Wisconsin DNR
Researchers examine a “tubed” timber rattlesnake for signs of snake fungal disease.
Ophidiomyces ophiodiicola, the scientific moniker for a pathogenic fungus that afflicts snakes, has been in Wisconsin for decades, at least, scientists think. The pathogen, whose name translates roughly to “snake-dwelling snake fungus,” has been surging in Wisconsin snake populations in recent years, causing more death and disease in Wisconsin snakes than anyone can remember.
The million-dollar question, researchers ask, is ‘why?’
“We don’t know exactly why it’s potentially emerging” as a more serious threat, explains Jeffrey Lorch, a microbiologist at the U.S. Geological Survey’s National Wildlife Health Center in Madison. “It’s probably widespread. It can affect a lot of different species.”
To be sure, the rising incidence of infection and mortality caused by the pathogen, known colloquially as snake fungal disease or SFD, is far from catastrophic in the Badger State. But in other states such as Illinois, where some snake species such as the massasauga rattlesnake are more confined in their range, there is a risk of losing species altogether.
“In other parts of the country, we’ve seen some significant impacts on snakes,” says Rich Staffen, a conservation biologist with the Wisconsin Department of Natural Resources, who notes that SFD has been a more dire problem in places like the northeastern United States where timber rattlesnake populations have been significantly affected. “We haven’t seen it at those levels in Wisconsin.”
To date, SFD has been documented in 12 of Wisconsin’s 21 species of snakes, according to Staffen, who, along with DNR herpetologist Rori Paloski, is leading the agency’s accelerated efforts to track the spread of the disease in Wisconsin. SFD has been confirmed in eight Wisconsin counties, including Dane, and clinical signs of the disease — open sores, especially near the eyes and mouth, and subcutaneous lumps — have been documented in snakes in eight other counties, mostly in southern and western Wisconsin, the parts of the state with the best habitats and climate for snakes, and which have the greatest diversity and abundance of snakes.
Although some people might cheer this development, it could have implications for the environment and human diseases.
Wisconsin DNR
A timber rattlesnake showing signs of the disease in and around the mouth.
The SFD fungus itself, says Lorch, is rarely the cause of snake mortality. Instead, its effects may make it harder for snakes to eat and drink and some die of starvation or dehydration. The disease may also inspire behaviors such as basking that make snakes more vulnerable to predators. And snakes, he adds, are more prone to fungal infections in general as fungi tend to prefer colder temperatures: “Snakes, being cold-blooded, do get fungal infections relatively commonly. Being the same temperature as the environment, they are more susceptible.”
The snakes themselves may change their behaviors in an effort to clear a fungal infection. Raising their body temperature by basking and shedding their skins or molting are two strategies snakes can employ. However, shedding is a big expenditure of energy for the snake and if the fungus has penetrated deeper into the flesh, molting may not be a successful strategy.
“A lot of these [afflicted] snakes are found out in the open,” Lorch says. “They are exhibiting some behaviors that may be an effort to fend off the fungus.”
Some snake species may be more at risk, and snakes that live at the fringes of their preferred habitats may also be vulnerable. Of special concern is the massasauga rattlesnake, one of only two species of venomous snakes (along with the timber rattlesnake) that live in Wisconsin.
“It is one of our key conservation concerns,” says the DNR’s Paloski of the massasauga, a species found mostly in wetlands in southwestern Wisconsin and one that the federal government lists as threatened.
The fungus is in the environment and snakes can become infected through exposure to spores in the soil, or they can pick it up from other snakes. Ingrained behaviors may be helping the fungus get a toehold as snakes tend to be communal as they bed down for the winter, gathering in rock crevices and dens to ride out the cold weather.
“We don’t know much about the fungus’ lifestyle,” says Lorch. “It does seem to be specific to snakes. It’s not a threat to humans. It proliferates in the outer layer of the [snake’s] skin initially, and then it penetrates deeper. It seems to infect more easily if there is a scrape or a scratch on the skin.”
The potential causes of the uptick in SFD in Wisconsin and other parts of the country remain speculative, but a changing climate is near the top of the list of suspects. Fungi thrive when it’s wet, and more frequent and heavier rainfalls, as Wisconsin has experienced in recent years, may be providing the SFD pathogen with the conditions it needs to thrive and successfully infect the snake hosts it depends on.
“It is completely sporadic, but something in the environment is making it go out of control,” Staffen notes.
There are probably a variety of factors at play, says the Wildlife Health Center’s Lorch. “There is not one magical thing that is making snakes more susceptible,” he says, noting that habitat loss is a bigger threat but could also be a contributing factor as snakes get crowded into smaller and smaller spaces.
Losing snakes from the landscape may not seem like a bad thing for some people as the animals generally don’t get great PR. But they are an essential part of the fabric of Wisconsin ecosystems, scientists say, and they play a big role controlling pests, especially rodents that may spread other diseases such as Lyme disease, and that pose a bigger risk to people. They are also a food source for lots of other animals. “It’s a very important prey species, especially for birds and some snakes eat other snakes,” explains Lorch.
“We don’t know what the impact of losing snakes would be on the environment or the food web,” Staffen says.
The small team of federal and state researchers agree that no one wants to find out.
See A Sick Snake? Do This
The DNR is seeking help tracking the spread of snake fungal disease in Wisconsin. Information and photographs of potentially infected snakes can help the effort. Pictures, along with the date of observation, an exact location, snake species and observed symptoms — lesions, scabs and lumps along the face and body — can be sent to DNRherptiles@wi.gov.
