Asian longhorned tick (Haemaphysalis longicornis)
The Asian longhorned tick (Haemaphysalis longicornis) is an invasive tick from East Asia. It was first confirmed in the United States in 2017. It is small and plain reddish-brown, with no special markings. In the US it reproduces without males. A single female can clone herself, laying hundreds to a few thousand eggs. So one host animal may carry a huge infestation. It is mainly a concern for livestock and animal health. It can spread Theileria orientalis (Ikeda) to cattle, causing bovine theileriosis. As of current CDC guidance, no human illness has been confirmed from its bite in the United States. Public health agencies are actively studying whether it could cause illness. It does not spread Lyme disease.
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How to identify it
- Small, plain reddish-brown to brown body with no white dot, stripe, or patterned shield. It is a plain (inornate) tick with nothing special to see with the naked eye.
- Short, stout mouthparts with tiny side spurs on the mouthpart base and palps. These spurs are the 'longhorns' it is named for. You can see them only with a magnifier.
- Rectangular festoons: small, block-like sections along the rear edge of the body. These are typical of Haemaphysalis ticks.
- In the US, nearly all ticks found are female. Only the all-female (parthenogenetic) form is established here, and males are almost absent. A single US male was confirmed only in 2025.
- A practical clue: many small ticks of several life stages swarming one animal strongly suggests this species. Native US ticks rarely infest a host in such numbers.
Size by life stage
All stages are small and easy to miss. Larvae are pinhead-sized (under ~1 mm) with six legs. Nymphs are about a poppy seed (~1.5 mm). An unfed adult female is about the size of a sesame seed (~2–2.6 mm long, ~1.5–1.8 mm wide). A fully fed female swells to the size of a pea, up to about 9–10 mm long.
Where it lives and when
Invasive and still spreading. It is not native to North America. It was first confirmed in the US in New Jersey in 2017. As of CDC's April 12, 2024 update, it had been found in 20 states, mostly in the eastern and mid-Atlantic US. These run from Massachusetts, Rhode Island, Connecticut, New York, and New Jersey south through Delaware, Maryland, Pennsylvania, Virginia, West Virginia, North Carolina, South Carolina, and Georgia. They reach west into Ohio, Indiana, Illinois, Kentucky, Tennessee, Missouri, and Arkansas. New finds are still being reported, for example in Iowa's Van Buren County in June 2025. Newer trackers cite 280+ counties across roughly 26 states. This range is its own, and it is still growing. Do not confuse it with any native tick's range. Check current CDC and USDA maps before relying on any exact count.
Season
Active through the warm months, with life stages overlapping in summer. A US study on Staten Island found that nymphs peak from mid-June to mid-July. Adults are most active in late July. Larvae peak in late summer (late August into September). At the peak of the season, all three stages can be found on one host at once.
Where it waits
- Livestock pastures and grazed grasslands, where the highest numbers are usually found
- Tall grass, brushy field edges, and overgrown fence lines
- Woodland edges and areas visited by white-tailed deer and other wildlife
- Overgrown yards and paddocks next to fields
Diseases it can carry
No major human disease is firmly established for this species in the U.S. Prevent bites regardless.
Look-alikes
Because it is plain reddish-brown with no markings, it is easy to confuse by eye with other small, plain ticks. These include rabbit and bird ticks (other Haemaphysalis species). They also include the nymphs or unfed adults of the blacklegged (deer) tick, brown dog tick, and Rocky Mountain wood tick. It lacks the Lone Star female's single white dot. It also lacks the mottled, patterned shield of the American dog tick and Gulf Coast tick. A reliable ID usually needs a magnifier (to see the mouthpart spurs) or lab testing. So send suspected ticks, especially many small ticks on one animal, to a state animal health lab, extension office, or health department.
Compare all tick speciesCommon questions
Is the Asian longhorned tick dangerous to people?
No human illness from its bite has been confirmed in the US. That is according to current CDC guidance. It also seems less attracted to people than native ticks. But it is a serious threat to livestock. Agencies are actively studying whether it could spread disease to people here. Prevent bites, and check pets and livestock for heavy tick infestations.
Does the Asian longhorned tick spread Lyme disease?
No. Lab studies show it cannot effectively spread the Lyme disease bacteria (it is not a competent vector). The same is true of human granulocytic anaplasmosis. In the US, Lyme disease is spread by blacklegged (deer) ticks, not this species.
Why can a single animal carry so many of these ticks?
Because females do not need males. In the US, only the all-female (parthenogenetic) form is established. A female can lay roughly 900–3,300 eggs without ever mating. Hundreds to thousands of ticks can then infest one host. This is a hallmark of the species and a warning sign for livestock owners.
Where in the US is the Asian longhorned tick found?
Mostly in the eastern, mid-Atlantic, and Midwestern US. It was first confirmed in New Jersey in 2017. As of CDC's April 12, 2024 update, it had been reported in 20 states. Its range is still growing (Iowa was added in 2025). Check current CDC and USDA maps for the latest counties.
Sources
- 1.Where Ticks Live (opens in a new tab) · CDC
The Lone Star tick is widely distributed in the Northeast, South, and Midwest U.S.
- 2.
- 3.TickEncounter Resource Center (opens in a new tab) · University of Rhode Island
Tick identification, prevention, and reporting resources.
- 4.
Educational information only, not medical advice. If you were bitten, use the tick bite tool and contact a licensed clinician if symptoms develop. Read our sources and disclaimer.