External Parasites of Pennsylvania Deer

Background Information

White-tailed deer harbor a number of external parasites that hunters may come in contact with when dressing and processing harvested deer. Some, such as blacklegged ticks and deer keds, can bite hunters and may transmit pathogens. Others, such as winter ticks, rarely bite humans but may cause concern due to their abundance on deer. 

Blacklegged tick

Scientific name: Ixodes scapularis

Figure 1. Adult female (left) and male (right) blacklegged ticks. Note the smaller scutum of the female. Photographs by Erika Machtinger, Penn State.

Identification

Blacklegged ticks are dark brown to nearly black. In females, the scutum (the hard shield on the dorsum of the tick is short and dark brown, while the soft part of the idiosoma (abdomen) is usually red, although this may be difficult to see in ticks that have fed and are engorged with blood (Figure 1). In males, the scutum is larger and covers most of the idiosoma, so the tick appears entirely dark brown (Figure 1). Blacklegged ticks move slowly.

Distribution

Ixodes scapularis are found throughout the eastern United States and in parts of the northern Midwest in wooded, brushy locations as well as grassy edge habitat. While they were less widespread historically, the range of this species has been expanding in recent years and they can now be found throughout Pennsylvania.

Hosts

Blacklegged tick larvae preferentially feed on small mammals such as mice and chipmunks and occasionally birds; nymphs also feed on small mammals and birds, as well as a range of medium and large mammals like raccoons, deer, and black bears. Adult blacklegged ticks feed on larger mammals, with some preference for white-tailed deer. However, any stage is capable of biting and feeding on humans.

Activity Period

Adult ticks are present in the fall, throughout the winter, and in early spring. During the winter, adult ticks can be active and seek hosts any day when temperatures are above freezing. They can be found on deer during this time, often in abundance, and can climb from a deer to a hunter regardless of the air temperature. Larval ticks are typically present during the late summer and nymphs during the late spring and through the summer.

Diseases

Blacklegged ticks are best known as the vector of the pathogens that cause Lyme disease, but have also been known to vector other pathogens including Anaplasma spp. and Babesia spp. which can cause anaplasmosis and babesiosis, respectively. While there is still some debate, blacklegged ticks typically need to feed for 24 hours before Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted. However, another pathogen, Powassan virus, can be transmitted in as little as 15 minutes. Because ticks need to feed from a host infected with pathogens to be able to transmit those pathogens to humans or other animals, only nymphs and adult ticks spread the pathogen. In Pennsylvania, 20–40% of blacklegged ticks test positive for B. burgdorferi depending on location.

Notes

This tick is often called the "deer tick." However, because deer are the preferred host only during the adult stage, this name is not reflective of their entire biology. Instead, "blacklegged tick" is the preferred common name, as it better reflects the nature of the tick. 

Winter tick

 Dermacentor albipictus

Figure 2. Winter ticks. Female winter ticks (left) have a small, dark scutum with bolder white areas on the idiosoma. Male winter ticks (center) have a large scutum so most of the idiosoma appears dark. Some individuals (center) lack a reticulated pattern and are plain and light brown in color. Left photograph by Jason J. Dombroskie via iNaturalist, used under a CC BY-NC 4.0 license. Center photograph by Erika Machtinger, Penn State. Right photograph by Andrea Kautz via iNaturalist, used under a CC0 1.0 license.

Identification

Winter ticks have light brown legs and palps. The soft parts of the idiosoma, or abdomen, are dark brown, while the scutum, which is the hard plate that covers the idiosoma, often has ornate white, net-like patterning called reticulations. Females have a small scutum so the dark brown area is proportionally larger and the reticulated pattern can be difficult to see, while males have a large scutum and an obvious reticulated pattern (Figure 2). Some winter ticks are brown and inornate, that is, they lack the white reticulated patterning. Winter ticks have festoons, which are square or rectangular impressions, along the rear of the idiosoma.

Distribution

Winter ticks are found throughout North America, including all of Pennsylvania.

Hosts

Winter ticks are one-host ticks that feed on cervids. Cervids are members of the deer family like elk and white-tailed deer, while "one host" means ticks do not leave the host between life stages (larva, nymph, adult). So the only time that winter ticks are usually encountered are when they are on a deer, elk, or other cervid.

Activity Period

Larval ticks hatch in late summer, after which they climb onto hosts, feed, and molt into nymphs. Nymphs undergo diapause (a waiting/resting period) before molting into adults in mid-winter. Adults feed and mate on the host. Females drop off the host in late winter, lay eggs, and die. Depending on the hunting season and time of year, hunters may encounter nymphs and/or adult ticks on deer.

Diseases

Because winter ticks do not leave the host between life stages, they do not have the opportunity to acquire or transmit pathogens. However, some animals, especially those that are sick or injured, can have large winter tick infestations that lower their quality of life (Figure 3). Winter ticks populations can build to such high numbers on moose in Maine that they can kill heavily-infested animals. Such heavy infestations do not usually occur in Pennsylvania, although there is one documented case of a winter tick infestation killing an elk calf.

Figure 4. Winter tick infestation on a white-tailed deer. Photograph by Erika Matchinger, Penn State.

Look-alike Species

Winter ticks are closely related to American dog ticks (Dermacentor variabilis), which are three-host ticks (each life stage feeds on a different host) that are occasionally found on deer. Because they feed on different hosts during each life stage, American dog ticks are capable of vectoring various pathogens, including Rocky Mountain spotted fever and tularemia. American dog ticks are typically active during the summer, but may be found during the winter on warm days. They can be distinguished from winter ticks based on the shape of the spiracular plate, which is located on the side of the tick and requires magnification to observe. The spiracular plate of winter ticks is round, while American dog ticks have an obvious projection. 

Asian longhorned tick

Haemaphysalis longicornis

Figure 4. Asian longhorned tick. Photograph by Erika Machtinger, Penn State.

Identification

Asian longhorned ticks are uniformly brown (Figure 4). They do not have white reticulations like winter ticks and lack festoons.

Distribution

Asian longhorned ticks are a recently introduced invasive species that were first discovered in New Jersey in 2017. Since then, they have been found patchily across the eastern United States, including twelve Pennsylvania counties (Figure 5). Given this rather disjunct distribution, it is likely that increased survey efforts will find them in other areas as well.

Hosts

Asian longhorned ticks preferentially feed on ungulates such as deer, cattle, horses, and goats. Infestations on these animals can be extremely high to the point of causing physical damage and allowing secondary infections to take hold. Only one human bite has been reported, despite some areas having extremely dense infestations of thousands of Asian longhorned ticks. While human bites are possible, Asian longhorned ticks will likely pose the greatest threat to wildlife and farm animals.

Activity Period

All Asian longhorned tick lifestages are active from the spring through the fall, although nymphs are most common in late spring and early summer and adults are most active from June to August. Archery and muzzleloader hunters may encounter Asian longhorned ticks in September and possibly October, while rifle and other late-season hunters are unlikely to find them.

Diseases

Given the lack of human bites, Asian longhorned ticks are not known to transmit pathogens to humans in North America. They may be able to vector pathogens to wildlife and farm animals as they are known to do so in other areas of the world, although transmission has not yet been recorded in the United States.

Look-alike species

Asian longhorned ticks may be confused with brown dog ticks (Rhipicephalus sanguineus), which have rarely been reported from deer (their preferred hosts are canids, such as foxes, coyotes, and domestic dogs). Asian longhorned ticks and brown dog ticks can be distinguished based on the shape of the palps and basis capitula: in Asian longhorned ticks, the basis capitula is rectangular and the palps extend laterally beyond it. In brown dog ticks, the basis capitula is pentagonal and extends laterally beyond the palps. These features are best viewed using magnification. 

European deer ked

 Lipoptena cervi

Figure 6. Adult deer keds emerge with wings (left). After they land on a host, they shed thier wings and the abdomen expands (right). Photographs by Erika Machtinger (left) and Michael Skvarla (right), Penn State.

Identification

European deer keds are light brown, flattened flies. Keds that have not yet found a host have wings and a small abdomen (Figure 6) and frequently land on humans by mistake. Keds that have landed on a host and fed have larger, expanded abdomens (Figure 6). The abdomen has 3-4 dark brown stripes that indicate the segmentation of the abdomen. The legs are sprawled out to the side. Wingless keds can move quickly and appear to "swim" through deer hair when found on host.

Distribution

European deer keds are native to Europe. They were introduced into North America in the late 1800s and were first recorded in New Hampshire. European deer keds have since spread throughout the Northeast as far south as Virginia and west into Ohio.

European deer keds are present across Pennsylvania except for the southeastern corner, where they are apparently absent or at least very rare (Figure 7). They are most common and abundant in the northern tier, including Potter and Tioga counties.

Three other species of deer keds are native to North America, including Neotropical deer keds in the Southeast and Texas, and two species in western North America.

Figure 7. Pennsylvania counties where deer keds have been found.

Hosts

Deer keds preferentially colonize cervids. In Pennsylvania, this includes wild white-tailed deer and elk, as well as captive individuals of other exotic species. However, winged keds are attracted to hosts by movement (rather than scents like many ticks and mosquitoes), so regularly land on and bite humans and dogs.

Activity Period

European deer keds mass emerge in the fall. Their flight distances are correlated to temperature, so they are most active and frequently encountered on warm days.

Diseases

A number of typically tick-borne pathogens have been found in deer keds, including Anaplasma phagocytophilum and Borrelia burgdorferi, which cause human granulocytic anaplasmosis and Lyme disease, respectively. However, those studies sequenced whole, wild-caught keds and it's not clear if the pathogens are in the keds or in the last blood meal from an infected host, or if keds are capable of transmitting pathogens to humans. Ongoing research at Penn State aims to address this lack of knowledge.

Natural History

European deer keds are long-lived and can be found on hosts in late summer, right up to the point that new keds emerge. Once new keds emerge, it is impossible to age them so it is possible that keds may live for more than a year. Larval deer keds develop internally in the mother and are fed by a special ked "milk" she secretes. Fully developed larvae are born and immediately pupate, after which they fall out of the hair of the host. They then wait in the leaf litter for up to 11 months to emerge the following fall. Because of this, areas where deer frequent can become ked "hot spots" that accumulate a lot of pupae and so have many adults when they emerge. It’s not currently clear if there are any environmental factors correlated with these "hot spots".

Prevention and control of ticks on people

Long-sleeved shirts and long pants tucked into socks also aid in preventing tick bites. Light-colored clothing helps to detect the dark-colored tick provided the wearer inspects for ticks intermittently. While a light-colored top layer may not always be practical while hunting, a light-colored under layer can still help you detect ticks when hunting is over.

Repellents such as DEET (N,N-Diethyl-meta-toluamide) offer considerable protection if applied to clothing and exposed skin. Another protective option is the application of Permanone™, an effective acaricide that contains the synthetic pyrethroid permethrin and is applied as a spray to clothing. It is not approved for use on skin. For more information, see the EPA Repellent Search Tool.

Blacklegged ticks climb up plants and grab onto passing animals or people, so hunters can decrease the risk of contacting ticks by walking down the middle of service roads, trails, and similar avenues.

Deer do not carry the pathogen that causes Lyme disease. For other game, like turkey, cooking destroys the bacteria and eliminates any danger of getting Lyme disease. There are no documented cases of transmission through handling or consuming hunted game with previously attached ticks.

Self-examination is recommended after spending time outdoors. If an embedded tick is found, it should be removed with fine tweezers by grasping the head and pulling with steady firm pressure. The tick should not be grabbed in the middle of its body because the gut contents may be expelled into the skin. The use of heat (lit match, cigarette, etc.), or petroleum jelly is not recommended to force the tick out. These methods will irritate the tick and may cause it to regurgitate its stomach contents into the individual, thereby increasing the possibility of infection.

If signs or symptoms of Lyme disease or other diseases manifest, seek immediate medical attention and alert your physician to the history of a tick bite.

Prevention and control of ticks on companion animals

Lyme disease and other tick-borne diseases also companion animals such as hunting dogs. For information on prevention and control in animals, please see the Penn State fact sheets on Protecting Companion Animals Against Ticks in Pennsylvania and Protecting Livestock Against Ticks in Pennsylvania.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

References and additional reading

CDC. Ticks. Accessed 3 February 2021.

Edwards, M. J., J. C. Russell, E. N. Davidson, T. Y. Yanushefski, B. L. Fleischman, R. O. Heist, J. G. Leep-Lazar, S. L. Stuppi, R. A. Esposito, and L. M. Suppan. 2019. A 4-year survey of the range of ticks and tick-borne pathogens in the Lehigh Valley Region of Eastern Pennsylvania. Journal of Medical Entomology, 56(4): 1122–1134. DOI.org/10.1093/jme/tjz043

Farone, T. S., E. R. Campagnolo, K. L. Mason, and C. L. Butler. 2018. Borrelia miyamotoi infection rate in black-legged ticks (Ixodes scapularis) recovered from heads of hunter-harvested white-tailed deer (Odocoileus virginianus) in Pennsylvania: A public health perspective. Journal of the Pennsylvania Academy of Science, 92(1): 11–12. DOI.org/10.5325/jpennacadscie.92.1.0001

Hutchinson, M. L., M. D. Strohecker, T. W. Simmons, A. D. Kyle, and M. W. Helwig. 2015. Prevalence rates of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae), Anaplasma phagocytophilum (Rickettsiales: Anaplasmataceae), and Babesia microti (Piroplasmida: Babesiidae) in host-seeking Ixodes scapularis (Acari: Ixodidae) from Pennsylvania. Journal of Medical Entomology, 52(4): 693–698. DOI.org/10.1093/jme/tjv037

Livengood, J. M. L. Hutchinson, N. Thirumalapura, and D. Tewari. 2020. Detection of Babesia, Borrelia, Anaplasma, and Rickettsia spp. in adult black-legged ticks (Ixodes scapularis) from Pennsylvania, United States, with a Luminex multiplex bead assay. Vector-borne and Zoonotic Diseases, 20(6): 406–411. DOI.org/10.1089/vbz.2019.2551

Pak, D., S. B. Jacobs, and J. M. Sakamoto. 2019. A 117-year retrospective analysis of Pennsylvania tick community dynamics. Parasites & Vectors, 12: 189. DOI.org/10.1186/s13071-019-3451-6