually stay well-hidden, making it difficult to study them in the field. In the meantime, Snake Fungal Disease joins habitat loss as another factor that threatens their wild populations.
And now it is your turn: what are you seeing in your neck of the woods today?