Blacklegged Ticks in New Hampshire

This map is the result of 25 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 700 of my records, through late November 2013.

I conduct passive surveillance by keeping a log of tick samples submitted to UNH for identification. Active surveillance includes 4 years (1989, 1990, 1991, 2013) of examining deer at hunter check stations, two years of searching moose at hunter check stations, and two years (2012 and 2013) of flagging vegetation (dragging a sample cloth over it) in 8 counties. In 2014 I am focusing on sampling in Grafton and Coos counties, which to this point have been minimally sampled. The map is incomplete, but is the best information on blacklegged tick abundance 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. 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 is largely blank because of a lack of sampling effort. With luck, I may have a more complete picture soon. 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  They 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.