29th
2011
Tick Activity in Wintertime: My fascination with deer ticks, Ixodes scapularis, continues as we try to figure out how to hike in the woods without coming in contact with ticks during this warmer-than-usual-winter. I have come across two reliable studies on ticks.
My first source is from the Journal of Medical Entomology, July, 1995: Lower temperature limits for activity of several Ixodid ticks (Acari:Ixodidae): effects of body size and rate of temperature change. This article had a good table that gave me information about the Uncoordinated Activity Threshold of the blacklegged tick AKA deer tick AKA Ixodes scapularis (the temperature below which a tick can no longer seek a host in a coordinated manner; and ticks are active if temps. are above this temp. range) - The Uncoordinated Activity Threshold for ticks is as follows: Nymphs = 34.5F, Females = 41.1F, Males = 46F. I took the lower numbers in the mean. The Activity Threshold for Ixodes scapularis (The temperature at which all activity ceases and contacting a tick is not possible is as follows: Nymphs = 33.6F, Females = 33.9F, Males = 35.9F. I must note that I am not sure about the nymph numbers as the chart was difficult to read, but nymph numbers do not have much variability.
My second source is from the Hindawi Publishing Corporation - Interdisciplinary Perspectives on Infectious Diseases, 2009 - Effects of Climate Change on Ticks and Tick-Borne Diseases in Europe. This article gave me information about a related species of tick, Ixodes ricinus, in Sweden. These ticks can survive a 24 hour exposure to temperature ranges between -2F to 6F. Thirty-day exposure to outdoor high temperatures below 14F can be lethal to a high proportion of unfed nymphs.
Unfortunately, the way our climate is warming, it doesn’t look like the tick population will be decreasing any time soon. But, at least you know that you can traverse the woods safely when temps. are below 32F.
