Deer Keds

Classification

Common name: European deer ked

 Scientific name: Lipoptena cervi

            Order: Diptera (flies)

            Family: Hippoboscidae (louse flies and keds)

            Genus: Lipoptena (deer keds)

Description

Deer keds are brown, flattened flies. When adults emerge, they have wings and fly to find a host (Figure 1). After they land on a host, they shed their wings and appear somewhat tick-like (Figure 2).

Figure 1. A winged European deer ked. Photograph by Marie Lou Legrand via iNaturalist, used under a CC BY-NC 4.0 Deed license.

Figure 2. A wingless European deer ked. Note the wing stubs that are visible on the thorax. After landing on a host and feeding, the abdomen expands, although not to the same degree as a tick when ticks engorge. Photograph by mistycal via iNaturalist, used under a CC BY-NC 4.0 Deed license.

Distribution

Four species of deer keds are found in North America (Figure 3). Three of these are native to the region: Neotropical deer keds (Lipoptena mazamae) are found in the southeastern United States south through Central and South America. In contrast, western deer keds (L. depressa) and Pacific deer keds (Neoloptena ferrisi) are found in western North America. A fourth species, European deer keds (L. cervi), are found in the northeastern United States and adjacent Canada and are the focus of this article.

Figure 3. Range of deer ked species in North America north of Mexico. Modified from Skvarla and Machtinger (2019) and Skvarla et al. (2020).

European deer keds are native to Eurasia, including almost all of Europe west across Russia. They were accidentally introduced into North America and were first found in New Hampshire and Pennsylvania in 1907. They have since spread throughout most of the Northeast, west into Ohio, and south into Virginia.

In Pennsylvania, European deer keds are most common and abundant in northern tier counties, particularly McKean, Potter, and Tioga counties, where many deer harbor large infestations. They are present but less abundant in central and western counties, where heavy infestations on deer are uncommon, and some deer lack keds. European deer keds are nearly absent from the southeastern quadrant of Pennsylvania, where we have found just a single ked despite sampling hundreds of deer.

Natural History and Behavior

Unlike most insects, larvae develop internally inside the mother ked and feed on a special "milk" she secretes. When fully mature, the larvae are "larviposited" and immediately pupate (like a cocoon). Pupae rest in soil and leaf litter for up to 11 months until they emerge as adults the following fall. Because they roll off the host randomly, deer ked pupae tend to accumulate in areas where deer congregate and spend a lot of time, such as bedding areas, which can become deer ked hotspots.

Adult European deer keds emerge from their pupa on warm days in the fall and immediately fly to a mammalian host. Once they land on a host, they shed their wings. Wing shedding enables keds to climb quickly through the hair but can make them look like "weird ticks." Deer keds prefer to feed on deer, elk, and other cervids and can live for at least a year on a host. Based on observations of related species, female European deer keds likely produce fewer than a dozen offspring.

European deer keds are usually found in wooded areas but sometimes fly up to 50 yards into open areas like fields and lawns. It’s not clear why they are restricted to forests, but is likely related to the habitat requirements of the pupae due to their long resting periods. That is, leaf litter likely buffers pupae from weather and temperature better than more open areas, so only the pupae that fall off deer in forests survive to emerge the following fall.

Because they are protected within the leaf litter, cold weather does not affect European deer ked pupae. One study found that dark-colored pupae that fall onto snow heat up enough from the sun to melt through snow, which protects them from wind and weather until the snow melts.

Unlike mosquitoes and some ticks, which use chemical cues like carbon dioxide to find their hosts, winged keds use movement. So, while they prefer to feed on deer, they will fly to a large moving object they can see, and frequently land on and bite people. Wingless keds can quickly crawl from a deer to a hunter, butcher, or anyone else who handles deer.

Impacts on Deer

Most deer have relatively low infestations; even heavily infested animals do not exhibit obvious impacts. These observations are supported by research on Neotropical deer keds in South Carolina, which found that ked infestations increased deer grooming but did not impact overall health.

In Scandinavia, European deer keds can become so abundant on moose that the moose develop alopecia, which is a partial or complete loss of the hair, and die during harsh winters. European deer keds have not been reported from moose in North America, and this phenomenon has not been observed on any North American deer or elk.

Pathogens

Because deer keds feed on blood and bite people, there have been concerns about pathogen transmission between animals and humans. In the last decade, half a dozen tick-borne pathogens have been found in deer keds, so this concern is not unreasonable. A recent study screened hundreds of European deer keds collected in Pennsylvania for pathogens. They reported that 8.8% of deer keds tested positive for Anaplasma phagocytophilum and 80% of keds from 30 of 31 counties tested positive for Bartonella schoenbuchensis. Anaplasma phagocytophilum causes human granulocytic anaplasmosis, which is a potentially deadly disease. It is not clear if B. schoenbuchensis causes human disease, but it has been suggested to be the cause of deer ked dermatitis in Europe.

However, while these pathogens were found in deer keds, it is unclear whether keds can transmit them to humans or animals through bites. Given this uncertainty, you should treat a ked bite like a tick bite and, if a deer ked bites you, talk to your doctor if you experience flu-like in the weeks after the bite.

Avoiding Bites

A recent study tested deer keds responses to common tick repellents, including DEET, picaridin, and IR3535. Unfortunately, keds did not react to any of the repellents, which do not appear to be an effective measure against keds. These results make some sense as keds find hosts through movement rather than chemical cues. However, 100% of deer keds died within 20 minutes of exposure to permethrin, so wearing permethrin-treating clothing should reduce the chance of being bitten by keds if they land on you. Two European studies found that keds are more attracted to dark-colored clothing than light-colored clothing, so wearing light colors during the fall when keds are active may also help reduce bites.

References and Additional Reading

Alekseev, E. A. 1985. Initial experience with individual human protection from attack by the deer louse fly Lipoptena cervi. Med. Parazitol. (Mosk) 6: 56–57.

Härkönen, S., Laine, M., Vornanen, M., and Reunala, T. 2009. Deer ked (Lipoptena cervi) dermatitis in humans – an increasing nuisance in Finland. Alces 45: 73–79.

Heine, K.B., Devries, P. J., and Penz, C. M. 2017. Parasitism and grooming behavior of a natural white-tailed deer population in Alabama. Ethology Ecology & Evolution, 29(3): 292–303. 

Kaitala, A., Kortet, R., Härkönen, S., Laaksonen, S., Härkönen, L., Kaunisto, S., and Ylönen, H. 2009. Deer ked, an ectoparasite of moose in Finland: a brief review of its biology and invasion. Alces, 45: 85–88.

Kaunisto, S., Ylönenm H., and Kortet, R. 2015. Passive sinking into the snow as possible survival strategy during the off-host stage in an insect ectoparasite. Folia Parasitologica 62: 038. 

Kortet, R., L. Härkönen, P. Hokkanen, S. Härkönen, A. Kaitala, S. Kaunisto, S. Laaksonen, J. Kekäläinen, and H. Ylönen. 2010. Experiments on the ectoparasitic deer ked that often attacks humans; preferences for body parts, colour and temperature. Bull. Entomol. Res. 100: 279–285.

Laukkanen, A., Ruoppi, P., and Mäkinen-Kiljunen, S. 2005. Deer ked–induced occupational allergic rhinoconjunctivitis. Annals of Allergy, Asthma & Immunology 94: 604–608.

Lloyd, J. E. 2002. Louse flies, keds, and related flies (Hippoboscoidea), pp. 349–362. In G. Mullen and L. Durden (eds.), Medical and veterinary entomology. Academic Press, San Diego, CA.

Maa, T. C. 1969a. A revised checklist and concise host index of Hippoboscidae (Diptera). Pac. Insects Monog. 20: 261–299.

Madslien, K., Ytrehus, B., Viljugrein, H., Solberg, E. J., Bråten, K. R., and Mysterud, A. 2012. Factors affecting deer ked (Lipoptena cervi) prevalence and infestation intensity in moose (Alces alces) in Norway. Parasites & Vectors, 5: 251; 1–10.

Olafson, P. U., Poh, K. C., Evans, J. R., Skvarla, M. J., and Machtinger, E. T. 2022. Limited detection of shared zoonotic pathogens in deer keds and blacklegged ticks co-parasitizing white-tailed deer in the eastern United States. Medical and Veterinary Entomology, 2022: 1–12.

Poh, K. C., Evans, J. R., Skvarla, M. J., Kent, C. M., Olafson, P. U., Hickling, G. J., Mullinax, J. M., and Machtinger, E. T. 2022. Patterns of deer ked (Diptera: Hippoboscidae) and tick (Ixodida: Ixodidae) infestation on white‑tailed deer (Odocoileus virginianus) in the eastern United States. Parasites & Vectors, 15: 31; 1–11. 

Poh, K. C., Skvarla, M., Evans, J. R., and Machtinger, E. T. 2020. Collecting deer keds (Diptera: Hippoboscidae: Lipoptena Nitzsch, 1818 and Neolipoptena Bequaert, 1942) and ticks (Acari: Ixodidae) from hunter-harvested deer and other cervids. Journal of Insect Science, 20(6): 19; 1–10. 

Samuel, W. M., Madslien, K., and Gonynor-McGuire, J. 2012. Review of deer ked (Lipoptena cervi) on moose in Scandinavia with implications for North America. Alces, 48: 27–33.

Skvarla, M. J. and Machtinger, E. T. 2019. Deer keds (Diptera: Hippoboscidae: Lipoptena and Neolipoptena) in the United States and Canada: New state and county records, pathogen records, and an illustrated key to species. Journal of Medical Entomology, 56: 744–760. 

Skvarla, M. J., Butler, R. A., Fryxell, R. T., Jones, C. D., Burrell, M. V. A., Poh, K. C., Evans, J., and Machtinger, E. 2020. First Canadian record and additional new state records for North American deer keds (Diptera: Hippoboscidae: Lipoptena cervi (Linnaeus) and L. mazamae Rondani). Journal of the Entomological Society of Ontario, 151: 33–40.

Vayssier-Taussat, M., Moutailler, S., Féménia, F., Raymond, P., Croce, O., La Scola, B., Fournier, P.-E., and Raoult, D. 2016. Identification of novel zoonotic activity of Bartonella spp., France. Emerging Infectious Diseases 22(3): 457–462.