Ticks of Delaware revisited: an updated checklist of hard ticks (Ixodidae) and first records of soft ticks (Argasidae) in the First State

Abstract

It has been more than three-quarters of a century since the inaugural report of Delaware’s ticks was published. To provide an updated checklist of tick species currently known to occur in Delaware, we reviewed the scientific literature, examined tick collections, accessed archived tick specimen data, and analyzed findings from the state’s ongoing tick surveillance program, initiated in 2019. We report here a total of 15 established hard tick species (Ixodidae), as well as additional Ixodidae and 2 soft tick species (Argasidae) that are not yet confirmed as established. We summarize the phenology of each species and its known distribution in Delaware and public health importance. We also provide a table of known tick-host associations for Delaware.

Introduction

Since the original checklist of Delaware ticks was published (MacCreary 1945), new tick species have been detected, new tick-host associations have been documented, and new tick-borne viruses, bacteria, and parasites known to be pathogenic to humans, companion animals, or livestock have been described. In the first-published Delaware tick checklist, MacCreary (1945) considered the American dog tick (Dermacentor variabilis (Say)) the only significant tick threat to humans in Delaware. Today, that threat has been surpassed in medical importance by the blacklegged tick (Ixodes scapularis Say), a vector of the causative agents of Lyme disease, babesiosis, anaplasmosis, and other diseases, and the lone star tick (Amblyomma americanum (L.)), the vector of pathogens causing ehrlichiosis and tularemia and strongly associated with alpha-gal syndrome (Eisen 2022).

Delaware is located in the Mid-Atlantic region of the United States and comprises 3 counties (New Castle, Kent, and Sussex, from north to south). Most of the state is located in the Atlantic Coastal Plain; part of northern New Castle County is in the Appalachian Piedmont. While it is the second smallest state in the United States by area, and the sixth smallest by population, Delaware shoulders an outsize share of the national tick-associated disease burden: it is in the top 10 states for incidence rates of Lyme disease (Schwartz et al. 2017), ehrlichiosis (Heitman et al. 2016), and spotted fever rickettsioses (Drexler et al. 2016), and it is a high-incidence state for alpha-gal syndrome (Thompson 2023). Survey results indicate that tick literacy and public concern for tick-associated diseases remain low in Delaware (Gupta et al. 2018).

In recent years, researchers have filled important gaps in vector-borne pathogen research in Delaware. For example, Shifflett et al. (2023) evaluated the diversity of the outer surface protein C gene in Borrelia burgdorferi bacteria from blacklegged ticks across Delaware. Peterson et al. (2024) reported the first triatomine kissing bug infected with Triatoma cruzi in Delaware, and an updated checklist of Delaware fleas is now available (Kennedy et al. 2024). Our objective was to research available literature, specimens in local collections and in national museums, as well as recent field surveys of ticks in the environment and from hosts to create an updated list of the tick species in Delaware and assess their risk to public health.

Materials and Methods

We conducted a literature review using JSTOR and Google Scholar to identify publications mentioning ticks in Delaware. Search terms included “ticks, Delaware,” “Ixodes, Delaware,” “Amblyomma, Delaware,” and iterations thereof. Additionally, we checked websites that aggregate natural history observations from the public, specifically, BugGuide.net, iNaturalist.org, and reddit.com/r/whatsthisbug/ to find additional records, and when an apparently new species was documented in this way, we contacted the user(s) in an effort to acquire specimens for confirmation.

We collected ticks year-round during routine active and passive surveillance activities, including dragging vegetation on public lands and crowd-sourcing ticks from veterinary clinics, wildlife rehabilitators, and other facilities and professionals that work with animals. We collected ticks from roadkill and from birds that collided with buildings, and from hunter-harvested game, namely white-tailed deer (Odocoileus virginianus (Zimmermann)), sika deer (Cervus nippon Temminck), and wild turkeys (Meleagris gallopavo L.). We additionally collected ticks from small mammals trapped with Sherman live traps (H.B. Sherman Traps, Tallahassee, FL) or Victor Mouse and Museum Special snap traps (Woodstream Corporation Inc., Lancaster, PA), from mesopredators such as red foxes (Vulpes vulpes (L.)), gray foxes (Urocyon cinereoargenteus (Schreber)), and raccoons (Procyon lotor (L.)) that were trapped and removed from public lands to protect nesting threatened and endangered shorebirds, and from other mammals, such as beavers (Castor canadensis Kuhl) and groundhogs (Marmota monax (L.)) that were trapped to reduce human-wildlife conflict (Delaware Department of Natural Resources and Environmental Control Nuisance Wildlife Control Operator Permit #095).

We examined tick specimens collected in Delaware and housed in the University of Delaware collection (UDCC) and the Delaware Museum of Nature and Science (DMNH, formerly Delaware Museum of Natural History). We also accessed tick specimen data archived by the University of Georgia College of Veterinary Medicine’s Southeastern Cooperative Wildlife Disease Study (SCWDS), the Defense Centers for Public Health– Aberdeen Vector-Borne Disease Branch (DCPH-A), the United States Department of Agriculture Animal and Plant Health Inspection Service National Veterinary Services Laboratories (NVSL), and the Smithsonian Institution’s National Tick Collection (USNTC).

Ticks were identified to species, sex (adult specimens only), and life stage using published keys (Clifford et al. 1961, Keirans and Litwak 1989, Durden and Keirans 1996, Egizi et al. 2019). Tick species were deemed “established” if they met criteria outlined in Dennis et al. (1998), ie if at least 6 individual ticks, or individuals representing 2 of 3 motile life stages, were reported or collected within the span of 1 yr.

DNA Barcoding

To support morphological identification of new state records, DNA from a subset of ticks was extracted using a nondestructive procedure, and the barcoding locus cytochrome oxidase I (cox1) was amplified and sequenced as described in Egizi and Maestas (2022). Briefly, a sliver of the posterolateral idiosoma was removed with a sterile scalpel to allow lysis buffer (Qiagen Buffer ATL + Proteinase K) to penetrate the tissues and specimens were lysed overnight at 56 °C. After incubation ticks were returned to ethanol-filled vials for permanent storage while the lysis buffer was extracted with a Qiagen DNeasy Blood & Tissue kit (Qiagen Inc., Valencia, CA). A 656 bp fragment of the mitochondrial cytochrome oxidase I (cox1) locus was amplified with primers chelicerate Fw and chelicerate Rv (Barrett and Hebert 2005), visualized on a 2% agarose electrophoresis gel, purified with ExoSAP-IT (USB Corporation, Cleveland, OH) and sequenced in both directions (Azenta/Genewiz, South Plainfield, NJ). Sequences were trimmed and aligned in Geneious 11.1.5 (Kearse et al. 2012) and compared with known tick cox1 sequences in NCBI BLASTn (Altschul et al. 1990) searches.

Results

We provide here a summary of each species reported or collected in Delaware (Table 1), listed in alphabetical order by family, genus, and species. Known host associations for each tick species in Delaware are provided in Table 2.

Table 1.

Annotated list of the ticks (Ixodida: Argasidae, Ixodidae) of Delaware, with first known vouchered specimen (DMNH or USNTC) and accompanying data.

Species	Accession No.	Date collected	Location	Sex, stage	Source	Reference
Argasidae
Alectorobius kelleyi (Cooley and Kohls)	DMNH 2024.MOL.012-01	Mar 2023	Newark, New Castle Co.	1	Human residence	This study
Argas sp.	USNMENT1786507	June 2021	Milford, Kent Co.	1♂	Homo sapiens (unattached)	This study
Ixodidae
Amblyomma americanum (L.)	USNMENT1512897	15 Nov 2019	New Castle Co.	1N	Odocoileus virginianus	This study
Amblyomma maculatum Koch	USNMENT1512913	9 June 2020	New Castle Co.	3♂, 3♀	Homo sapiens	This study
Dermacentor albipictus (Packard)	USNMENT1512912	14 Nov 2021	New Castle Co.	1♀	Odocoileus virginianus	This study
Dermacentor variabilis (Say)	RML18478	10 May 1940	New Castle Co.	1♂	Canis lupus familiaris	MacCreary 1945
Haemaphysalis leporispalustris (Packard)	USNMENT1512902	18 June 2019	Kent Co.	1♀	Sylvilagus sp.	This study
Haemaphysalis longicornis Neumann	USNMENT1512903	4 July 2020	Newark, New Castle Co.	2♀	Canis lupus familiaris	This study
Ixodes banksi Bishopp	DMNH 2024.MOL.012-23	April 2023	Hartly, Kent Co.	1N	Castor canadensis	This study
Ixodes brunneus Koch	USNMENT1512908	Jan 2021	Viola, Kent Co.	1♀	Mimus polyglottos	Kennedy and Winter 2022
Ixodes cookei Packard	RML16050	30 June 1939	Kent Co.	2♂, 2♀	Vulpes vulpes (“Vulpes fulva”)	MacCreary 1945
Ixodes dentatus Marx	RML 121215	15 Aug 1939	New Castle Co.	1♂, 2♀	Sylvilagus floridanus	N/A
Ixodes keiransi Beati, Nava, Venzal, and Guglielmone	DMNH 2024.MOL.012-28	April 2023	Milford, Kent Co.	1♀	Environment	This study
Ixodes marxi Banks	RML57133	May 20 1941	New Castle Co.	1♀, 1N	Tamiasciurus hudsonicus (Erxleben)	MacCreary 1945
Ixodes scapularis Say	RML 116166	28 Nov 1982	Newark, New Castle Co.	1♂, 2♀	Canis lupus familiaris	N/A
Ixodes texanus Banks	RML33546	28 Nov 1953	Sussex	1♀, 1N	Procyon lotor	Darsie and Anastos 1957
Rhipicephalus sanguineus (Latreille)	USNMENT1786488	9 June 2021	New Castle Co.	1♀	Canis lupus familiaris	This study

Table 2.

Known tick-host associations in Delaware. Scientific and common host names are those currently recognized as valid by the Integrated Taxonomic Information System (https://www.itis.gov). Where applicable, accession numbers for voucher specimens at the USNTC and DMNH are provided.

Tick (scientific name)	Tick (common name)	Host (scientific name)	Host (common name)	Reference
Argas sp.	Soft tick	Homo sapiens	Human (not attached)	This study (USNMENT1786507)
Amblyomma americanum	Lone star tick	Canis lupus familiaris	Domestic dog	This study
		Vulpes vulpes	Red fox	This study (USNMENT1786508)
		Urocyon cinereoargenteus	Gray fox	This study (DMNH 2024.MOL.012-03)
		Ursus americanus Pallas	American black bear	This study (DMNH 2024.MOL.012-06)
		Procyon lotor	Raccoon	This study (USNMENT1786500)
		Felis catus L.	Domestic cat	This study (DMNH 2024.MOL.012-05)
		Homo sapiens	Human	MacCreary 1945, Mellott and Connell 1965; NVSL records (1973); DCPH-A records (1998-2019); this study (USNMENT1512913)
		Odocoileus virginianus	White-tailed deer	Wolfe 1994; this study (USNMENT1512897)
		Capra hircus L.	Domestic goat	This study (DMNH 2024.MOL.012-07)
		Sciurus carolinensis Gmelin	Eastern gray squirrel	This study (USNMENT1512896)
		Sciurus niger cinereus L.	Delmarva fox squirrel	This study (USNMENT1512898)
		Marmota monax	Groundhog	This study (DMNH 2024.MOL.012-04)
		Meleagris gallopavo	Wild Turkey	This study (USNMENT1786501)
		Bubo virginianus (Gmelin)	Great Horned Owl	SCWDS records (2018)
		Accipiter cooperii (Bonaparte)	Cooper’s Hawk	SCWDS records (2018)
		Buteo jamaicensis (Gmelin)	Red-tailed Hawk	UDCC records (DMNH 2024.MOL.012-02)
		Spizella pusilla (Wilson)	Field Sparrow	This study
Amblyomma maculatum	Gulf Coast tick	Canis lupus familiaris	Domestic dog	This study (USNMENT1786503)
		Vulpes vulpes	Red fox	This study (DMNH 2024.MOL.012-08)
		Homo sapiens	Human	This study (USNMENT1786502)
		Odocoileus virginianus	White-tailed deer	This study (USNMENT1786495)
		Peromyscus leucopus	White-footed mouse	This study
Dermacentor albipictus	Winter tick	Canis lupus familiaris	Domestic dog	This study (DMNH 2024.MOL.012-12)
		Felis catus	Domestic cat	This study
		Homo sapiens	Human	This study (DMNH 2024.MOL.012-09)
		Odocoileus virginianus	White-tailed deer	Wolfe et al. 1994; this study (USNMENT1512912);
Dermacentor variabilis	American dog tick	Didelphis virginiana Kerr	Virginia opossum	MacCreary 1945, Mellott and Connell 1965, NVSL records (1973); this study
		Canis lupus familiaris	Domestic dog	MacCreary 1945, Mellott and Connell 1965; NVSL records (1965); this study (DMNH 2024.MOL.012-16)
		Vulpes vulpes	Red fox	MacCreary 1945; this study (USNMENT1786496)
		Procyon lotor	Raccoon	NVSL records (1973); this study (USNMENT1786497)
		Ursus americanus	American black bear	This study (DMNH 2024.MOL.012-19)
		Mephitidae	Skunk	MacCreary 1945, Mellott and Connell 1965
		Felis catus	Domestic cat	This study; MacCreary 1945, Mellott and Connell 1965
		Homo sapiens	Human	This study; Mellott and Connell 1965; NVSL records (1966, 1973); DCPH-A records (1998-2008, 2010-2019)
		Equus caballus L.	Horse	MacCreary 1945, Mellott and Connell 1965
		Sus scrofa L.	Pig	MacCreary 1945, Mellott and Connell 1965
		Bos taurus	Domesticated cattle	MacCreary 1945, Mellott and Connell 1965, NVSL records (1965, 1966, 1970, 1972)
		Capra hircus	Domestic goat	This study (DMNH 2024.MOL.012-18)
		Blarina brevicauda (Say)	Northern short-tailed shrew	This study
		Sylvilagus floridanus	Eastern cottontail	MacCreary 1945, Mellott and Connell 1965, Doss et al. 1974
		Microtus pennsylvanicus	Meadow vole	This study; MacCreary 1945, Mellott and Connell 1965
		Microtus pinetorum (Le Conte)	Woodland vole	MacCreary 1945, Mellott and Connell 1965
		Peromyscus leucopus	White-footed mouse	This study (DMNH 2024.MOL.012-14); MacCreary 1945, Mellott and Connell 1965
		Oryzomys palustris	Marsh rice rat	This study (DMNH 2024.MOL.012-13)
		Mus musculus L.	House mouse	MacCreary 1945, Mellott and Connell 1965
		Rattus norvegicus (Berkenhout)	Brown rat	MacCreary 1945, Mellott and Connell 1965
		Zapus sp.	Jumping mouse	MacCreary 1945, Mellott and Connell 1965
		Sciurus carolinensis	Eastern gray squirrel	This study (USNMENT1512901); MacCreary 1945, Mellott and Connell 1965
		Marmota monax	Groundhog	This study (DMNH 2024.MOL.012-17); MacCreary 1945, Mellott and Connell 1965
Haemaphysalis leporispalustris	Rabbit tick	Sylvilagus sp.	Rabbit	This study (USNMENT1512902); MacCreary 1945, Mellott and Connell 1965
		Buteo jamaicensis	Red-tailed Hawk	UDCC records (DMNH 2024.MOL.012-20)
		Turdus migratorius L.	American Robin	Peters 1936; Doss et al. 1974
		Dumetella carolinensis (L.)	Gray Catbird	DMNH specimen (2022)
		Toxostoma rufum (L.)	Brown Thrasher	SCWDS records (2019)
		Sturnus vulgaris L.	European Starling	Peters 1936; Doss et al. 1974
		Cardinalis cardinalis	Northern Cardinal	DMNH specimen (2023)
		Melospiza melodia (Wilson)	Song Sparrow	Peters 1936
		Seiurus aurocapilla (L.)	Ovenbird	DMNH specimen (2006)
		Agelaius phoeniceus (L.)	Red-winged Blackbird	Peters 1936
		Quiscalus quiscula (L.)	Common Grackle	Peters 1936, Doss et al. 1974
Haemaphysalis longicornis	Asian longhorned tick	Canis lupus familiaris	Domestic dog	This study (USNMENT1512903)
		Vulpes vulpes	Red fox	This study (USNMENT1786491)
		Felis catus	Domestic cat	This study
		Homo sapiens	Human	This study (DMNH 2024.MOL.012-22)
		Odocoileus virginianus	White-tailed deer	This study (USNMENT1786490)
		Sylvilagus sp.	Domestic rabbit	This study
		Marmota monax	Groundhog	This study (DMNH 2024.MOL.012-21)
		Buteo jamaicensis	Red-tailed hawk	SCWDS records (2020)
Ixodes banksi	Beaver tick	Castor canadensis	American beaver	This study (DMNH 2024.MOL.012-23)
Ixodes brunneus		Mimus polyglottos	Northern Mockingbird	Kennedy and Winter 2022 (USNMENT1512908)
Ixodes cookei	Groundhog tick	Vulpes vulpes	Red fox	USNTC (RML 16050); this study (DMNH 2024.MOL.012-25)
		Procyon lotor	Raccoon	NVSL records (1973); this study (USNMENT1786492)
		Mustela putorius furo L.	Domestic ferret	This study (DMNH 2024.MOL.012-32)
		Marmota monax	Groundhog	This study
Ixodes dentatus		Sylvilagus sp.	Rabbit	MacCreary 1945, Mellott and Connell 1965; DMNH 2024.MOL.012-26
		Sylvilagus floridanus	Eastern cottontail	USNTC (RML121215)
		Microtus pennsylvanicus	Meadow vole	MacCreary 1945 (reported as “meadow mouse”)
Ixodes keiransi		Blarina brevicauda	Northern short-tailed shrew	This study (DMNH # 2024.MOL.012-27)
Ixodes marxi		Tamiasciurus hudsonicus	Red squirrel	MacCreary 1945, Mellott and Connell 1965; USNTC (RML 57133)
Ixodes minor		Cardinalis cardinalis	Northern Cardinal	Adalsteinsson 2016
		Pipilo erythrophthalmus	Eastern Towhee	Adalsteinsson 2016
Ixodes scapularis	Blacklegged tick	Canis latrans	Coyote	DMNH specimen (cat. no. 6340)
		Canis lupus familiaris	Domestic dog	USNTC (RML116166); NVSL records (1989); this study
		Vulpes vulpes	Red fox	This study (USNMENT1786486)
		Urocyon cinereoargenteus	Gray fox	This study (DMNH 2024.MOL.012-31)
		Felis catus	Domestic cat	This study (USNMENT1786485)
		Homo sapiens	Human	DCPH-A records (1998-2007, 2010-2011, 2013, 2015-2019); this study
		Cervus nippon	Sika deer	This study
		Odocoileus virginianus	White-tailed deer	Wolfe et al. 1994; this study (USNMENT1512907)
		Sylvilagus floridanus	Eastern cottontail	This study (DMNH # 2024.MOL.012-30)
		Peromyscus leucopus	White-footed mouse	This study (USNMENT1786493)
		Sciurus carolinensis	Eastern gray squirrel	This study (DMNH 2024.MOL.012-29)
		Tamias striatus	Eastern chipmunk	This study
		Plestiodon fasciatus (L.)	Common five-lined skink	This study
		Vireo olivaceus (L.)	Red-eyed Vireo	Adalsteinsson 2016
		Cyanocitta cristata (L.)	Blue Jay	Adalsteinsson 2016
		Baeolophus bicolor (L.)	Tufted Titmouse	Adalsteinsson 2016
		Hylocichla mustelina (Gmelin)	Wood Thrush	DMNH specimen (2008); Adalsteinsson 2016
		Catharus fuscescens (Stephens)	Veery	Adalsteinsson 2016
		Catharus ustulatus (Nuttall)	Swainson’s Thrush	SCWDS records (2018)
		Turdus migratorius	American Robin	Adalsteinsson 2016
		Dumetella carolinensis	Gray Catbird	Adalsteinsson 2016
		Toxostoma rufum	Brown Thrasher	DMNH specimen (2023)
		Thryothorus ludovicianus (Latham)	Carolina Wren	Adalsteinsson 2016
		Troglodytes aedon Vieillot	House Wren	Adalsteinsson 2016
		Cardinalis cardinalis	Northern Cardinal	Adalsteinsson 2016
		Spizella pusilla	Field Sparrow	This study
		Pipilo erythrophthalmus	Eastern Towhee	Adalsteinsson 2016
		Melospiza melodia	Song Sparrow	DMNH specimen (2018)
		Seiurus aurocapilla	Ovenbird	Adalsteinsson 2016
Ixodes texanus	Raccoon tick	Procyon lotor	Raccoon	USNTC (RML33546); Mellott and Connell 1965; this study (USNMENT1786487)
Rhipicephalus sanguineus	Brown dog tick	Canis lupus familiaris	Domestic dog	MacCreary 1945, Mellott and Connell 1965; NVSL records (1962, 1964, 1967); this study (USNMENT1786488)

Family Argasidae Murray: Genus Alectorobius Pocock: Alectorobius kelleyi (Cooley and Kohls, 1941), bat tick: = Carios kelleyi, Ornithodoros kelleyi

Alectorobius kelleyi, previously unreported in Delaware, was first detected in March 2023 in Newark, New Castle County, in a residence; additional specimens were collected at the same location in August and September 2023. Although only 3 specimens have been collected to date, which is not enough to determine establishment, A. kelleyi is established in all neighboring states (Pennsylvania, Maryland, and New Jersey; Cooley and Kohls 1944, Anastos and Clifford 1956, Occi et al. 2020) and likely in Delaware as well. Observations on iNaturalist indicate that it has been present in Delaware since at least 2021. Alectorobius kelleyi is broadly distributed across North and Central America (Nadolny et al. 2021) and usually feeds on bats, with Eptesicus fuscus (Palisot de Beauvois) noted as a preferred host species, although it has been reported biting humans (Vargas 1984, Walker et al. 1998) and dogs (Canis lupus familiaris (L.); Maestas 2019, Sullivan et al 2022). Removal or exclusion of resident bats from buildings can prompt bat ticks to seek other hosts, explaining bites on non-chiropteran species (Sullivan et al. 2022).

As a rule, humans infrequently encounter soft ticks because the latter are nidicolous, living in the nests or roosts of their hosts as opposed to questing for hosts on vegetation, and A. kelleyi is no exception (Sonenshine and Anastos 1960). Although it seldom bites humans, this species merits further investigation for its potential role as a reservoir of pathogenic agents. Alectorobius kelleyi ticks have tested positive for Borrelia, Bartonella henselae (Loftis et al. 2005), Candidatus Borrelia johnsonii (Schwan et al. 2009), and several Rickettsia species (Loftis et al. 2005, Nadolny et al. 2021, Occi et al 2023). However, this tick’s ability to vector these agents remains unestablished. Bites from A. kelleyi are associated with lymphadenopathy, malaise, fever, fatigue, and weight loss (Gill et al. 2004).

Genus Argas Latreille: Argas sp. [subgenus Persicargas]

Only one Argas sp. specimen has been collected in Delaware to date. The specimen was an adult male found crawling on a person in Kent County in June 2021. The specimen was identified morphologically as Argas persicus (Oken, 1818), the fowl tick or Persian fowl tick, based on the peripheral ring of large, rectangular cells on the dorsum, and the suture line between the dorsal and ventral surfaces of the idiosoma. However, DNA barcoding results (Egizi and Kennedy, unpublished data) indicate a potentially undescribed species in the Persicargas genus most closely related to Argas giganteus (Kohls and Clifford, 1968) specimens taken from raptors in Arizona (Latas et al. 2020). Of note, the collector of the specimen we examined had no recent travel history or contact with poultry. The collector did report spending time at a nature center that harbors occupied Barn Swallow (Hirundo rustica) nests on its outside walls during the summer months; however, subsequent examination of nests and dry-ice trapping at the nature center did not yield additional specimens.

Argas giganteus is a neotropical species primarily known to feed on small passerines. Records from the southwestern US indicate larvae may remain attached to hosts long enough to be transported, eg from Mexico into the United States, though transport from Arizona to Delaware seems unlikely. In Arizona, Argas giganteus was associated with paralysis and a subset of recovered ticks were infected with Rickettsia hoogstraalii and a species of relapsing fever Borrelia (Latas et al. 2020).

Argas persicus is native to the Middle East but members of its species group are distributed worldwide as pests of domestic poultry (Estrada-Peña et al. 2017) and vectors of Borrelia anserina and Aegyptianella pullorum (Gothe et al. 1981). The poultry industry is an important contributor to Delaware’s economy (USDA/NASS 2022), highlighting the need for added surveillance for A. persicus. Although A. persicus is not considered a human biter (Hoogstraal 1985), further investigation regarding the medical importance of the species detected in Delaware is warranted.

Argas persicus has been collected in Maryland and Pennsylvania, and MacCreary (1945) predicted that “[t]he fowl tick or blue bug, Argas persicus (Oken) which, up to the present time, has not been reported from [Delaware] will in all probability become established.”

Collection of additional Argas sp. specimens from Delaware and/or the mid-Atlantic region, with subsequent morphological examination and DNA barcoding, will be needed to resolve which species should be included in Delaware’s tick fauna.

Family Ixodidae Banks: Genus Amblyomma Koch: Amblyomma americanum (Linnaeus, 1758), lone star tick, turkey tick

Amblyomma americanum was first reported in Delaware by MacCreary (1945), with one specimen collected from a man in New Castle County in June 1939; it was established by 1999, with 23 Delaware specimens sent to the DCPH-A MilTick (Military Tick Identification/Infection Confirmation Kit) program for pathogen testing that year. Today, it ranks as the most commonly encountered tick species in the state (Kennedy and Marshall 2021). It was once predominantly found in the southeastern United States; however, its range continues to expand, and it is now found from Florida to Maine and as far west as central Texas and eastern Nebraska (Centers for Disease Control and Prevention 2018). This species is abundant statewide in all 3 counties, reaching higher densities in Kent and Sussex Counties than in New Castle County. In Delaware, larval density peaks between July and August, nymphal density between May and July, and adult density between April and June.

Amblyomma americanum is considered an aggressive tick species with generalist feeding tendencies. All postembryonic life stages will bite humans. It is medically significant as a vector of at least 3 agents of ehrlichiosis (Ehrlichia chaffeensis, Ehrlichia ewingii, and the unnamed agent of “Panola Mountain” ehrlichiosis) as well as Francisella tularensis (the causative agent of tularemia), Tacaribe virus, Heartland virus, and Bourbon virus (Killmaster et al. 2014). The lone star tick is also associated with southern tick-associated rash illness (STARI), of uncertain etiology, and the mammalian meat allergy also known as alpha-gal syndrome (Commins et al. 2016). Some authors (eg Cohen et al. 2009, Berrada et al. 2011) consider A. americanum a vector of spotted fever group rickettsiae. Not all these diseases have been reported in Delaware to date, but Delaware ranked among the top 3 states for incidence of both E. chaffeensis and E. ewingii in 2008-2012 (Heitman et al. 2016); field-collected Delaware ticks have tested positive for both pathogens (Buoni 2023).

White-tailed deer are a principal host species for A. americanum as well as a reservoir for Ehrlichia spp. Lone star ticks carry Theileria spp. parasites and parasitemia may contribute to deer mortality (Haus et al. 2018). This species also presents veterinary concerns in companion animals, serving as a vector of the agents of tularemia and feline cytauxzoonosis (Reichard et al. 2010).

Amblyomma maculatum Koch, 1844, Gulf Coast tick

This species was first collected in Delaware in 1939 (MacCreary 1945) but was not considered established until much later. Only one specimen had been collected at that time and was speculated to have been introduced by a migratory bird. By 2013, it was established in Kent County (Florin et al. 2014), and by 2019 in all 3 counties, with highest numbers collected in Sussex County (Maestas et al. 2020a). As its common name suggests, this species was historically found near the Gulf Coast and other Atlantic coastal areas, but it continues to expand into other parts of the United States, as far north as Connecticut (Molaei et al. 2021). Immatures are infrequently collected in Delaware, with larvae appearing between August and October and nymphs between May and September. Adult density in Delaware peaks from May to July.

Amblyomma maculatum is a vector of Rickettsia parkeri, the causative agent of Tidewater spotted fever (Paddock et al. 2004), and the first account of A. maculatum infected with R. parkeri in Delaware was from an adult female specimen collected at Bombay Hook National Wildlife Refuge in 2012 (Florin et al. 2013). The bite of A. maculatum has also been shown to cause tick paralysis, but removal of the tick rapidly relieves symptoms in patients (Paffenbarger 1951, Espinoza-Gomez et al. 2011). It is also a known vector of Hepatozoon americanum, the agent of hepatozoonosis in dogs, and A. maculatum infestations can cause anemia and gotch ear in livestock (Ewing and Panciera 2003).

Genus Dermacentor Koch: Dermacentor albipictus (Packard, 1869), winter tick: = D. nigrolineatus (Packard, 1869); syn. by Ernst and Gladney 1975

The winter tick Dermacentor albipictus was first reported in Delaware by Wolfe et al. (1994), who collected 484 specimens from white-tailed deer in November 1988. The distribution of D. albipictus is broad, extending from Florida to Canada and west to California (Leo 2012), and it is established statewide in all 3 Delaware counties. It typically only quests for a host during the larval stage; thus, nymphs and adults are only sporadically collected by flagging and dragging. Questing larval density in Delaware peaks in October and November.

Dermacentor albipictus typically feeds on cervids. It is a one-host tick and will remain on the same host for about 6 mo until adulthood (Calvente et al. 2020). We collected larvae, nymphs, and adults from hunter-harvested white-tailed deer in November and questing larvae from vegetation in each month from September through January.

While D. albipictus is the putative vector of Babesia duncani in the western United States (Swei et al. 2019), it is generally considered more important from a veterinary than a medical standpoint. In cervids, large infestations of this species are associated with anemia, hair loss, weight loss, and mortality, amplified by warm winters and early spring snowmelt (Calvente et al. 2020). Delaware’s only cervid species (white-tailed deer and sika deer) are not considered particularly at risk. It can also cause tick paralysis (Gothe et al. 1979).

Dermacentor variabilis (Say, 1821), American dog tick, wood tick

The first report of D. variabilis in Delaware was by MacCreary (1945), and records in the USNTC date to 1940. Climate change models predict a continuing westward and northward spread of this species, with potential for disease expansion as well (Boorgula et al. 2020). This species is established statewide in all 3 counties. In Delaware, questing larvae are typically collected from July to October; nymphs are rarely collected. Adult density peaks between May and July.

In immature stages, D. variabilis will often feed on rodents, but as adults, they are more selective toward canids. Other hosts include cervids, livestock, and humans (Bishopp and Trembley 1945).

Dermacentor variabilis is one of the principal ticks of public health importance in the United States for humans, wildlife, and domestic animals, as it vectors Rickettsia rickettsii, Francisella tularensis, Coxiella burnetii, and Anaplasma spp., the causative agents of Rocky Mountain spotted fever, tularemia, Q-fever, and anaplasmosis, respectively (de la Fuente et al. 2008). It is also associated with tick paralysis (McCue et al. 1948, Trumpp et al. 2019).

Genus Haemaphysalis Koch: Haemaphysalis leporispalustris (Packard, 1869), rabbit tick

The first report of H. leporispalustris in Delaware was by MacCreary (1945). This species has a wide distribution, extending from Alaska to Argentina (Burgdorfer 1969), and is established statewide in all 3 Delaware counties. In Delaware, larval density peaks between August and October and nymphal density between April and June; adults have rarely been collected.

Adults of this tick are highly host-specific, feeding primarily on rabbits, but immature stages will also feed on rodents and birds, particularly ground-dwelling birds such as the Ruffed Grouse (Bonasa umbellus (L.)) (Burgdorfer 1969).

As a species of moderate medical importance to humans, H. leporispalustris is responsible for the enzootic transmission of Francisella tularensis and Rickettsia spp. within rabbit and rodent populations. Rickettsia felis, the causative agent of cat flea typhus, was also found in a small sample of larvae, indicating the potential for transovarial transmission of this pathogen (Roth et al. 2016).

Haemaphysalis longicornis Neumann, 1901, longhorned tick, Asian longhorned tick, bush tick, cattle tick, Australian-Northeast Asian haemaphysalid

Haemaphysalis longicornis was first detected in the United States in 2017 on a New Jersey sheep farm (Rainey et al. 2018), and archival specimens of this species in the United States have been found dating to 2010 (Beard et al. 2018). The first detection of this species in Delaware was in 2019 in New Castle and Kent Counties (Maestas et al. 2020b); it is now established statewide. In Delaware, larval density peaks from August through October, nymphal density from May through July, and adult density in June and July.

This species is notable for its ability to demonstrate both bisexual and parthenogenetic reproductive strategies. In Delaware, as seen elsewhere in the United States, only females have been encountered. Parthenogenetic females can produce high numbers of offspring that lead to extremely high host infestations (Beard et al. 2018).

The medical significance of H. longicornis in the United States requires further investigation. In its native range and in other areas where it has been introduced, this species transmits severe fever with thrombocytopenia syndrome virus, leading to human hemorrhagic fever (Luo et al. 2015), and it has been found infected with R. japonica, the causative agent of Japanese spotted rickettsiosis (Tabara et al. 2011). In North America, its public health impact has thus far been limited. Importantly, this species cannot vector Borrelia burgdorferi (Breuner et al. 2020), Anaplasma phagocytophilum (Levin et al. 2021), or Francisella tularensis (Tully and Huntley 2020); however, in a laboratory setting, it can transmit Rickettsia rickettsii (Stanley et al. 2020), Powassan virus (Raney et al. 2022a), and Heartland virus (Raney et al. 2022b). Cumbie et al. (2022) detected Bourbon virus in field-collected H. longicornis in Virginia, and Herb et al. (2023) detected several species of Babesia in field-collected H. longicornis in New Jersey, including Babesia microti S837, a close relative of the agent of human babesiosis.

Haemaphysalis longicornis is a species of veterinary concern as it vectors Theileria orientalis, a protozoan parasite that causes theileriosis in cattle (Bos taurus L.), and this transmission cycle is under way in the United States (Dinkel et al. 2021). It does not vector Babesia bovis, an agent of cattle fever (Poh et al. 2024). Large aggregations on ungulate hosts are associated with reduced growth and anemia (Neilson and Mossman 1982), and high infestations can cause economic damage to hides as well as decreased dairy production (Perera et al. 2014).

While humans are not often a host species, reports of human bites in the United States have occurred (e.g., Wormser et al. 2020) and we have several records of human bites in Delaware.

Genus Ixodes Latreille: Ixodes banksi Bishopp, 1911, beaver tick

Ixodes banksi was first detected in Delaware in April 2023 on an American beaver in Kent County. A single nymph was removed from the beaver’s ear canal and barcoded with corresponding cox1 sequence available in GenBank (accession number OR413512). In November 2024, an additional 100 nymphs were collected from 3 beavers in New Castle County, thus meeting CDC criteria for establishment in Delaware. Ixodes banksi is infrequently collected throughout its range, but records exist from Arkansas, Michigan, Wisconsin, and Ontario (Hays and Lawrence 1957) as well as Alabama (Cooney and Hays 1972), Connecticut (Anderson and Magnarelli 1980), Missouri (Kollars et al. 1995), and Virginia (Robbins 2024).

Ixodes banksi is known to feed on beavers, muskrats (Ondatra zibethicus (L.)), and otters (Lontra canadensis (Schreber)) (Hays and Lawrence 1957). Reports from coyotes (Canis latrans Say) and skunks (Cooley and Kohls 1945) were determined to be the closely related I. cookei (Gregson 1956), and a report from a raccoon (Randolph and Eads 1946) needs confirmation. Occasional bites on humans have been reported (Walker et al. 1998, Merten and Durden 2000).

Ixodes brunneus Koch, 1844

Ixodes brunneus was first detected in Delaware in 2021 during routine tick surveillance efforts (dragging/flagging vegetation on public lands), as well as from a Northern Mockingbird (Mimus polyglottos (L.)) that was found killed by a window collision (Kennedy and Winter 2022). This species is established statewide in all 3 counties. Kennedy and Winter (2022) reported collecting only adults, but subsequent efforts have yielded nymphal specimens as well. In Delaware, nymphs have been collected from January through March, and adults from February through April.

Ixodes brunneus feeds almost exclusively on birds, specifically passerines (Keirans and Clifford 1978), with the result that it is uncommonly encountered by humans. For this reason, its public health significance is considered minimal. As an avian ectoparasite, it is associated with reduced eyesight (Thomas 1941) and tick paralysis (Luttrell et al. 1996).

Ixodes cookei Packard, 1869, groundhog tick, woodchuck tick, mustelid tick: = I. cruciarus Fitch 1872: = I. hexagonus var. longispinosus Neumann 1901: = I. hexagonus var. cookei Nuttall and Warburton 1911

The first report of this species in Delaware was by MacCreary (1945); however, records in the USNTC from a red fox in Kent Co. date to 1939. Recent collections of all motile stages, mostly from wildlife hosts, indicate a statewide distribution. Ixodes cookei is broadly distributed across the United States, from Maine to Florida and west to South Dakota (Keirans and Clifford 1978).

Common hosts for this species include mesomammals such as mustelids, groundhogs, foxes, and raccoons (Kollars and Oliver 2003, Ferreira et al. 2023).

Ixodes cookei is an infrequent human biter (Walker et al. 1998); however, it is the main species associated with Powassan virus lineage I in the United States (Main et al. 1979) and has recently been associated with lineage II (deer tick virus; Smith et al. 2018). It is considered a vector of Borrelia burgdorferi, albeit a far less important one than I. scapularis (Barker et al. 1993). Rickettsia spp. have also been isolated from I. cookei, but its ability to transmit them is uncertain (Magnarelli and Swihart 1991). Xu et al. (2018) reported an Ehrlichia muris-like agent in I. cookei from Maine and New York.

Ixodes dentatus Marx, 1899

This species was first reported in Delaware by MacCreary (1945); however, records in the USNTC from an Eastern cottontail (Sylvilagus floridanus (J.A. Allen)) in New Castle County date to 1939. Its distribution spans the eastern and central United States (Keirans and Clifford 1978). Ixodes dentatus is established statewide in all 3 Delaware counties but has to date only been collected in low numbers.

Keirans and Clifford (1978) note that this species primarily feeds on rabbits and birds. MacCreary (1945) reported one specimen from a “meadow mouse” (= meadow vole, Microtus pennsylvanicus (Ord)).

Although it is not a frequent human biter, I. dentatus deserves recognition as a carrier of Borrelia miyamotoi (Hamer et al. 2012), an agent of relapsing fever, and may help to maintain Borrelia burgdorferi in an enzootic cycle (Anderson et al. 1989). It is also a vector of Borrelia andersonii, a genospecies within B. burgdorferi sensu lato (Oliver et al. 2003). Anaplasma phagocytophilum, the agent of anaplasmosis, has been detected in I. dentatus collected in Canada and South Carolina (Ogden et al. 2008, Nelder et al. 2009).

Ixodes keiransi Beati, Nava, Venzal, and Guglielmone, 2023: = Ixodes affinis Neumann, 1899

Ixodes keiransi was first detected in Delaware in April 2023 during routine tick surveillance efforts (flagging vegetation on public lands) in Kent County; however, examination of older material revealed additional, previously misidentified specimens, the earliest of which was collected in April 2021 in New Castle County. To date, more than 25 specimens, including larvae, nymphs, and adults, have been collected in Delaware, and collections in each county indicate a statewide distribution. One specimen, a female collected from the environment in Kent Co. in April 2023, was barcoded with corresponding cox1 sequence available in GenBank (Accession Number OR413511). The occurrence of I. keiransi in Delaware is a predictable outcome of its recent northward expansion into the Mid-Atlantic region (Nadolny and Gaff 2018).

This species is not known to bite humans, although it helps to maintain Borrelia burgdorferi bacteria in an enzootic cycle in wildlife hosts (Oliver et al. 2003). Wildlife hosts include eastern cottontail (Nelder and Reeves 2005), white-tailed deer, bobcat (Lynx rufus (Schreber)), and raccoons (Durden and Keirans 1996). Additionally, there are records of this species feeding on domestic dogs (Durden and Keirans 1996, Wells et al. 2004, Saleh et al. 2019).

Ixodes marxi Banks, 1908, squirrel tick

Ixodes marxi was first reported in Delaware by MacCreary (1945); however, specimens in the USNTC date to 1939. Notably, this species has not been documented in Delaware in recent years; to date, the state tick program has not collected any specimens of this species. This may reflect a lack of sampling effort targeted at its preferred host species (squirrels; Kolonin 2007).

As a specialist on squirrels, Ixodes marxi rarely bites humans; however, it helps to maintain Powassan virus in an enzootic cycle with squirrels (Hassett and Thangamani 2021).

Ixodes minor Neumann, 1902 (Uncertain record)

The report of I. minor in Delaware is of particular interest because its known distribution is restricted to the southeastern United States (Florida, Georgia, and South Carolina; Banks et al. 1998) and an isolated population in California (Foley et al. 2014). Adalsteinsson (2016) reported one I. minor larva on an Eastern Towhee (Pipilo erythrophthalmus (L.)) and one larva on a Northern Cardinal (Cardinalis cardinalis (L.)) in New Castle County. These 2 specimens do not meet the minimum criteria for establishment in Delaware. Northern Cardinals do not migrate, and Eastern Towhees are considered short-distance migrants, with Delaware at the northern edge of the wintering range (Cornell Lab of Ornithology 2024), so the presence of I. minor larvae on these species in Delaware may indicate the existence of a local population. However, given that the specimens in question were identified using morphological methods without molecular confirmation, we consider this an uncertain record.

In the southeastern United States, I. minor helps maintain Borrelia carolinensis in an enzootic cycle, but its pathogenicity to humans remains unsettled (Foley et al. 2014).

Ixodes muris Bishopp and Smith, 1937, mouse tick (Uncertain record)

Three slide-mounted nymphal Ixodes ticks were discovered in the UDCC in 2022. The slides were labeled “Ixodes muris” collected in Newark, New Castle Co. between 1990-1992. Follow-up correspondence with the collector indicated that they were removed from human hosts. All 3 specimens were of poor quality and could not be keyed to species; features such as the lateral carinae and hypostomal apex were not discernible. Ixodes muris has been reported from Maryland and Pennsylvania (Durden and Keirans 1996), so its presence in Delaware would not be unexpected. It is considered a frequent parasite of humans (Guglielmone and Robbins 2018 and references within), making this record plausible, but unverifiable. We therefore consider this an uncertain record.

Ixodes muris can vector Borrelia burgdorferi, the causative agent of Lyme disease, but is not a highly competent vector (Dolan et al. 2000).

Ixodes scapularis Say 1821, blacklegged tick, deer tick: = Ixodes dammini Spielman, Clifford, Piesman and Corwin 1979; syn. by Oliver et al. 1993

The earliest report of I. scapularis in Delaware was in 1983 by Burgdorfer and Keirans (Burgdorfer and Keirans 1983); specimens in the USNTC date to 1982. It was established statewide by 1988 (Wolfe et al. 1994). The distribution of this species is rapidly expanding, and as of 2016, nearly half the counties in the United States had reported this species (Eisen et al. 2016). Ixodes scapularis is established statewide in all 3 Delaware counties. Larval density peaks from July through September, nymphal density from May through July, and adult density in November and March.

Host species of this tick vary by latitude and life stage. As adults, I. scapularis will seek out large-bodied hosts, such as white-tailed deer and dogs. Small mammals, such as mice and other rodents, and birds are typical hosts for immature stages (Keirans et al. 1996). White-footed mice (Peromyscus leucopus (Rafinesque)) have long been acknowledged as an important host for blacklegged ticks, and a reservoir of Borrelia burgdorferi bacteria (Levine et al. 1985).

Ixodes scapularis is arguably the most medically important tick species in the United States because it transmits at least 7 pathogens that can cause disease in humans. These include Borrelia burgdorferi, the causative agent of Lyme disease, which is responsible for an estimated 300,000 human cases every year (Marques 2018). Ixodes scapularis can also transmit B. mayonii, Anaplasma phagocytophilum, Babesia microti, Powassan virus (lineage II: deer tick virus), Ehrlichia muris eauclairensis, and Borrelia miyamotoi, the causative agents of Borrelia mayonii disease, anaplasmosis, babesiosis, Powassan virus disease, ehrlichiosis, and tick-borne relapsing fever, respectively (Aliota et al. 2014, Dolan et al. 2016, Tokarz et al. 2017). Importantly, while some pathogens cannot be transmitted from a tick to a host until the tick has been attached for an average of 24 h, deer tick virus can be transmitted in as little as 15 min of tick attachment (Ebel and Kramer 2004). In Delaware, field-collected I. scapularis ticks have tested positive for B. burgdorferi and Anaplasma phagocytophilum since 1998 (Curran et al. 2000); more recently, they have tested positive for Babesia microti as well (Buoni 2023).

Ixodes texanus Banks, 1909, raccoon tick

This species was first reported in Delaware by Darsie and Anastos (1957) from specimens collected in Sussex County in 1953 to 1954. With additional recent collections from New Castle and Kent Counties, we consider this species established statewide.

While all Delaware records of this species were collected from raccoons or the environment, Ixodes texanus is known to occasionally parasitize humans and domestic animals. Borrelia burgdorferi and Rickettsia rickettsii have been isolated from this species (Hamer et al. 2010). Additionally, it has been implicated as a vector of Babesia lotori, agent of raccoon babesiosis (Anderson et al. 1981).

Genus Rhipicephalus Koch: Rhipicephalus sanguineus (Latreille, 1806), brown dog tick, kennel tick, crib tick, pan-tropical dog tick

As currently understood, the cosmopolitan R. sanguineus complex comprises 2 clearly defined groups: R. sanguineus sensu stricto, which is found in the Nearctic, Neotropical, and European Palearctic regions, and R. linnaei (Audouin, 1826), which is recognized as a member of the “tropical lineage” of R. sanguineus sensu lato and is known from southern Europe, Africa, East and Southeast Asia, parts of Oceania, Australia, and the Western Hemisphere. Rhipicephalus sanguineus sensu stricto was redescribed morphologically and molecularly by Nava et al. (2018), who also selected a neotype from a French population, while comparable analyses of R. linnaei, together with designation of an Egyptian neotype, were published by Šlapeta et al. (2022). However, there are several closely related species in the R. sanguineus complex, and many populations of R. sanguineus sensu lato worldwide will likely be found to belong to R. sanguineus s.s. (Guglielmone et al. 2023). For the moment, it suffices to say that ticks belonging to the R. sanguineus complex are known from Delaware, having first been recorded in Wilmington in 1939, on a dog that had been shipped to Delaware from Georgia (MacCreary 1945).

Rhipicephalus sanguineus is a species of medical and veterinary concern. In the southwestern United States, it vectors Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, and in the Mediterranean region, this species vectors Rickettsia conorii, the agent of Boutonneuse fever; moreover, in Africa and Eurasia, this species can transmit Crimean-Congo hemorrhagic fever virus (Estrada-Peña and Jongejan 1999). Rhipicephalus sanguineus additionally vectors Ehrlichia canis (causative agent of canine ehrlichiosis), which typically affects dogs, although some reports (eg Sgroi et al. 2024) indicate it is pathogenic to humans as well. The brown dog tick vectors other agents of veterinary concern such as those causing canine babesiosis (Babesia vogeli and possibly B. conradae and B. gibsoni), spotted fever group rickettsiae (R. rickettsii and possibly R. massiliae, R. monacensis, R. montanensis, R. amblyommatis, and others) (Lineberry et al. 2022 and references within), and possibly Anaplasma platys (Ramos et al. 2014). Additionally, infestations are associated with anemia, abscesses, and tick paralysis in dogs (Gray et al. 2013 and references within).

Host preferences for this complex are mainly dogs, but R. sanguineus will bite humans. It has been nicknamed the “crib tick” because of its tendency to bite victims under 5 yr of age (Stromdahl et al. 2011). Warming global temperatures have been associated with an increase in the activity and aggressiveness of this species, increasing human risk (Tomassone et al. 2018). It is a nidicolous species, primarily associated with enclosed habitats, such as homes and dog kennels (Gray et al. 2013) and likely unable to survive winters outdoors in Delaware.

Ticks Intercepted in Delaware

According to NVSL records, the following exotic ticks were detected upon entry into Delaware via Dover Air Force Base:

Hyalomma excavatum Koch, 1844: on baggage, 1984

Amblyomma cajennense (Fabricius, 1787), cayenne tick: on plant material, 1988; on plantain, 1989; on banana (Musa sp.), 1990. The taxonomic status of these specimens is unclear, A. cajennense sensu lato having subsequently been divided among 6 species (Nava et al. 2014).

Discussion

We report 15 established Ixodidae species in Delaware, 2 additional Ixodidae and 2 Argasidae species that are still unconfirmed due to the small number of specimens collected, and report specimens of 2 species that were intercepted in quarantine zones. Most of these tick species are not considered important for human health because they are rarely encountered by people, but Ixodes scapularis, Amblyomma americanum, Dermacentor variabilis, and Amblyomma maculatum are of considerable medical concern due to high infection rates with human pathogens and high rates of human-tick encounters (Eisen 2020).

Based on available voucher specimens and recent collections, the state of New Jersey, directly north of Delaware, has 14 established species of Ixodidae (9 indigenous, 2 exotic) (Occi et al. 2019, Ferreira et al. 2023, Musnoff et al. 2024, Narvaez et al. 2024). Additionally, the argasid tick Alectorobius kelleyi was found to be established in New Jersey (Occi et al. 2020). As expected, based on geographic proximity, the tick faunas of New Jersey and Delaware are similar.

With continued surveillance efforts, we expect that additional tick species will be detected in Delaware. For example, Ixodes kingi Bishopp has been reported from neighboring Maryland, although this species appears to be more common in western and central North America (Lindquist et al. 2016). Ixodes angustus Neumann has been reported from western Pennsylvania, a cool, elevated, and relatively moist region that typifies this species’ habitat throughout its range; it is therefore less likely to be found in Delaware (Robbins and Keirans 1992). Haemaphysalis chordeilis (Packard), which chiefly infests birds, has been spottily reported across North America, and though rarely collected in recent years (Egizi and Maestas 2022) it could be reported from Delaware in the future.

Understanding which tick species occur in each area, when they are most likely to be encountered, and which host species they feed on is a basic but important step in evaluating the risks they pose to humans, livestock and companion animals, and wildlife. A robust tick surveillance program should incorporate a variety of active and passive surveillance methods, as described above, to be best poised to detect new tick species, host records, and range expansions. We recommend that other jurisdictions develop checklists of their tick faunas and update them accordingly through ongoing surveillance efforts.

Dedication: This work is dedicated to the memory of Ralph P. Eckerlin (1938-2024), parasitologist par excellence, preeminent expert on Siphonaptera, and esteemed friend and mentor to many.

Disclaimer

All material in this paper has been reviewed by the Walter Reed Army Institute of Research. There is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the true views of the U.S. Department of the Army or the Department of Defense.

Author contributions

Ashley Kennedy (Conceptualization [Lead], Data curation [Equal], Investigation [Lead], Methodology [Equal], Project administration [Lead], Resources [Lead], Supervision [Lead], Writing—original draft [Lead], Writing—review & editing [Equal]), Sierra Redus (Data curation [Equal], Investigation [Equal], Methodology [Equal], Writing—review & editing [Equal]), Wil Winter (Investigation [Equal], Methodology [Equal], Writing—review & editing [Equal]), Jeffrey Newcomer (Investigation [Equal], Methodology [Equal], Resources [Equal], Writing—review & editing [Supporting]), Andrea Egizi (Investigation [Supporting], Methodology [Supporting], Writing—review & editing [Equal]), Dina Fonseca (Investigation [Supporting], Methodology [Supporting], Writing—review & editing [Equal]), James Occi (Investigation [Supporting], Methodology [Supporting], Writing—review & editing [Equal]), and Richard Robbins (Investigation [Equal], Methodology [Equal], Writing—original draft [Equal], Writing—review & editing [Equal])

Funding

The molecular identification of Alectorobius kelleyi was supported by a United States Department of Agriculture National Institute of Food and Agriculture Multistate Grant, NE1943 to DMF.

Conflicts of interest. None declared.