An invasive species originating from East Asia, the Asian longhorned tick (Haemaphysalis longicornis) is now an established presence in the United States. Its discovery in New Jersey in 2017 marked its first detection outside of a port of entry. The primary concern surrounding this tick is its potential to form large infestations, which can pose a serious threat to the health of livestock. Its presence across numerous Eastern states has prompted ongoing surveillance and collaboration between state and federal agencies to monitor its movement and impact.
Identification and Geographic Distribution
Identifying the Asian longhorned tick can be challenging due to its small size and lack of distinctive markings. In its unfed state, the tick is a plain reddish-brown color and roughly the size of a sesame seed. After feeding, an adult female can swell to the size of a pea and take on a grayish-green color. Its name is derived from its prominent mouthparts, called palps, which give its head a “longhorned” appearance. This plain appearance can cause it to be confused with native U.S. tick species, particularly the rabbit tick and bird tick.
The Asian longhorned tick has spread significantly throughout the United States. As of 2024, its presence has been confirmed in a growing number of states, primarily concentrated in the mid-Atlantic, Northeast, and Southern regions. The tick thrives in a variety of environments, showing a preference for pastures, meadows, and the transitional zone between wooded areas and open fields. This habitat preference makes it a particular concern for grazing livestock. The tick’s expansion is actively monitored, with its known range now including states as far west as Missouri and Tennessee.
Asexual Reproduction and Rapid Spread
The ticks in North America are parthenogenetic, which means a female can produce offspring without mating with a male. This ability for a single female to essentially clone herself allows for rapid population growth from a very small introduction. A lone female can lay up to 2,000 eggs at a time, creating the potential for a new, dense population to emerge quickly.
This ability enables one tick, potentially transported on an animal, to establish a foothold in a new geographic area. Consequently, infestations can become extremely dense, with reports of thousands of ticks being found on a single host animal. This capacity for explosive population growth amplifies the tick’s impact on livestock and wildlife, making its spread a significant management challenge.
Risks to Humans and Animals
The primary threat from the Asian longhorned tick in the United States is to livestock and wildlife. Severe infestations on animals like cattle, sheep, goats, and deer can lead to substantial blood loss. This condition, known as anemia or exsanguination in extreme cases, causes stress, reduced growth, and can be fatal. Heavy infestations on cattle and white-tailed deer have been frequently reported.
The risks to humans and pets are centered on its potential to transmit diseases. In its native East Asia, the tick is a known vector for serious human illnesses, including Severe Fever with Thrombocytopenia Syndrome (SFTS) and Japanese spotted fever. While laboratory studies have shown the tick can carry the pathogen that causes Rocky Mountain spotted fever, it has not yet been found to be transmitting it to humans in the wild in the U.S. Its role as a disease vector in North America is still under intense investigation by scientists.
Prevention and Control Measures
Wearing clothing treated with permethrin or applying EPA-registered insect repellents containing substances like DEET or picaridin can reduce the risk of bites. After spending time in grassy or wooded areas, it is important to conduct thorough tick checks on your body and clothing. Promptly removing any attached tick by grasping it close to the skin with tweezers and pulling upward can help prevent potential pathogen transmission.
Pet owners should consult a veterinarian to select an appropriate and effective tick preventative product. For livestock producers, managing the landscape can decrease tick populations. Keeping pastures mowed and removing brush and leaf litter helps. Maintaining a buffer zone of at least nine feet between pastures and wooded areas also decreases tick populations. Regularly checking animals for ticks and consulting with a veterinarian or agricultural extension agent about approved treatments (acaricides) are also important.