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Hard-bodied Ticks: Family Ixodidae

Characteristics of genera

Family Ixodidae  Genus Amblyomma  Genus Hyalomma  Genus Ixodes  Genus Rhipicephalus 

Family Ixodidae (Hard-bodied Ticks)

Identification: A hard-bodied tick has a scutum (dorsal shield) which, in females, partly covers the upper body surface - or, in males, completely covers it. The gnathostoma (mouthparts or 'capitulum') includes the palps (feelers), chelicerae (jaws), and hypostome (a harpoon-like structure which helps anchor the tick in place). The gnathostoma of ixodid ticks is terminal and is visible dorsally. Eyes are sometimes present, located at the scutum margin. There is sometimes enamel (ornamentation) on the scutum and/or conscutum. There may be festoons (wrinkles) along the posterior margin and pulvilli (pads) at the ends of the legs. The legs of hard-bodied ticks may be striated, and are normally armed with internal and external spurs at base of coxa (the leg segment nearest the tick's body).

Ixodid ticks have three life stages - larva, nymph and adult - each of which requires just one very large blood meal before moulting. They remain feeding at the same site for several days secreting cement to attach to host. They may undergo either one-host or 2-host or 3-host life cycles depending on whether they target a different host for each life stage. Some ixodids are nidiculous or endophilic living in the nests or lairs of their hosts, but the majority of important species are exophilic - when hungry are found in the open, usually on the tips of vegetation from where they await passing hosts.

There are 14 genera of which the major ones are Amblyomma, Dermacentor, Hemaphysalis, Hyalomma, Ixodes and Rhipicephalus.

 

Genus Amblyomma (Bont ticks)

Identification: Unfed Amblyomma ticks are large at 6 to 7mm in length including mouthparts. The mouthparts are anterior and palp article 2 is longer than article 1 and 3. The basis capituli (basal part of the mouthparts) has straight lateral margins. The slender legs usually have pale rings and pulvilli are always present. A scutum (dorsal shield) is present in the female with a conscutum in the male. Enamel is present on the scutum and conscutum of many species. The colour of the enamel is predominantly pink to orange, or orange to red. Eyes are always present and may be flat or convex. Festoons (wrinkles in the posterior margin) are present in both sexes, but unclear in fed females. Spiracular plates are large and posterior to legs. Ventral plates in males are indistinct. The anal groove is posterior to the anus. Coxae 4 are of normal size and coxae 1 have unequal paired spurs.

 

Amblyomma americanum (Lone Star Tick)
Photos: Courtesy of Centres for Disease Control (James Gathany)

There are over 130 species of ticks in the genus Amblyomma. Most live in hot climates occupying a range of habitats. The early stages may feed on birds, rodents or reptiles, but adults mainly feed on larger mammals. The genus Amblyomma includes important disease vectors. Diseases transmitted to man or domestic animals include Rocky Mountain spotted fever caused by Rickettsia rickettsii, ehrlichiosis and anaplasmosis. We concentrate on three African species below. Amblyomma gemma which has recently been found to be a major reservoir of viral livestock diseases, Amblyomma hebraeum and Amblyomma variegatum which is a major pest worldwide.

Species: Amblyomma gemma   hebraeum   variegatum 

 

Genus Hyalomma (Bont-leg ticks)

Identification: Unfed Hyalomma ticks are large at 5 to 6mm including mouthparts. The integument texture has striations. The mouthparts are anterior and palp articles 2 are longer than articles 1 and 3. The basis capituli has medium angular lateral margins. Eyes are always very convex. The scutum/conscutum are coloured brown. Enamel is usually absent. The slender legs usually have pale rings and pulvilli are always present. Festoons are present in both sexes but are unclear in females when fed. Spiracular plates are large and posterior to legs Ventral plates are present in males only. The anal groove is posterior to the anus. Coxae 4 are of normal size and coxae 1 have large and equal paired spurs.

 

Dorsal view of male and female Hyalomma impeltatum
Photo: InfluentialPoints

There are about 30 species of Hyalomma which are found in Asia, Europe and Africa. Many have a 3-host life cycle but some have either a 1-host or 2-host life cycle. They may be the most abundant tick parasites of livestock in warm arid and semi-arid habitats. Several are of considerable veterinary or public health importance. The primarily Asian and North African Hyalomma anatolicum transmits the causative agents of a wide range of animal diseases as well as the human-infective Crimean-Congo haemorrhagic fever. Other important disease vectors are Hyalomma detritum and Hyalomma marginatum.

Species: Hyalomma rufipes  impeltatum 

 

Genus Ixodes (Ixodid ticks)

Identification: Unfed Ixodes ticks are medium in length (3 to 4mm) including mouthparts and the integument has striations. The mouthparts are anterior, and palp articles 2 are longer than articles 1 and 3. The basis capituli has straight lateral margins. Eyes are always absent. A scutum is present in the female and a conscutum in the male). There is no enamel (ornamentation) on the scutum or conscutum. Festoons are always absent. The slender legs never have pale rings and pulvilli are always present.

 

 

Ixodes ricinus (Sheep Tick)
Photos: InfluentialPoints

On the underside (see picture below) spiracular plates are large and posterior to legs 4. They are oval in males, but more or less circular in females. Ventral plates are present in males only. The anal groove forms a loop anterior to the anus. Coxae 4 are of normal size whilst coxae 1 have unequal paired spurs.

The ixodid genus includes important disease vectors of animals and humans and also some that inject toxins that can cause paralysis. Disease organisms transmitted to man include the bacterium Borrelia burgdorferi, that causes Lyme disease, and tick-borne encephalitis (TBE) virus. In addition the protozoan Babesia and the bacterium Anaplasma cause diseases in livestock.

Species: Ixodes hexagonus  ricinus 

 

Genus Rhipicephalus (Brown ticks)

Identification: Unfed Rhipicephalus are medium-sized ticks (3 to 5 mm including mouthparts). Their integument (cuticle / outer covering) texture has striations. Rhipicephalus mouthparts are anterior, the palpi are wider than long and the palp articles are all small. The basis capituli (basal part of the mouthparts, the 'gnathastome') has a hexagonal shape. Rhipicephalus legs are slender with pulvilli (pads) and usually do not have pale rings. A scutum ('dorsal shield') is present in the female with a conscutum in the male. Rhipicephalus are usually not ornate although four species have enamel. Eyes are present and rather flat (except in Rhipicephalus evertsi where they are bulging). Festoons (wrinkles) are present in both sexes, but unclear in fed females. Spiracular plates are large and posterior to legs. Ventral plates are present only in males, usually as two pairs. The anal groove is posterior to the anus. The fourth pair of coxae 4 are of normal size, whilst the first pair 1 have large and equal paired spurs.

Dorsal view of male and female Rhipicephalus evertsi
Photo: Courtesy of Armed Forces Pest Management Board under a Creative Commons Attribution License

There are about 74 known species in the genus Rhipicephalus. The dog tick (Rhipicephalus sanguineus) has a worldwide distribution, but otherwise species of the genus are restricted to the Old World especially Africa. They mainly occupy savanna and open woodland habitats and only feed on mammals. Most species are three host ticks. The genus Rhipicephalus includes important disease vectors. Disease organisms transmitted to domestic animals include Theileria parva, the causative agent of East Coast fever (ECF) in cattle, and Anaplasma spp. which cause bovine anaplasmosis.

Species: Rhipicephalus appendiculatus  praetextatus  pulchellus  sanguineus 

Acknowledgements

Whilst we try to ensure that identifications are correct, we do not warranty their accuracy. We have mostly made identifications using Walker (2001).  Further acknowledgements are given under each genus. These authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections.