Weird warm winter may or may not make ticks/Lyme worse
Seems like a no-brainer, doesn't it? The threat presented by the legions of ticks that were so active last fall — eager to latch onto hunters in the field — can only be worse after they survived the winter that wasn't.
I have been hearing unsubstantiated warnings that Lyme disease, a malady carried by deer ticks that has become a serious threat to Pennsylvanians, will be even more prevalent after the warm winter.
But it turns out it's not true – not necessarily, anyway. Ticks have become much more active in recent weeks, thanks to the 70-degrees-plus days much of the state experienced, but it is not true that there are more ticks because of the weirdly warm winter.
Still the ticks/Lyme disease threat may get more serious anyway.
Two ticks experts explain:
Dr Richard Ostfeld, a disease ecologist with the Cary Institute of Milbrook, N.Y., pointed out that the mild winter weather does not cause a rise in tick populations, although it can change tick behavior. Adult ticks are normally dormant in winter but can seek a host whenever temperatures rise several degrees above freezing.
The warm winter of 2011-2012 induced earlier than normal activity. While adult ticks can transmit Lyme, they are responsible for a small fraction of tick-borne disease, with spring-summer nymphs posing more of a human health threat.
"Warm weather means more-active, not more, deer ticks," Ostfeld said. "Spring humidity is what increases tick numbers, but the results of just-completed scientific studies reveal that when it comes to tick numbers, it's the weather of the next few months that will matter, not the weather of the last few."
According to Dr. Thomas Mather, Director of the Center for Vector-Borne Disease at the University of Rhode Island, while the warm weather increases tick activity in winter, it does not create or result in more of them.
It is another weather condition, the relative humidity, that affects their numbers.
"Spring ticks are just leftovers from the summer," Mather said "When the winter is warm, ticks are more active, so this past winter, the ticks were active almost every day."
The nymphs hatch in late May through mid June. They might hatch a week or so earlier during a warm spring like this one is starting out to be, Mather said, but the number of hatchings won't increase based on recent warm weather.
What matters for ongoing tick population numbers is the number of nymphs that survive, and that depends on the relative humidity when the nymphs hatch. Mather and a graduate student recently completed a 14-year research study using humidity monitors on Rhode Island.
They found that an 82 percent humidity rating is optimal for nymphs to hatch and survive. So if this turns out to be a humid spring — look out!
Humidity is also why piles of leaves and brush are good habitats for the ticks. Dense vegetation lets in less sunlight and is cooler than sunny areas. The dew point changes and water from the air condenses there.
The warmer winter could have some effect two years down the road, but only indirectly, Mather said. If it resulted in more deer, that could boost tick populations.
But no way I am going to talk about Pennsylvania deer numbers in this particular blog post — let's just stick to ticks.