Asian longhorned tick (Haemaphysalis longicornis)

How to identify it

• Small, plain reddish-brown to brown body with no white dot, stripe, or ornate shield pattern — an 'inornate' tick with nothing distinctive to the naked eye.
• Short, stout mouthparts bearing tiny lateral spurs on the basis capituli and palps (the 'longhorns' it is named for), visible only under magnification.
• Rectangular festoons — small block-like divisions along the rear body margin — typical of Haemaphysalis ticks.
• In the US, virtually all specimens are female: only the parthenogenetic (all-female) form is established here, and males are essentially absent (a single US male was confirmed only in 2025).
• Practical field clue: finding many small ticks of several life stages swarming a single animal strongly suggests this species — native US ticks rarely infest a host in such numbers.

Size: All stages are small and easily overlooked. Larvae are pinhead-sized (under ~1 mm) with six legs; nymphs are about a poppy seed (~1.5 mm); an unfed adult female is roughly a sesame seed (~2–2.6 mm long, ~1.5–1.8 mm wide). A fully engorged, blood-fed female swells to pea-sized — up to about 9–10 mm long.

Where it lives & when

Invasive and still expanding — not native to North America. First confirmed in the US in New Jersey in 2017. As of CDC's April 12, 2024 update it had been documented in 20 states, concentrated in the eastern and mid-Atlantic US: from Massachusetts, Rhode Island, Connecticut, New York, and New Jersey south through Delaware, Maryland, Pennsylvania, Virginia, West Virginia, North Carolina, South Carolina, and Georgia, and reaching west into Ohio, Indiana, Illinois, Kentucky, Tennessee, Missouri, and Arkansas — with new detections still being reported (for example, Iowa's Van Buren County in June 2025). Newer trackers cite 280+ counties across roughly 26 states. This is a distinct, actively growing distribution and should not be confused with any native tick's range; check current CDC/USDA maps before relying on any specific count.

Season: Active across the warm months, with overlapping life stages in summer. In US surveillance (Staten Island study), nymphs peak from mid-June to mid-July, adults are most active in late July, and larvae peak in late summer (late August into September); all three stages can be found on a single host at once during peak season.

• 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 frequented by white-tailed deer and other wildlife
• Overgrown yards and paddocks bordering fields

Diseases the asian longhorned tick 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 and unmarked, the Asian longhorned tick is easily confused by the naked eye with other small, unornamented ticks — especially rabbit and bird ticks (other Haemaphysalis species) and 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 and the mottled, ornate shield of the American dog tick and Gulf Coast tick. Reliable identification generally requires magnification (to see the mouthpart spurs) or lab confirmation, so suspected specimens — particularly many small ticks on one animal — should be submitted to a state animal-health laboratory, cooperative extension office, or health department.