Tsetse flies, Louse flies and Lice

Order Diptera (True flies)

Family Glossinidae (Tsetse flies)

Medium to large flies with wings held closed over abdomen; piercing proboscis projecting horizontally at rest sheathed by palpi; discal medial cell of the wing shaped like a cleaver and referred to as the hatchet cell; hairs on arista of antenna with further hairs branching off them. Tsetse flies are only found in sub-Saharan Africa.

Tsetse flies only feed on the blood of vertebrate animals. They are the main vectors of trypanosomes which cause human trypanosomiasis (sleeping sickness) and animal trypanosomiasis (nagana).

Glossina pallidipes (Tsetse fly)

Last two tarsal segments of the hind leg dark; all tarsal segments of front leg pale; fringe of long hairs on third antennal segment; bands on abdomen with rounded rather than squared-off corners; in female median scutellar bristles long; body length 8.5-11 mm. Widely distributed in East Africa especially in Kenya and Tanzania extending into Zimbabwe, Zambia and Sudan.

Biology & Disease Transmission: Female flies produce one larva at a time which is nourished within the uterus of the parent until it is fully grown; once a larva is mature, it is larviposited in a shady situation; the larva burrows into the ground, pupates and the adult fly emerges about a month later. Feed on wild antelopes, warthogs and buffalo and when available, cattle and man. An important vector of animal trypanosomiasis (mainly caused by the trypanosomes Trypanosoma congolense and T. vivax) and in some areas human trypanosomiasis (T. brucei rhodesiense).

This shows a Glossina pallidipes female taking a blood meal from the arm of the photographer. The photo was taken in a part of Kenya where there is only animal trypanosomiasis, so there was no danger of contracting the human disease. Human trypanosomiasis is surprisingly focal, only occurring in clearly defined areas, even though possible vectors may be much more widely distributed. Hence in Kenya you can only get sleeping sickness from being bitten by G. pallidipes in the Lambwe Valley area, even though G. pallidipes is found in many other parts of the country.

The first image shows a tsetse that has met its end while having its blood meal. Tsetse are 'pool' feeders which means they lacerate the skin with the mouthparts and then suck up the blood which flows into the lesion. Saliva is injected into the site which prevents clotting and may also contain infective trypanosomes. The second image shows a large number of tsetse caught in a trap.

Family Hippoboscidae (Louse flies or Keds)

Identification & Distribution: Dorsoventrally flattened; head sunk into an emargination of the thorax; palps neither leaf-like nor forwardly projecting, but forming a sheath to the proboscis. Antennae inserted into a depression and 1-segmented. Legs short and stout with strong and often toothed claws. Wings may be present or absent.

Biology & Disease Transmission: All species in this family are ectoparasitic feeding on the blood of mammals or birds. The degree of wing development varies between species with some being wingless, some winged and some loosing their wings after finding a host. They are often referred to as 'flying ticks'. Female flies produce one larva at a time which is nourished within the female's body until it is fully grown. After larviposition the larva pupates which in turn gives rise to the adult insect. Keds are not generally considered to be disease vectors - but see below...

Lipoptena cervi (Deer ked)

Wings fully developed and functional; tarsal claws simple, but with a pale basal lobe; humeral callus weak, not produced horn-like along side of head; wings clear and hyaline, with only one cross-vein; head much broader than long; thorax markedly flattened; body length 5-7 mm. Native to Europe and parts of Asia; introduced into the United States. Mainly feeds on deer but also where available on elk and other bovids. Once an adult fly has found a host, it looses its wings and remains on its chosen host.

This deer ked landed on us in Exmoor, UK where there is a large deer population. With the advent of global warming, the deer ked is now regarded as an invasive insect in northern Europe. Kaitala et al. (2009) document its spread into Finland in the 1960s feeding on moose. It is currently spreading further north, and there is experimental evidence that the species poses a possible threat to the reindeer herds ( Kynkäänniemi et al., 2010). Deer keds rarely bite humans and the bite is not very painful, but it can result in a long-lasting and recurrent reaction termed deer ked dermatitis ( Härkönen et al., 2009). This is thought by most to be an allergic reaction, but Dehio et al. (2004) has shown louse flies can transmit Bartonella, and Halos et al. (2004) suggest a role for this bacterium in the etiology of deer ked dermatitis.

Order Phthiraptera (Lice)

Family Pediculidae (Body lice)

Very small wingless insects living as ectoparasites on mammals. Eyes reduced or absent; antennae 3-5 segmented; mouthparts modified for piercing and sucking and retracted in head when not in use; tarsi 1-segmented ; claws single; setae normal and paratergal plates not projecting from body; abdominal cuticle unwrinkled and membranous except for genital region.

The Pediculidae are only found on primates, including man, but representatives of other families can be found on other mammal groups. Unlike ticks, lice normally remain permanently associated with their host.  

Pediculus humanus (Human Body Louse)

There are only three types of lice found on humans: the body louse (Pediculus humanus humanus), the head louse (Pediculus humanus capitis) and the pubic or crab louse (Pthirus pubis). The latter belongs to a different family (Pthiridae). The head of Pediculus humanus has distinctive dark eyes and the abdomen is elongate and lacks distinct tubercles; body length 2.3 - 3.6 mm. The body louse and head louse are morphologically indistinguishable, but the head louse is (on average) 20% smaller than the body louse. The body louse can transmit three diseases to man. Louse-borne (epidemic) typhus caused by Rickettsia prowazeki has traditionally been associated with wartime and insanitary condition, but worldwide still kills about 1400 people per year (WHO). Trench fever caused by Rochalimaea quintana is now mainly restricted to homeless people in Europe & America. Louse borne relapsing fever , caused by Borrelia recurrentis, mainly occurs during times of famine and war in Africa and around the Mediterranean.

This image shows an adult body louse - it is morphologically indistinguishable from the head louse. Body lice are only common where conditions are insanitary as a result of poverty or war. The head louse is much more common and has a worldwide distribution. It is certainly not restricted to insanitary conditions and high levels of infestation are reported from both 'developed' countries and from 'developing' countries (see for example Iwuala & Onyeka, 1977). In the USA the biggest problem appears to be denial of the infestation by parents, teachers and school administrators because they wrongly believe that infestations result from filthy conditions ( Weems & Fasulo, 2007). Fortunately, the head louse is not known to transmit any diseases.

Identifications & Acknowledgements Whilst we try to ensure that identifications are correct, we do not warranty their accuracy. We have mostly made identifications from our photos of living specimens. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. Most of the taxonomic information on families is summarized from Richards & Davies (1977) Pollock (1992) provides an easy-to-use key for the identification of tsetse flies.

References  Dehio, C. et al. (2004). Isolation of Bartonella schoenbuchensis from Lipoptena cervi, a blood-sucking arthropod causing Deer Ked Dermatitis Journal of Clinical Microbiology 42 (11), 5320-5323. Full Text  Halos, L. et al. (2004). Role of Hippoboscidae flies as potential vectors of Bartonella spp.infecting wild and domestic ruminants. Applied and Environmental Microbiology 70 (10), 6302-6305. Full Text  Härkönen, S. et al. (2009). Deer ked (Lipotena cervi dermatitis in humans - an increasing nuisance in Finland. Alces 45, 73-79. Full Text  Iwuala, M.O.E. & Onyeka, J.O.A. (1997). The incidence and distribution of head lice Pediculus humanus var capitis (Insecta Anoplura) in primary and post-primary school pupils in Nsukka, East Central State, Nigeria. Nigerian Medical Journal 7 (3), 274-283. Full Text  Kaitala, A. et al. (2009). Deer ked, an ectoparasite of moose in Finland: a brief review of its biology and invasion. Alces 45, 85-88. Full Text  Kynkäänniemi, S. et al. (2009). Threat of an invasive parasitic fly, the deer ked (Lipoptena cervi), to the reindeer (Rangifer tarandus tarandus): experimental infection and treatment. Annales Zoologici Fennici 47, 28-36. Full Text  Pollock, J.N. (1992). (Ed) Training Manual for Tsetse Control Personnel. Volume 1. Tsetse biology, systematics and distribution; techniques. FAO, Rome. Full text  Richards, O.W. & Davies, R.G. (1977). Imms' General Textbook of Entomology. 10th Edn. Chapman & Hall, London.  Weems, H.V. & Fasulo, T.R. (2007). Human lice: Body Louse, Pediculus humanus humanus Linnaeus and Head Louse, Pediculus humanus capitis De Geer (Insecta: Phthiraptera (=Anoplura): Pediculidae). University of Florida IFAS Extension Document # EENY-104. Full Text