All protocols and procedures were approved by the Institutional Review Board of Columbia University (protocol AAAR3750) and an Institutional Animal Care and Use Committee (protocols AC-AAAX4454 and AC-AAAS6470). Sampling efforts on public lands began in June 2017 when 13 forest sites were surveyed for questing ticks. During June 30–August 10, 2017, we removed avian-derived ticks from mist-netted birds at Freshkills Park on Staten Island. During June 3–August 24, 2018, we surveyed 24 forest and grassland sites for questing ticks and 8 forested grid sites for questing and mammal-derived ticks. Questing ticks were obtained by dragging a 1-m² corduroy cloth over the leaf litter, which was checked every 10 m or 20 m and all attached ticks were removed. White-footed mice (Peromyscus leucopus) were trapped biweekly for 2 consecutive nights in Sherman live traps (https://www.shermantraps.com) separated by 10 m in 10 × 5 trap grids.

During August 5– 21, 2018, we anesthetized 16 male white-tailed deer (Odocoileus virginianus) and groomed them for ticks from 4 locations: College of Staten Island, Clay Pit Ponds, Mount Loretto State Forest and Freshkills Park. Mount Loretto State Forest, and Freshkills Park are dominated by grassland and wetland ecosystems, and Clay Pit Ponds is characterized by dense forest. College of Staten Island has manicured landscaping with grass and forest (separated by fencing) along the perimeter. While deer were anesthetized, we checked antlers, ears/head, front legs, hind legs, and body for ticks. Each animal was screened for 15 min to minimize time spent under anesthesia. Ticks were removed with forceps and stored in 100% ethanol for later identification.

During June 6–July 13, 2018, tick sampling was conducted on residential properties, which were selected by using a random cluster sampling strategy within areas previously identified as high risk given their proximity to parks (within 100 m). Houses were visited once, and questing ticks were collected along property edges by using the same method as in public parks.

Figure 1

Figure 1. Seasonal activity of Haemaphysalis longicornis ticks (adults, nymphs, and larvae), Staten Island, New York, USA. Questing ticks were pooled by 2-week collection sessions during June 3–August 23, 2018.

We found questing H. longicornis ticks at 7 of 13 parks surveyed in 2017 and 16 of 32 parks surveyed in 2018 (Table 1). Adult ticks were most active in late July and nymphs were active from mid-June to mid-July, similar to findings in South Korea (11). Larvae showed highest proportional activity in late August (Figure 1). We identified ticks primarily by morphology; a representative sample of specimens from deer and drag collections (n = 63) were confirmed as H. longicornis ticks by DNA barcoding using the cytochrome c oxidase I locus (12).

In 2017, we processed 39 birds: 11 American robins (Turdus migratoriu), 1 common yellowthroat (Geothlypis trichas), 20 gray catbirds (Dumetella carolinensis), 2 house wrens (Troglodytes aedon), 1 indigo bunting (Passerina cyanea), 3 northern cardinals (Cardinalis cardinalis), and 1 American yellow warbler (Setophaga petechia). We found no H. longicornis ticks of any life stage. We found no H. longicornis ticks on 87 uniquely tagged P. leucopus mice (190 individual captures), 2 eastern chipmunks (Tamias striatus), 14 northern short-tailed shrews (Blarina brevicauda), and 1 brown rat (Rattus norvegicus). All life stages were recovered from deer at all 4 locations, and larvae were the most prevalent stage collected (Table 2). These findings indicate that immature stages of these ticks might feed exclusively on white-tailed deer or unsampled medium-sized animals. The high proportion of larvae on deer was probably caused by sampling during peak larval activity.

Figure 2

Figure 2. Sampling site locations and number of Haemaphysalis longicornis ticks collected on deer, in parks (grids and transects), and during household visits on Staten Island, New York, USA.

We surveyed 135 residential properties (average size 1,455 m²) (total visited = 505), of which 80% were located adjacent to parks in south and central Staten Island (Figure 2). Ticks were present at 34.1% of inspected properties. H. longicornis nymphs (n = 16) were found at 5 properties (in tall grass and shaded lawns), all located in the southern section of the island; no other life stages were found.

The ability of H. longicornis ticks to feed on a wide range of domestic and wildlife hosts, reproduce asexually, and survive various environmental conditions likely contributed to their establishment throughout the eastern United States. All 3 life stages were found feeding on white-tailed deer in August, together with 2 other established tick species (A. americanum and I. scapularis). Pathogen transmission by co-feeding has been documented in field and laboratory studies (13,14) and could be a potential mechanism for H. longicornis ticks acquiring pathogens when feeding alongside infected A. americanum or I. scapularis ticks.

We found no H. longicornis ticks on P. leucopus mice or avian hosts even in sites with high densities of questing ticks, limiting the potential for this tick to acquire human pathogens. In New Zealand, immature life stages were commonly found on hares and goats, and adults were frequently found on larger mammals; the brown hare (Lepus europaeus) was touted as a major disseminator (9,15). These findings indicate the need for extensive sampling of other mammalian hosts. Finding H. longicornis ticks on residential properties is a human health concern because its potential as a vector of human pathogens in the United States is unknown. The combination of suitable habitat types, a plethora of host species, and high humidity make most regions of the United States suitable for H. longicornis tick establishment and proliferation.