Initial detection of Haemaphysalis longicornis (Acari: Ixodidae) in Michigan.

The invasive tick Haemaphysalis longicornis Neumann (Asian longhorned tick) was first detected in the Mid-Atlantic region of the United States of America in 2017, prompting concerns about the introduction and establishment of this exotic pest. As of April 2025, H. longicornis expanded to 21 eastern and midwestern states. Haemaphysalis longicornis is a cattle pest that can cause anemia and exsanguination and is a vector of the parasite Theileria orientalis Ikeda. This report describes the first detection of H. longicornis in Michigan during surveillance for host-seeking ticks of public health concern. Ticks were collected via drag sampling from May to July 2025 at Grand Mere State Park (GMSP, Berrien County), located along Lake Michigan ∼30 km north of the Indiana border. Three H. longicornis nymphs were collected 30 May, 6 June, and 11 June. After detection of the first specimen, GMSP was revisited 6 times (total drag distance = 19,920 m2). Five other species were collected during surveillance for H. longicornis, including 302 specimens of the emerging Amblyomma americanum Linnaeus (lone star tick) and 1 A. maculatum Koch (Gulf Coast tick), the latter of which was not previously reported at this site or surrounding areas. One road-killed Odocoileus virginianus Zimmermann (white-tailed deer) was sampled for ticks ∼10 km south of GMSP. While no H. longicornis were detected, 13 A. americanum and 1 A. maculatum were found on this deer. Continued surveillance at GMSP and in the surrounding area is necessary to evaluate the potential distribution of H. longicornis in southwest Michigan.