Blacklegged Ticks in New Hampshire
This map is the result of 26 years of my active and passive surveillance on blacklegged tick (BLT) in New Hampshire. When I began, there were just three published records of this species in New Hampshire. This map compiles over 900 of my records, through December 1, 2015.
I conduct passive surveillance by keeping a log of tick samples submitted to UNH for identification. For many years this was the main way I followed blacklegged tick abundance and geographic spread. I decided to add active surveillance efforts in several years: 1989, 1990, 1991, 2013, 2014, 2015. I examined deer and moose at hunter check stations, flagged vegetation (dragged a sample cloth over it) in 90 towns (including all ten counties). In 2014 & 15 I focused on filling in minimally samples regions, including sections of Grafton and Coos counties. The map is incomplete, but is the best information on blacklegged tick abundance in our state that is currently available. I will continue to improve and update it.
The highest BLT populations seem to be in Rockingham, Strafford and Hillsborough counties, plus part of Merrimack county. In the 1990's, BLT's were most abundant within 15-20 miles of the coast, and within a mile or two of the major rivers and their tributaries. You can still see the "close to rivers" pattern by looking at the records that cluster along the towns bordering the Connecticut River. If I had shown the individual sample spots and their results, that pattern would be even more pronounced. Often in Grafton, Sullivan and Cheshire counties, I would find relatively high BLT numbers within a half mile of the Connecticut river, but much lower numbers only a mile or so to the east. Today's map clearly shows expansion beyond the 1990's pattern. It also suggests that the higher elevation areas seem to have lower BLT numbers.
Coos County has the lowest blacklegged tick populations in our state. I intensively sampled there in 2014 and 2015, yet came up with very few ticks. The very high numbers around Durham are partly an artifact of passive surveillance. You are more likely to submit a tick to us for identification, if you live close to UNH.
The NH Division of Health and Human Services plots reports cases of Lyme disease by town, and those maps are visible at their website at http://www.dhhs.nh.gov/dphs/cdcs/lyme/publications.htm%20They also show maps depicting the percent of BLT's that have the Lyme Disease organism, and other information.
Dr. Alan Eaton, Extension Specialist, Entomology
Click here for a printable map. The page size is 8 1/2 x 14".