Argasidae (Argas, Ornithodoros).
Collectively the Ixodidae and Argasidae may be distinguished from other Acari by the presence of a median probe, armed with recurved teeth, which project forwards beneath the mouth and between the palpi, and of a conspicuous spiracular area above and usually behind the base of the fourth leg on each side.
The two families Argasidae and Ixodidae may be distinguished as follows.
In the Argasidae the anterior portion of the dorsal surface of the body is extended forwards above the capitulum, so that this structure is concealed from above; the integument is fairly uniformly granular or coriaceous above and below; the palpi are simple and unmodified; there is no sucker beneath the claws in the adult, and there is only a slight structural difference between the sexes.
Both the Argasidae and Ixodidae contain pathogenic species, of which the best known are the following: Ornithodoros monbata, belonging to the Argasidae, and called bibo in Uganda, monbata in Angola, and tampan on the Zambezi, is widely distributed in tropical Africa from Uganda in the north to the Transvaal in the south.
It is singular that the Argasidae, which are for the most part parasitic upon birds, contain the only species of ticks, especially 0.